Etc

Front 1

Steps involved in the formation of the bilaminar embryo

Back 1

-zygote divides into the morula then the blastocyst
-cells of the inner cell mass rearrange into epiblast and hypoblast via differing adhesive properties
-the epiblast expands dorsally froming the amnion and amniotic cavity
-the hypoblast expands ventrally forming the primary yolk sac and releasing extraembryonic mesoderm cells

Front 2

Development of the oocyte from ovulation to fertilization

Back 2

-the prepature follicle in the ovary begins responding to FSH and LH
-oocyte matures and becomes polar
-oocyte is expelled into the peritoneal cavity.Ovum is surrounded by the zona pellucida, corona radiata, and associated cells
-ovum is collected by the fembriae and moved down the fallopian tube by smooth muscle contractions
-sperm moved up by swimming and smooth muscle contractions
-corpus luteum matures and secretes hormones

Front 3

Twinning (types)

Back 3

-fraternal: two (or more) eggs are released and fertilized
-monozygotic: cells splits when all are still totipotent
--early cleavage: 2 embryos, 2 placentas
--CM splitting: 2 embryos, 1 placenta (most common)
--ICM splitting with overlap: conjoined twins, may result in organ symmetry

Front 4

Ectopic pregnancy (definition and common locations)

Back 4

-When the embryo implants in non-uterine tissue. Constitutes an emergency because the fetus draws blood to it, risking hemorrhage on extraction.
- 54% ampullary, 25% isthmic (lower fallopian), 17% fimbrial, 4% interstitial, abdominal, ovarian or cervical

Front 5

Embryo development: fertilization to implantation

Back 5

- embryo divides as it travels down the fallopian tube
- day 4/5 blastocyst reaches the uterus and "hatches" from the zona pellucida
- day 6: trophoblast fuses with the endometrium on the ICM side. The synctiotrophoblasts surround the embryo and bury it in the endometrium and form the vascular network

Front 6

Events of Fertilization

Back 6

-spermatoza penetrate the corona radiata until reaching the zona pellucida
-sperm binds to zona pellucida via specific receptors on head
-sperm undergoes the acrosomal reaction releasing enzymes that bore a hole into the zona pellucida
-sperm membrane fuses with the ovum membrane releases DNA into the egg and triggering blocks to polyspermy

Front 7

Reactions/blocks that prevent against polyspermy in the egg

Back 7

-Fast: rapid depolarization of the egg membrane (-70 to +10). Prevents other sperm from adhering to the membrane
-Slow: calcium waves from the site of sperm entry induce cortical granules to fuse with the plasma membrane and release contents. This pushes the zona pellucida away from the zygote and hardens it

Front 8

Gastrulation (definition and steps involved)

Back 8

= movement of cells in the embryo to for the gastrula

- the primitive streak forms from the caudal end
-epiblast cells migrate to the primitive streak, pass through it and form the ventral endoderm layer, expanding caudally
-other epiblast cells make an epithelial to mesenchymal transition and from a mesodermal layer between the ecto and endoderms
-cells that pass through the primitive node (at the end of the primitive streak) become the notochord and precordal plate

Front 9

Define induction

Back 9

when antagonist cells signal to neighboring cells, triggering them to differentiate in a certain way

Front 10

TFG-β signaling pathway

Back 10

-TFG-β protein binds to a receptor in the plasma membrane
-receptor activates Smad protein, which complexes with a second Smad protein
-Smad complex moves into the nucleus and recruits other regulatory proteins
-complex activates transcription of specific genes

Front 11

Growth Factor signaling pathway

Back 11

- GF receptor phosphorylates itself upon binding GF
- Phosphorylated receptor activates Ras protein
-Ras protein activates MAP kinases
-MAP kinases phosphorylate and activate transcription factors which change gene expression

Front 12

Fundamental characteristics of signal pathways

Back 12

-Reception: receptor binds ligand
-Transmission: signal transduced through the cell, often through a G-protein coupled receptor
-amplification: signal is multiplied during transduction, allowing gene to be transcribed multiple times from one signal
-Outcome: often gene expression
-Termination: signal is stopped/degraded

Front 13

Define cell signaling

Back 13

when a cell releases a ligand that is received by another cell and usually induces change in the receiving cell by (de)activating transcription factors (signal transduction)

Front 14

Types of cell signaling

Back 14

-Inductive: cell triggers adjacent cells
-Gradient: response is based on ligand concentration
-Antagonistic: restricted gradient, response is based on the concentrations of ligand and antagonist recieved
-Cascade: cells successively signal adjacent cells
-Combinatorial: multiple ligands from multiple cells combine (Most realistic)

Front 15

Hedgehog signaling pathway

Back 15

-Hedgehog morphogens are processed within a cell and secreted.
-In the receptor cell, Patched recptors usually inhibit Smoothened receptors
-Hedgehog disrupts the binding of the two receptors so that Smoothened can send a
signal inside of the cell.
-Hedgehog functions based on a gradient of its concentration

Front 16

Wingless signaling pathway

Back 16

-Wingless functions on a gradient and is a morphogen.
-Its receptor protein is called Frizzled.
-Without a Wingless signal, the protein Disheveled is inactive, causeing Gsk3‐ß to phosphorylate ß‐catenin, so the latter degrades.
-With a Wingless signal, Disheveled is activated, so ß‐catenin cannot be phosphorylated and it goes into the nucleus to activate transcription.

Front 17

Notch signaling pathway

Back 17

-Notch signaling mediates lateral inhibition between adjacent cells
-A dominant cell differentiates then releases a signal to the cells around it, which trigger them to differentiate differently (ex: helper cells)
-The signaling protein Delta binds to the transmembrane protein Notch very tightly. The intracellular domain of notch is cleaved and travels into the nucleus to affect gene transcription.

Front 18

Transcription factors in gastrulation leading to polarity

Back 18

-in the bilaminar embryo the epiblast secretes Nodal and the hypoblast secretes an antagonist at the anterior end, setting up the anterior/posterior axis
-Noggin and Chordin from the notochord inhibit an inhibitor (BMP-4) allowing the neural plate to form
-cilia at the primitive node create a current so nodal is only expressed on the left side

Front 19

Levels of gene regulation

Back 19

Transcriptional
post-transcriptional modification
Translational
Post-translational modification

Front 20

Achondroplasia

Back 20

an inherited form of dwarfism resulting from defective signaling (growth factor FGFR3 is missing)

Front 21

Holoprosencephaly

Back 21

a disorder in which the embryonic forebrain fails to seperate fully, due to defective or absent Hedgehog signaling

Front 22

Hox Genes

Back 22

-encode homeodomain containing proteins
-involved in defining polarity
of the embryo
-Their arrangement on a strand of DNA correlates spatially to which body parts they affect during development.
-mutations can cause polydactyly and mis-arrangement of body parts

Front 23

Pax genes

Back 23

-homeobox containing genes
-control the expression of organs
-mutations will result in no development of organs or misplaced expression
-ex: Aniridia: no iris

Front 24

stratified squamous epithelia (description, function and locations)

Back 24

-multi-layered, surface cells are flattened and irregular
-protect against abrasion of moist tissues
-oral cavity, esophagus, vagina

Front 25

columnar epithelia (description, function and locations)

Back 25

-cells are taller than they are wide
-good for absorption (often have microvillae)
-intestine, gall bladder

Front 26

simple cuboidal epithelia (description, function and locations)

Back 26

-single layer of square cells, central nucleus
-excretory, secretory, or absorptive functions
-kindney tubules, salivary glands, pancreas

Front 27

simple squamous epithelia (description, function and locations)

Back 27

-single layer, flattened, irregular cells
-form a continuous lining, maintain selective diffusion barrier, good for moist surfaces
-endothelial lining of the circulatory system, mesothelial lining of the peritoneal cavity

Front 28

pseudostratified columnar epithelia (description, function and locations)

Back 28

-single layer though appearing multi-layered, elongated cells, nuclei in the basal 2/3 of the cell, often ciliated
-absorptive functions
-respiratory tract

Front 29

stratified cuboidal epithelia (description, function and locations)

Back 29

- 2-3 cell layers, square cells, central nuclei
- protection, secretion
- larger excretory ducts of the exocrine glands ex: sweat and salivary ducts

Front 30

stratified squamous keratinized epithelia (description, function and locations)

Back 30

- stratified squamous cells with a dead, denucleated layer on top (stratum cornea)
-resist abrasion, infection, desiccation
-epidermis

Front 31

transitional epithelia (description, function and locations)

Back 31

-Surface cells are dome shaped, large and pale stained, may be multinucleated; nuclei are large, round with prominent nucleoi; Luminal surface of the cells appears thick and more densely stained
-withstand stretch and toxicity
-urinary tract only

Front 32

Morphological characteristics of epithelia

Back 32

- number of cells: simple v. stratified
- shape of cells: squamous, cuboidal, columnar
-surface modifications:
--apical: cilia, microvilli, stereocilia
--lateral/basal: tight junctions, adherens junctions, desosomes, gap junction, hemidesosome
(- organization of cells: pseudostratified, karotinized, transitional)

Front 33

tight junction (zonula occludens)

Back 33

-barrier between the apical and basolateral membrane surfaces
-regulates solute movement in the paracellular pathway (in between cells)
-keeps membrane proteins in the appropriate domain (maintains cell polarity)

Front 34

Adherens junction (zonula adherens)

Back 34

-band below the tight junction
-attached to actin terminal web in adjacent cells, links the actin cytoskeletons
-uses cadherin molecules (Ca+ dependent) to span the intercellular space
-important for cell shape and motility

Front 35

Desosome (macula adherens)

Back 35

-spot adhesions between cells
-link the intermediate filament networks of adjacent cells (keratin) via cytoplasmic plaques
-highly organized, use cadherins to span the intercellular space
-important for cell integrity
-railroad track appearance on imaging

Front 36

Gap Junction

Back 36

-intercellular channels for small molecules ( <1000 MW)
-composed of connexin proteins, 6 group in a connexon which interacts with a connexon of an adjacent cell to form a channel. Connexons often form plaques.

Front 37

Hemidesosome

Back 37

-anchors intermediate filaments to the basement membrane
-prominent in epidermis

Front 38

Cilia

Back 38

-motile structures that move wave-like to propel fluid
-made of microtubules organized in "axoneme"
-common in the respiratory and female reproductive tracts

Front 39

microvillae

Back 39

-non-motile structures that increase surface area
-stabilized by actin filaments anchored in the terminal web
-found in the small intestine, and proximal kidney tube

Front 40

stereocilia

Back 40

-large, non-motile structures that facilitate absorption (are branched microvilli)
-supported by actin
-found in the epididymus

Front 41

Tissues formed from the ectoderm

Back 41

Neural tube: central nervous system (brain, spinal cord, retina, posterior pituitary), neural crest (peripheral nervous system)

Outer epithelia: anterior pituitary, lens + cornea, inner ear, epidermis and appendages, tooth enamel, anal and or epithelium

Front 42

Melanocytes: identity and origin

Back 42

-melanocytes are pigment cells in the epidermis
-derived from the neural crest, and migrate to the dermis then epidermis during development
-if mutated can result in albinism

Front 43

Langerhan cells: identity and origin

Back 43

- antigen presenting cells of the immune system
-mesodermally derived from precursors in bone marrow. During development they migrate to the epidermis

Front 44

Neuralation (steps)

Back 44

-the notochord induces the dorsal ectoderm to form the neural plate
- the neural plate folds laterally to form a groove and continues to fold up into itself.
-the two most lateral apical surfaces of the groove fuse and separate to form the neural crest.
-Closure of the tube begins midway and extends the closure so that there are only two open pores (anterior and posterior neuropores) at either end.
-Neural tube becomes CNS
-Neural crest cells undergo EMT and migrate away to form PNS

Front 45

Development of mammary tissue (as demonstrated by experiments with testicular feminization, TFM)

Back 45

the mesoderm, in the absence of testosterone, induces the ectoderm to develop an elaborate duct system in the breast tissue.

Front 46

Development of hair follicles

Back 46

Hair is generated by the downgrowth of epithelial cells induced by the mesodermal cells of the skin, the dermal papilla. The dermal papilla signal via FGF-5 to induce the epithelia to develop a hair follicle.

Front 47

Development of teeth

Back 47

-The dental papilla (mesencyhmal ectoderm from the neural crest) induces the oral epithelia to form down-growths into the papilla. These cells are converted to enamel. Dentin is formed from mesenchyme-dervide cells, filling in the cavity.

Front 48

Inductive interactions in skin differentiation

Back 48

-ectoderm induces mesoderm to differentiate into dermis
-mesoderm induces ectoderm to differentiate into epidermis
-the body location of the mesoderm determines the characteristics of the epidermis

Front 49

Characteristics and cause of ectodermal dysplasia

Back 49

- 2+ abnormal ectodermal features (generally in skin and skin appendages)
-due to mutations in ectodermal cell-cell communication, adhesion, transcription regulation, other functions
-EX: mutation in ectodysplasin pathway (signaling protein) results in anhidrosis (too little sweating)

Front 50

Epithelia derived from each germ layer

Back 50

Ectoderm: epidermis
Mesoderm: mesothelium, endothelium, epithelia of ducts and tubules
Endoderm: epithelia lining the gut and derivatives (respiratory tract)

Front 51

Tissues derived from the endoderm

Back 51

-gut (pancreas, liver, digestive tract, trachea, lungs)
-urinary bladder
-pharynx, thyroid, pharyngeal pouches

Front 52

Major derivatives of the neural crest cells

Back 52

-entire PNS (except axons of motor neurons)
-adrenal medulla
-melanocytes
-cranial neural crest cells contribute to the bones, dermis, fat, and muscles of the face and head

Front 53

Morphogenic movements of the endoderm that creates the gut tube

Back 53

- the endorm folds laterally while the entire embryo elongates and curves medially
- the outer endoderm and amnion fold around, creating tub of endoderm
- the yolk sac is constricted and reduced to a yolk stem

Front 54

tracheoesphageal fistula: characteristics and cause

Back 54

-during development the trachea buds off from the gut tube. A septum forms to divide it from the esophagus. If the septum does not form correctly a TEF results
-Most TEFs have an atetic or stenotic segment in the E or T
-4 types: TEF followed by a gap in the E, a gap in the E before the TEF, two TEFs with a gap in between in the E, TEF without gap

Front 55

How do derivatives of the gut form?

Back 55

The are induced to bud off from the main tube by signaling interaction with the surrounding mesenchyme cells

Front 56

What features distinguish eukaryotes from prokaryotes

Back 56

- membrane bound organelles
- cytoskeleton
- complex plasma membrane systems (important for communication with other cells) (and has cholesterol)

Front 57

The importance of compartmentalization in eukaryotic cells

Back 57

- localizes functioning and allows multiple different environments, optimized for different functions, to exist within the cell (increase efficiency)
- increase regulation (particularly though membranes)
- protection (isolate processes that could damage the rest of the cell)

Front 58

Importance of membrane fluidity

Back 58

- allows for proteins to diffuse and interact with each other
- important for signaling mechanism
-establishes cell polarity
-flexibility in adapting to the enviroment

Front 59

Membrane Fluidity and Asymmetry

Back 59

- different proteins and lipids are expressed in different areas of the membrane based on function creating cellular polarity
-fluidity is controlled by lipid tails (length and saturation), cholesterol

Front 60

Types of membrane proteins

Back 60

transmembrane: have domain that spans the membrane, usually made from alpha helixes with + charged amino acids on either end
membrane associated: anchored to the cytosolic surface by an amphipathic alpha helix.
lipid-linked: attached to either side of the bilayer by covalent attachment to a lipid molecule
Protein attached – attached by relatively weak, noncovalent interactions with other membrane proteins

Front 61

Lipid raft

Back 61

- patch of tightly packed lipids and cholesterols within the membrane creating a rigid segment
- have transmembrane proteins with longer transmembrane domains
-concentration of signal transduction receptors, acts as a “signaling platform.”

Front 62

Glycocalyx

Back 62

-a collection of sugars on the extracellular surface that are attached to glycolipids and glycoproteins of the plasma membrane.
-help protect the cell surface from mechanical and chemical damage, while aiding in cell communication and adhesion. -hydrophilic, conferring a negative charge and associated nucleophilicity to the cell.
-it's deterioration is a signal for cell death

Front 63

microfilaments

Back 63

The thinnest filaments of the cytoskeleton. They are polymers that allow cells to change shape by building itself up and breaking itself down (e.g. actin)

Front 64

intermediate filaments

Back 64

These filaments are static, providing mechanical support for stress (expansion or contraction). In the heart, intermediate filaments create a mechanical scaffold that allows the heart to beat without breaking down. They are often anchored to the plasma membrane at desmosomes and hemidesmosomes to provide connectivity. (E.g. keratins).

Front 65

microtubules

Back 65

These are long, hollow polymers that drive movement within a cell. Microtubules are the “railroad” on which vesicles are transported between organelles and the membrane. They have the ability to grow and shrink to give shape to the cell membrane. (E.g. tubulin).

Front 66

Nuclear envelope

Back 66

-double membrane contiguous with the ER
-segregates immature messengers and DNA from the rest of the cell
-nuclear pores: (8-point symmetry, basket and fibrils); selectively allows proteins and signals in/out of the nucleus

Front 67

Endoplasmic reticulum

Back 67

Rough ER: 1/3 of proteins synthesis, includes transmembrane proteins and secretory/excretory proteins
Smooth ER: modifies proteins, espeically hormones, produces cholesterols,

Front 68

Trans-location of membrane-bound proteins to the ER during translation

Back 68

-membrane bround proteins have signal sequence: 20AA hydrophobic sequence that binds to SRP and stops translation
-SRP complex binds to receptor on ER and nacent protein slides into a channel, translation continues
-signal protein is cleaved after transcription
-May also have stop-transfer sequences that make the protein transmembrane (rather than secreted protein)

Front 69

Glycosylphosphatidylinositol (GPI)-modification

Back 69

-After a protein has translated to the lumen of ER, cleavage of the C-terminus signal sequence creates a signal (set of AA) that allows the attachment of a complex lipid (GPI) anchoring the protein to the membrane
- GPI-bound proteins have the potential to end up in the extracellular leaflet of the plasma membrane, and these serve a purpose to concentrate proteins in the lipid raft and to direct proteins to different places in the cel

Front 70

N-linked oligosaccharide initiation

Back 70

-As the polypeptide chain is translocated into the ER lumen, it is glycosylated by oligosaccharide side chains at particular asparagines (ASN)
-Each oligosaccharide is transferred as an intact unit to the asparagine from a lipid called dolichol, catalyzed by a transferase
-Glycosylation plays an important role in helping the folding of proteins and also in the recognition of one cell by another on the cell surface

Front 71

Disulfide bonds in protein folding

Back 71

-Disulfide bonds are formed by an enzyme that resides in the ER lumen.
-Disulfide bonds help to stabilize the structure of the proteins that may encounter changes in pH and degradative enzymes outside the cell, either after they are secreted or after they are incorporated into the plasma membrane

Front 72

Golgi structure and function

Back 72

-cis face: faces ER, receives (and returns) proteins from ER via vesicles, other proteins will progress through the stack and be modified
-Trans face: facing plasma membrane, releases fully modified proteins for secretion/implantation
-medial: middle region
-Each region contains different set of modifying enzymes (biochemical asymmetry), especially for glycosylation
-Proteins sorting: proteins are tagged with signals that determine their ultimate destination (eg. lysosome)

Front 73

Endocytotic pathway

Back 73

-Molecules and receptors on the cell surface are engulfed by the plasma membrane, which invaginates and buds off.
-Binding of a ligand allows the receptor tail to bind GTP receptor proteins in the cytosol which recruit clatherin coat proteins and adapters. More coat molecules are recruited as invagination progresses
-Dynamin then forms a spring around the stalk and restricts it separating the vesicle
-A v-SNARE (transmembrane protein) and specific Rab proteins (GTP-ases) associate with the vesicle and are responsible for recognizing the target
-coat/cage is mostly released after budding is complete

Front 74

Receptor fates after endocytosis

Back 74

Recyling:
-acid in the endosome detatches the ligand from the receptor
-receptor (and sometimes carrier) bud off and return to the membrane
Degradation:
-receptor is moved to the lysosome and degraded
-shuts down the signal pathway
-acts a part of the signal transduction (endosome moves the receptor to different parts of the cell)

Front 75

Constitutive vs. Regulated endocytosis

Back 75

-Constitutive endocytosis occurs whether or not a ligand is bound to the receptor on the surface of the cell. The cell will continuously pull the receptor in and sort it. If no molecule is attached, the receptor is recycled and the process continues
-Regulated endocytosis is mediated by the binding of a ligand such as a growth factor to a cell surface receptor. The binding triggers internalization of the receptor, which initiates signal transduction

Front 76

Lyosomes

Back 76

- Responsible for degrading certain cell components and material internalized from
the extracellular environment
Key Features:
- single membrane,pH 5 (critical for enzyme function), acid hydrolases carry out
degradation reactions, can store heavy metals and calcium

Front 77

Vesicle targeting with SNARE and Rab

Back 77

- Snares on the membrane of the vesicles recognize snares in target organelles. They zipper together and bring the membranes in contact
-Membrane fusion is regulated by GTPases called Rabs -- multiple Ras create specificity. In order to bind, the vessicle Rab need to match the specific rab effector on the target membrane. Rabs/effectors bring the SNARES in contact and allow them to bind

Front 78

Peroxisomes

Back 78

small organelles that are responsible for breaking down materials brought into the cell. Peroxisomes contain enzymes that allow for oxidation of lipids and toxins. These are associated with Zellweger disease.

Front 79

Diseases of the endocyotic pathway

Back 79

There are many diseases associated with abnormalities in the endocytic pathway, in particular with abnormalities in the lysosomes. The main feature is that some enzyme in the lysosome fails to properly digest a key protein that leads to disease (Huntington’s, Parkinson’s, and Alzheimers)
-hypercholesterolemia: Disease can occur if endocytosis does not begin appropriately and the cell fails to engulf the appropriate molecules in the extracellular space

Front 80

Pathology of Familial Hypercholesterolemia

Back 80

-inherited disease (recessive or dominant depending) in which the cell is unable to recognize or use dietary LDL and so produces its own
-4 types:
Synthesis defect (receptor never made), transport defect (receptor degraded before reaching the golgi), defective receptor (can't bind LDL), clathrin defect (can't find clathrin to form coat and vesicle)
-Class 4: can have multiple types: nonsense, frame shift, false stop that determines the extent of the disease
-Statins work by turning off cell LDL production

Front 81

Intermediate filament structure and function

Back 81

Subunits are composed of an N­‐terminal globular, a C-­‐terminal globular tail, and a central elongated domain of an extended alpha-­‐helical region.The alpha-­‐helix allows for two subunits to wrap around each other forming a coiled-­‐coil dimer. Dimers associate to form a tetramer. The tetramer is the functional unit of IFs and come together to form long chains. Eight tetramer chains form a ropelike filament.
-There 4 different classes of subunits including keratins, vimetins, and lamins. (useful for determining tumor identity)
-IFs provide a scaffolding to withstand mechanical stress

Front 82

Intermediate filaments in epithelia

Back 82

- provide support and scaffolding in the cell against mechanical stress
- anchor cells to other cells and the basement membrane via desosomes and heidesosomes

Front 83

Intermediate filaments in neurons

Back 83

- stabilized and reinforce the axon and prevent against shearing forces

Front 84

Intermediate filaments in nuclei

Back 84

- provide structural for the nuclear envelope by forming the nuclear lamina
- also anchors cell membrane proteins and chromatin
- must be disassembled during mitosis

Front 85

intermediate filaments and tumor origin

Back 85

Because there are several types of IFs, antibodies to specific kinds can be used to identify the original tissue in metastatic tumors

Front 86

Functions of actin filaments

Back 86

- support microvilli (core has actin bundles, providing sturdy scaffolding)
- act as contractile bundles in the cytoplasm (esp. in muscle cells)
- form temporary structures such as dynamic protrusions, especially in cell migration
- form the contractile ring in cell division
- interact with adherens junctions to stabilize cell structure and interact with other cells

Front 87

Polarization of actin filaments

Back 87

Actin filaments have directionality:
- subunits are added more rapidly at the + end (though they can be added at the - end)
- addition/degradation at opposite ends allows for treadmilling of the filaments, and movement independent of myosin (listeria take advantage of this to move around)
- myosin motors can only move toward the + end

Front 88

Functional classes of actin binding proteins

Back 88

- nucleating proteins: bind and end of the filament to a membrane
- severing proteins: split a monomer into smaller subunits (usually during disassembly)
- cross linking proteins (in cell cortex): binds two crossing filaments into a mesh just under the PM
- capping proteins: blocks extension and degradation of the filament end
- side-binding proteins: binds to the side of the filament to regulate and stabilize contractility
- motor protein: forms contractile bundles (as in muscle)
- bundling protein (in filopodia): bundles proteins together in microvilli
- monomer-sequestering proteins: binds to subunits, preventing polymerization

Front 89

Function of myosin motor proteins

Back 89

- hydrolize ATP to move along actin/thin filaments.
- 30+ different types
- Myosin I: single contractile head, variable length tails, associates with membrane or vesicle to move things in around the cell
- myosin II: 2 contractile heads, exclusively in muscle cells
- myosin IV: important in hair cells and hearing

Front 90

Conformational changes in the myosin head that couple ATP hydrolysis to movement

Back 90

- Myosin is associated with a subunit on the actin filament
- Head binds ATP, releasing it from the filament
- Head hydrolizes ATP, causing conformational change that pivots it toward the + end and binds to a new subunit
- phosphate is released, causing the head to pivot back, pulling the filament (power stroke)
- ADP is released, allowing new ATP to bind

Front 91

kinesin

Back 91

- Motor protein family responsible for antograde movement in axons and contraction of the mitotic spindle
- Move toward the + end of mictotubules (though some can reverse). Can move continuously along the tubule.
- Motor proteins have two heads that interact with the microtubules

Front 92

dynein

Back 92

- motor proteins involved in movement of flagella & cilia (sliding movement along microtubules produces waving) and degradation of chromosomes
- move toward the - ends of microtubules
- Have a conserved large head domain

Front 93

Organization of microtubules in the cell

Back 93

- microtubules radiate outward from the microtubule organizing center (centrosome)
- The centrosome has two centrioles which are arranged perpendicularly to eachother, and may be used as templates for new MT synthesis
- MTs are nucleated at the centrosome at the - end
- in ciliated cell, centrioles duplicate, becomeing basal bodies, the organizing centers for cilia MTs (have 9+2 organization of MTs in cilia)
- during replication, centrosome is duplicated, and MT's expand from opposite poles of the cell

Front 94

Microtubule structure and assembly

Back 94

- MTs are made up of 13 parallel protofilaments. Each protofilament is made up of end to end heterodimers of α and β tubulin. α & β tubulin proteins each associate with GTP as a cofactor (important for assembly and dynamics of MTs). The β-tubulin subunit is toward the + end.
- can form doublet (flagella, cilia) or triplet (basal bodies, centrioles) MT's by splicing rings together
- MTs can self assemble in vitro, but in vivo it's very controlled: gamma tubulin forms a template at the minus end

Front 95

Microtubule polarity

Back 95

- + end grows more rapidly than the - end
- the - end is the nucleating end and is embedded in the centrosome
- MTs of the dendrite are of mixed polarity (unlike the axon)

Front 96

dynamic instability of microtubules

Back 96

- unless the end is capped or captured, MTs will always be continually growing and dis-assembling
- alternates between assembly at the + end and catastrophic disassembly via hydrolysis of the GTP associated β-tubulin
- this ends when the plus end is captured (and capped) and bound to stabilizing proteins

Front 97

Anti-microtubule agents as anti-tumor drugs

Back 97

Two mechanisms that upset the formation and function of the mitotic spindle, inhibiting mitosis and preferentially killing dividing cells
- cause MT depolymerization by destabilizing the MT structure or binding to and stabilizing free tubulin
- overly stabilize MT (ex taxol), causing a net increase in polymerization and preventing disassembly/shortening

Front 98

Functions of cilia

Back 98

3 classes:
- motile: move fluid and materials, protective barrier
- primary: immotile, involved in signal transduction
- sensory: involved in detecting sensory stimuli (sound, light)

Front 99

Mictrotubule organization in the mitotic spindle

Back 99

- MTs radiate from centrosome at opposite poles of the cell.
- 3 major MT types involved:
--astral: radiate in all directions, interact with dynein motors at the cortex, important in separating the poles in anaphase B (provide the force for separating chromosomes, anchor centromeres).
--kinetochore: attach to chromosomes and retract to separate them, undergo slow flux (treadmilling) despite being capped
--overlap: MT's form opposite poles overalap at the equator and push the poles apart with kinesin motors (anaphase B)

Front 100

Segregation of chromosomes during anaphase A by microtubules

Back 100

- once bound to the all the chromosomes, MT's retract to the poles by depolymerizing at both ends. Most shortening occurs at the kinetochore (+ end)
Two theories of movement:
- MT motor proteins at kinetochore use the ATP in the MT to move and consequently depolymerize the tubule
-kinetochore motor proteins have a higher affinity for polymerized subunits, so as the tubule depolymerizes they move toward the pole to maintain binding

Front 101

Activity of muscle types

Back 101

Skeletal: strong, quick, discontinuous, voluntary contraction
Cardiac: strong, quick, continuous, involuntary contraction
Smooth: weak, slow, involuntary contraction

Front 102

muscle fiber

Back 102

A muscle fiber is a single muscle cell. In skeletal muscle each fiber has several nuclei because it is formed by fusion of myoblasts
-The plasma membrane of the muscle fiber is the sarcolemma

Front 103

Paraxial mesoderm

Back 103

- develops adjacent to the neural tube
- develops into the somites, the dermis of the skin, axial and limb muscles, and axial skeleton

Front 104

Intermediate mesoderm

Back 104

- develops between the paraxial and lateral mesoderm
- gives rise to the genitourinary system (kidney, ureter, adrenal cortex, gonads, vagina, uterus, uterine tubes (not bladder or gametes)).

Front 105

Splanchnic (visceral) mesoderm

Back 105

- derived from the lateral mesoderm after it splits to form the coelom cavities
- gives rise to the mesenteries, the epicaridum, the blood cells/blood vessels, endothelium, the myocardium, the respiratory tract wall, and the gut wall (basically the tissues that’s intimately associated with the organs of the body).

Front 106

Somatic (parietal) mesoderm

Back 106

- derived from the lateral mesoderm after it splits to form the coelom cavities
- gives rise to the limb skeleton and the parietal tissue, or the tissue that covers the body wall.

Front 107

Lineage tracing to determine muscle origin

Back 107

- chick somites were replaced with quail somites, allowing researchers to see where those cells developed in the adult animal
- also can use fluorescent tracers, or engineering fluorescent proteins

Front 108

Development of skeletal muscle fiber from myoblasts

Back 108

- mononucleate myoblasts leave the cell cycle (fully differentiated) and fuse together
- assembly of the contractile apparatus pushes nuclei to the edge of the cell
- further growth of the fiber involves the fusion of satellite cells (muscle stem cells)

Front 109

Fast vs slow twitch muscle

Back 109

- slow twitch muscle have lots of mitochondria and blood supply (giving it a red color to due to the heme in the myoglobin)
- fast twitch has few mitochondria and less myoglobin because it relies on anaerobic glycolytic pathways to contract

Front 110

Coelom

Back 110

- cavity formed by the splitting of the later mesoderm into the splanchnic and somatic mesoderm. It forms the peritoneal, pleural, and pericardial cavities

Front 111

Splanchnic

Back 111

- of or relating to the viscera: visceral
- splanchnic mesoderm becomes most visceral tissue, or those that are intimately associated with the organs

Front 112

Viscus or visceral

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- an internal organ of the body, especially one located in the great cavity of the trunk proper (heart/liver).

Front 113

Somatic

Back 113

- of or relating to the wall of the body, parietal
- somatic mesoderm forms the parietal tissue, or the tissue that lines the body wall

Front 114

Parietal

Back 114

- of or relating to the walls of a part or cavity.
- The parietal tissue lines the body wall of an organism, as opposed to tissue that lines the organs themselves.

Front 115

Axial

Back 115

- relating to or situated in the central part of the body, in the head and trunk as distinguished from the limbs.

Front 116

Somite

Back 116

- one of the longitudinal series of segments into which the body of many animals is divided.
- somites are derived from the paraxial mesoderm, and organized into series of segmentally arranged blocks from the occipital region caudalward

Front 117

Mechanisms of bone formation

Back 117

- endochondrial ossification: cartilage model of the bone formed during embyrogenesis then calcified
- intramembranous ossification: direct ossification by mesenchymal cells (no cartilage intermediate)

Front 118

Developmental origins of the circulatory system

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- derived from the splanchnic mesoderm
- initially forms two parallel left and right systems. The parallel structures fuse and form the primordial heart in the 3rd week
-Initially the primordial heard is anterior to the oropharyngeal membrane but migrates as the embryo folds

Front 119

Major subdivision of somites and their adult derivatives

Back 119

- the ventromedial portion of each somite becomes the sclerotome which forms the axial bones.
- the dorsolateral and dorsomedial portions of the somite form the myotome and differentiate into muscle cells.
- The dorsolateral region forms the limb and body wall muscles while the more medial cells form the muscles of the back.
- The most dorsal part of the somite forms the dermatome that differentiates into the dermis.

Front 120

Signal pathway that differentiates axial bone in somites

Back 120

Sonic hedgehog (SHH), a secreted signal molecule expressed in the floor plate of the neural tube and the notochord, initiates PAX1 expression in presumptive sclerotome cells, and this transcription factor regulates differentiation of these cells into bone.

Front 121

Signal pathway that differentiates back muscle in somites

Back 121

Expression of the growth factor bone morphogenetic protein 4 (BMP4), by overlying ectoderm, causes secretion of WNT growth factors from the dorsal region of the neural tube. In turn, these growth factors cause expression of the muscle-specific gene MYF5 in the dorsomedial (closest) portion of the somite, and this gene regulates development of epimeric (back) muscle.

Front 122

Signal pathway that differentiates limb and body wall muscle in somites

Back 122

WNT proteins expressed by overlying ectoderm, together with BMP4 expressed by lateral plate mesoderm, turn on MYOD expression in the dorsolateral (closest to splanchnic mesoderm) part of the somite. MYOD is another muscle-specific gene that causes this region to differentiate into limb and body wall muscles (hypomeric musculature)

Front 123

Signal pathway that differentiates dermis in somites

Back 123

Dermis development is controlled by the transcription factor PAX3, the expression of which is initiated by the growth factor neurotrophin 3 (NT3), secreted by the (central) dorsal region of the neural tube.

Front 124

Mesenchymal-epithelial transitions and epithelial-mesenchmyal transitions in somites

Back 124

- The somitocoel cells that line the cavity are epithelial cells, having undergone an MET
- The ventromedial portion of the somite undergoes an EMT to become the sclerotome

Front 125

Hox 10 mutants in axial skeletal development

Back 125

- Hox 10 is normally expressed in the lumbar and sacral regions
- a mutation (deletion) in Hox10 genes allows for continued expression of earlier Hox genes, resulting in thoracic vertebral morphology (ribs) in lumbar and sacral regions and disrupts normal rostrocaudal differentiation.

Front 126

Function of cyclin dependent kinases in the cell cycle

Back 126

- control progress through the phases of the cell cycle with successive activation and deactivation (prevents regression)
- cdk concentration is stable, though activity oscillates throughout the cycle due to the presence of cyclins
- active cdk phosphorylates intracellular proteins that initiate, regulate, and terminate major events of the cell cycle.

Front 127

4 main classes of cyclins in cell replication

Back 127

- G1/S-cyclins – complex with Cdks (to form MPF) in late G1 and trigger progression through the restriction point and entry into S phase.
- S-cyclins – bind Cdks and help stimulate chromosome duplication; levels remain elevated until the beginning of mitosis.
- M-cyclins – activates Cdks which stimulate entry into the mitosis phase and cause cell division.
- G1-cyclin – binds to Cdks which then push the cell into the G1 stage after mitosis.

Front 128

G1 in cell cycle

Back 128

- This is a stage of growth directly after mitosis has created two new daughter cells.
- Provides time for the cell to monitor internal and external environment to ensure optimal conditions and preparation for proliferation.
- Cells may delay passage from G1 phase for even years if conditions are not correct.
- Includes a point of no return called the G1/S transition restriction point after which cells are committed to DNA replication and division.

Front 129

S phase in cell cycle

Back 129

- After G1, when chromosome duplication occurs.
- S-CDK responsible for initiating DNA replication once per cycle for cells:
Signaling cascade begins in G1 with the prereplication complex (pre-RC). S-CDK initiates nucleation of the pre-RC into preinitiation complex which unwinds the DNA helix and adds DNA polymerases/other replication enzymes. DNA is then replicated.

Front 130

G2 phase in cell cycle

Back 130

- phase after completion of DNA replication.
- Growth of cell and organelles to prepare for division of cell.
- Includes DNA damage checkpoint.
- Monitoring of internal and external environment to determine if ideal for cell division to commence.

Front 131

Mitosis

Back 131

- cell cycle phase in which division occurs
- 6 phases: Prophase, prometaphase, metaphase, anaphase, telophase, (and cytokinesis)

Front 132

cdk activation

Back 132

- cdk binds to specific cyclins as they become synthesized in the cell
- cyclin-cdk complex has 2 phosphorylation sites. Initially both are phosphorylated by activating and inhibitory kinases (primed complex)
- the inactivating phosphate is then removed by an activating phosphatase (active complex)
- the active cyclin-cdk complex inbibits the inhibitory kinase and activates the activating phosphatase, rapidly increasing overall cdk activity/signal
-

Front 133

cdk inactivation

Back 133

- cdk inactivation occurs when cyclin is degraded, which is mediated by ubiquitin (a protein tag for proteasome degradation; mechanism involves 3 protein complex that loads, transfers, and targets the signal)
- active cyclin-cdk activates a subunit which activates the E3 protein in the ubiquitin complex. Ubiquitin then rapidly labels cyclin-cdk for destruction in the proteasome, inactivating cdk

Front 134

Major events of the G2/M transition

Back 134

- cyclin, which has been slowly being synthesized during interphase, binds to cdk forming inactive MPF. which is then primed by phosphorylation by activating inhibitory kinases
- A small amount of MPF is activated by Cdc25 phosphatase, creating a positive feedback resulting in rapid activation of MPF and spike in MPF activity
- MPF activates numerous kinases (including nuclear lamins), triggering mitosis

Front 135

G1 restriction point

Back 135

- when the cell becomes independent of growth factor for triggering cell division
- The point at which the cell becomes committed to divide

Front 136

Growth factor mediated signalling for division during M1

Back 136

GF (mitogen) binds to PM receptor--activates Ras protein--activates MAP kinases--activates transcription factors--increases cyclin-D transcription--increased active G1 complex (cyclin-D/Cdk4)--activates G1/S complex (cyclin-E/Cdk2)---eventually accumulates enough that the cell no longer responds to this pathway and is committed to division (restriction point)

Front 137

Mechanism of G1/S transition past the restriction point

Back 137

- G1 and G1/S complexes, which have been triggered by GF signalling, enter a positive feedback loop of kinase activation.
- Both complexes phosphorylate Rb protein, inactivating it, releasing E2F (which then positively activates other E2F)
- E2F promotes transcription of S phase proteins further activating cyclin complexes (esp S cdk) and moving the cell toward synthesis

Front 138

S Cdk complex activation of synthesis

Back 138

- DNA replication is initiated in multiple places on the genome by origin recognition complexes (ORC) which are normally inactived by binding to Cdc6
S-phase Cdk phosphorylates Cdc6, releasing ORC and leading to Cdc6 degradation
- Unbound ORC is phosphorylated (active) and initiates replication

Front 139

Cell cycle checkpoints

Back 139

- end of S phase: ensure chromosomes fully replicated
- metaphase: ensure all chromosomes are lined up at the midline (this is accomplished by signals sent from unattatched kinetochores that suppress anaphase promoting complex (a cdk))
- end of S phase: repair any damage to DNA (damaged areas will recruit repair proteins while activating p53 which activates expression of p21, CKI, which inhibits S-phase cdk, preventing the cell from leaving S phase)
-

Front 140

G0 withdrawal

Back 140

- generally fully differentiated cells will no longer go through the cell cycle
- In G0, cells are kept from replicating by CKIs (cyclin-dependent kinase inhibitors) that bind cdk complexes.
- cells usually enter G0 if they are deprived of growth/divide signals during G1.

Front 141

Ataxia telangiectasia

Back 141

- A childhood neurodegenerative disease associated with an increased risk of cancers. This is caused by a defect in the ATM/ATR kinases, which are responsible for recruiting DNA repair enzymes and stalls the S-phase until the DNA has been repaired

Front 142

Xeroderma pigmentosum

Back 142

- A disease characterized by hypersensitivity to UV rays and an increased riskof melanoma. This is caused by a mutation in the DNA repair genes.

Front 143

Li Fraumeni syndrome

Back 143

- This is associated with an increased risk of a variety of cancers and is caused by a defect in p53, preventing the cell from activating p21 to stall S-phase entry and repair defective DNA.

Front 144

Retinoblastoma

Back 144

- A childhood tumor of the retina caused by unregulated cell proliferation because of defects in the Rb protein responsible for maintaining the inactivity of S-phase cyclins.

Front 145

Nuclear lamina

Back 145

- network of lamin filaments directly below the nuclear envelope (provides structural integrity)
- composed of 3 lamins. Lamin A/C are from the gene (different C-terminus splicing), B is a separate gene
- connects to the cytoskeleton, anchoring the nucleus in the cell via Sun/KASH complexes (overlap in the lumen of the nuclear envelope, Sun links to the lamina, KASH to cytoskeleton)

Front 146

Transport through the nuclear pore complex

Back 146

- to travel into the nucleus proteins are tagged with a nuclear localization signal which is recognized by a signal complex (α&β subunits) to form a cargo receptor complex. The receptor complex interacts with the NPC and passes through.
- Inside the nucleus Ran-GTP binds and releases the cargo from the complex which then exit via the NPC. Back in the cytosol the Ran-GTP is hydrolized to Ran-GDP, dissociating the carrier and α&β subunits

Front 147

Chromatin packaging

Back 147

- nucleosome: DNA is wrapped twice around histone octomers (H2A,2B,3,4) then associated with histone monomer (H1). Histone tails in these complexes are available for modification (important for chromatid structure)
- fibrils: nucleosome strand is coiled on itself into 30nm fibril
- Fibrils are then arranged in loops that are condensed into the chromosome
- Chromatin is most dense when packed in the mitotic chromosome
- Transcriptionally active "euchromatin" is less dense and central in the nucleus. Not active, "heterochromatin" is more dense and peripherally located

Front 148

Histone Code and DNA remodeling/regulation

Back 148

- Modifications to histone tails that are associated with certain chromatin states (i.e. availability for reading). Locally impact chromatin structure and recruit transcription factors
- possible modifications include acetylations, methylations, and phosphorylations
- histone modifying enzyme works in conjunction with chromatin-remodeling complex to make DNA available for transcription
- modifications to chomatin structure are collective known as the epigenome

Front 149

Chromatin as a target for chemotherapy

Back 149

- histone deacetylase (HDAC) inhibitors: block removal of acetylations from histone tails. Increase acetylation can disrupt gene expression, stopping cancer progression
- clinically seems to be effective in some leukemias

Front 150

Models of pathology in laminopathies

Back 150

- the lamina seems to be critical for nuclear/cellular integrity, particularly in cell undergoing mechanical stress (like muscle). Mutations therefore cause weaker adhesions (esp. in Sun/Kash complexes) and preferentially effect muscle due to high mechanical stress.
- Lamins and other nuclear envelop proteins interact directly with chromatin (and modying factors, TX factors). These interactions may influence gene expression, and mutation therefore could lead to altered expression and phenotype
- Emery dreyfus muscular dytrophy and other diseases result from mutated lamins

Front 151

Factors influencing animal and organ size

Back 151

- cell number (division vs death)
- cell size (synthesis vs. degradation of molecules/proteins)
- each of these factors is influenced by genetic patterns of expression and access to nutrients

Front 152

Neufield experiments on cell division vs. growth

Back 152

- alternately over expressed E2F (increased division) and Rb (reduced division) in embryos. Neither changed overall organism size relative to the control
- Showed that growth is not a consequence of division
BUT; division is sensitive to growth: starvation slows replication, growth must be "upstream" of division

Front 153

In vivo determinants of growth

Back 153

- intrinsic: pathways that act within a tissue to regulate its
growth down a preprogrammed developmental path
- Extrinsic: mediate the ability of a tissue to communicate
with other tissues and auto-regulate size
- Environmental: nutrient availability (sugars, amino acids) & use (e.g. muscle in bodybuilders)

Front 154

SRY gene is...

Back 154

the master regulatory gene in testes development

Front 155

Metcalf's experiments of local & systemic control of cell proliferation

Back 155

- Ist exp: transplanted multiple thymuses into a single host. Each grew to a full size demonstrating "intrinsic" growth control
- 2nd exp: transplanted multiple spleens into 1 host. Each grew to a fractional size proportional to the number in the body, demonstrating "extrinsic" growth control

Front 156

insulin-like growth factor (IGF-1) pathway

Back 156

- controls cell growth by increasing the biosynthetic capacity of the cell
- triggers production of ribosome subunit S6P and activates elF-4e which is a mRNA receptor and transcription factor
- Not found in yeast (no extrinsic signalling)
- Defects in ligand (IGF-1) or receptor (IRS-1) lead to fewer, smaller cells
- PTEN ("brake" in pathway) results in more, larger cells
- Dog size is a result of IGF activity

Front 157

TSC/TOR pathway (tuberous sclerosis complex/Target of rapamycin)

Back 157

- - controls cell growth by increasing the biosynthetic capacity of the cell
- triggers production of ribosome subunit S6P and activates elF-4e which is a mRNA receptor and transcription factor (same as IGF-1)
- TOR is nutritionally sensitive, activates in response to nutrient availibility

Front 158

Upstream open reading frames and growth dependent cell replication

Back 158

- cylin mRNA has 2 ORFs, one is upstream of the coding sequence and does not code for protein.
- Ribosomes will bind to the upstream ORF but fall off before the coding sequence.
- In high nutrient media, ribosomes are abundant due to TSC/TOR pathway, so more ribosome will reach the coding sequence and more cylin will be transcribed, moving the cell towards division.

Front 159

Myostatin as an extrinsic growth factor

Back 159

- TGF- β protein that inhibits muscle differentiation and growth. (External signal that stops muscle growth: extrinsic)
- Produced and secreted exclusively by skeletal muscle, circulated in blood
- Excess myostatin associated with muscle wasting, myostatin-mutants have 20-30% increase in muscle mass (Belgian Bull)

Front 160

Necrosis

Back 160

- passive, uncontrolled cell death that takes place in response to injury
- When undergoing necrosis, a cell will first swell, and then its membrane will disintegrate such that the cell contents are released into the local environment. This normally triggers a large inflammatory response

Front 161

Apoptosis

Back 161

- active, specific, highly regulated, molecular-mediated cell death
- requisite for normal development and tissue function
- in apoptosing cells, both the chromatin and nucleus will condense and fragment, and the cell will shrink. In the final stages, a process called “membrane blebbing” occurs in which portions of the cell protrude and bud off, forming apoptotic bodies. These bodies undergo phagocytosis by neighboring cells or by macrophages. Phagocytosis typically occurs quickly, to avoid an inflammatory response.
- development apoptosis helps to: sculpt tissues, delete structures, adjust cell numbers, eliminate harmful/injured/abnormal cells

Front 162

Biochemical signalling for apoptosis

Back 162

- Apoptotic stimuli (DNA damage, elevated p53, radiation, etc) activate BH3 (normally inhibited by Bcl-2) which promotes pore formation in mitochondria.
- Cytochome-C leaks out of mitochondria, bind with Apaf-1 and form the apoptosome.
- apoptosome cleaves the pro-segement in initiator caspases which activate effector caspases, which carry out apoptosis

Front 163

Extrinsic and intrinsic control of caspase activity

Back 163

- Extrinsic: pro-death ligands bind to death receptors which cleave and activate initiator caspases, which activate effector caspases
- Intrinstic: intrinsic death signals (radiation, DNA damage, mutations, etc) activate p53 pathway which activate BH3 to create pores in the mitochondria, allowing cytochrome-C to leak out, bind Apaf-1 and form the apoptosome which ativates caspases

Front 164

Oncogenes

Back 164

- when overactive these genes promote excess cell number or growth
- only one mutational event is required to gain dominant function an achieve cancerous phenotype
- Ex: Ras gene: if mutated to be permanently on, will increase growth and inhibit apoptosis

Front 165

Tumor suppressor genes

Back 165

- genes that would promote excess cell growth or number if inactivated
- Two mutational event needed to destroy tumor suppressor function (both gene copies), causing a recessive loss of function

Front 166

Caretaker genes in cancer

Back 166

- genes that maintain the integrity of the genome
- inactivation of these genes increases the chance of a cell to acquire mutations that are cancer promoting.
- two mutational events are required (knock-out both gene copies)

Front 167

Clonal evolution of human cancers

Back 167

= the idea that the compounded effects of multiple acquired mutations over time result in an aggressive cancer phenotype.
- Cancer is therefore a multi-step(mutation) process that "selects" for the most aggressively dividing cells
- Ex: stages of colon cancer

Front 168

66 acquired characteristics requisite for cancer development

Back 168

- self-sufficiency in growth signals
- insensitivity to anti-growth signals
- tissue invasion and metastasis
- limitless replicative potential (i.e. prevent telomere degradation)
- sustained angiogenesis
- evading apoptosis

Front 169

Viral origins of cancer (Rous chicken experiment)

Back 169

- Rous injected ground up tumor cell into healthy chicken, which then developed cancer. Therefore something in the tumor promotes tumorigenesis
- Rous sarcoma virus (RSV) found to carry mutated SRC oncogene that was incorporated into the host genome

Front 170

Mechanisms of oncogene hyperactivation

Back 170

- mutation: locked in a active or inactive state
- amplification: so much signal produced that it overwhelms regulatory mechanisms (Ex. Her2/neu receptor in breast cancer, activates Ras)
- translocation of the gene to an area of a strong enhancer/promoter (ex: Bcl-2 in Bcell lymphoma, inhibits apoptosis)
- translocation to create fusion protein with new function
- proviral insertion

Front 171

Discovery of tumor suppressors (Stanbridge experiment in 1976)

Back 171

- Clones of Hela tumor cells were implanted into mice.
- When normal human fibroblast cells (or hybrids with the Hela cells) were injected, no tumor observed--tumor suppressor active in normal tissue
- When chromosome 11 ejected from hybrids, tumor reformed--tumor suppressor on chromosome 11

Front 172

Knudon's "2-Hit" hypothesis for cancerous mutations in tumor suppressor genes, especially Rb

Back 172

- Loss of function mutations must occur in both gene copies (hence 2 hits) to get cancer
- In retinoblastoma predisposition for the disease is inherited, not the actual disease
--children with family history likely inherited 1 mutation, so achieved the second mutation earlier (and more likely in both eyes)
--in children w/o family history (sporadic), accumulated both mutations, so tumors later and mostly in 1 eye only

Front 173

Premises underlying the use of simple organism as models in medical research

Back 173

- most of the important biological processes have remained essentially unchanged throughout evolution (conserved in humans and simpler organisms)
- Conserved processes are easier to unravel in simple organism than in humans--humans are crappy model systems (expensive, old, complex)

Front 174

Hippo/Mst-2 Tumor suppressor pathway

Back 174

- highly conserved in flies and humans (associated with human cancer)
- When Hippo is deleted, tumors arise in flies.
-Crb (Crumbs) is an upstream regulator of the Hippo/Mst-2 pathway which also may be regulated by AIB-1 (amplified-in-breast-cancer-1)

Front 175

Translating cancer research in flies to treatments in humans

Back 175

- identify candidate targets for rational drug design
- facilitate development of targeted vs. general therapies
- genotype tumors to diagnose dependence of pathways and thus responsiveness to drugs
- tailor drugs to cancer genotypes

Front 176

Loose (areolar) connective tissue (organization, location, function)

Back 176

O: few cells, dispersed between disorganized fibers and abundant ground substance
L: beneath epithelia, between epithelium and muscle, serous membranes
F: holds blood supply, media for nutrient supply, supports epithelium, area for immune action

Front 177

Dense Irregular connective tissue (organization, location, function)

Back 177

O: bundled collagen fibers w/o specific orientation. Less cells and ground substance
L: capsules of organs (liver, spleen, lymph nodes, gonads), dermis
F: provide mechanical support and integrity

Front 178

Dense regular connective tissue
(organization, location, function)

Back 178

O: abundant collagen fibers, arranged in the direction of tension, cells are scarce w/ flattened nuclei
L: tendon, ligament, cornea
F: mechanical coordination and continuity between bone/muscle and bone/bone joints

Front 179

Fibroblast

Back 179

- "fiber forming cell"
- most abundant cell type in CT
- synthesizes ECM: collagen, elastin, proteoglycans, associative proteins
- organizes fibrils via membrane extensions surrounding them
- repairs damaged tissue (via metalloproteases)

Front 180

Reticular Cell

Back 180

- specialized fibroblast, produces reticular fibers of collagen III
- Reticular fibers form an elaborate network which interstitial fluid and wandering cells pass through.
- Reticular cells in lymph CT also participate in antigen presentation

Front 181

Unilocular adipose tissue

Back 181

- main adipose tissue in adults, often yellow
- has one central lipid droplet that occupies most of the cell. Nuclei are flattened and peripheral

Front 182

Multilocular adipose tissue

Back 182

- limited distribution in adults, common in newborns and hibernating animals, brown due to lots of mitochondria and blood
- multiple lipid droplets, central nucleus, lots of mitochondria
- used to produce heat by uncoupling ETC in mitochondria
-

Front 183

Ground substance/Proteoglycans

Back 183

- viscous, gel like substance in CT, water and ion reservoir
- fills the space between CT fibers, provides tissue resilience, lubrication/barrier, modulates fiber assembly and cell signaling

Front 184

Proteoglycan composition and function

Back 184

- Central protein core with several side chains of glycosaminoglycans, which vary in number and type
- The sugars forming the polymers can be modified. These modifications increase the negative charge of the side chains
-Negative charge of the side chains allow the complex to sequester water and ions and provides a repelling force that restores tissue shape when compressed

Front 185

Collagen Fibers

Back 185

- most abundant protein in the body
- confers tissue strength and rigidity
- many types, some form fibrils, others form meshes or associate and aid bundling of fibrils
- ex: CI in bone, tendon, skin, fibrous cartilage; CII in cartilage, CIII in loose CT, organs, blood vessels (elastin); CIV basement membrane
- multiple diseases associated with collagen

Front 186

Collagen structure

Back 186

- composed of 3 α helical subunits coiled around each other.
- in each sequence, Gly is every 3rd residue, which interact in the center of the helix complex, stabilizing it

Front 187

Collagen synthesis

Back 187

- synthesized as a monomer in the RER, modified by lysyl or hyroxylases (Vit C, Fe, O2 dependent) in ER lumen to form alpha helices
- interactions at the C-terminus ends drives assembly of the triple helix (disufide bonds) in the rest of molecule
- assembled subunits are secreted, C and N terminus domains are cleaved, remaining central rod spontaneously assembles into fibrils with others (stabilized by cross-linker, lysyl oxidase (Cu dependent))
- in fibers, subunits are staggered, leaving a lacunar region (impt for bone mineralization), creating banding

Front 188

Reticular fibers

Back 188

- made from collagen III, thin and branched
- stains with silver
- forms stable framework in organs

Front 189

Elastic fibers

Back 189

- confers elasticity and resilience to tissues, esp arteries, lungs, skin and ligaments/tendons
- elastin monomers are hyropobic and so resist expansion, will recoil
- lysyl residues are crosslinked by lysyl oxidase and condensed into desmosine crosslinks
- elastic fibers are polymerized on the fibrilin scaffold secreted by fibroblasts. Microfibrils surround elastin, and limit stretching

Front 190

Associative proteins in CT

Back 190

- glycoproteins which associate with CT fibers in the extracellular matrix and to cellular receptors (integrins)
- abundant in the basement membrane
- ex: fribronectin, laminin, tenascin, entactin

Front 191

Basement membrane/basal lamina

Back 191

- structural attachment site for overlaying epithelia and underlying connective tissue
- synthesized by epithelial cells
- rich in associative proteins binding to integrins
- Function: cell bonding & scaffolding, barrier & filtration, polarity cue fro epithelia, compartmentalization

Front 192

Integrins

Back 192

- transmembrane receptors. Extracellular domain anchors proteins to the cell's actin cyroskeleton.
- cells are mechanically connected to the ECM

Front 193

Function of Connective tissue

Back 193

- support and packing
- transport
- storage
- defense
- repair

Front 194

Pathophysiology for CT diseases

Back 194

• Haploinsuficiency: stop codon, null allele leads to loss of function, reduced secretion of wild type protein.
• Dominant Negative effects: mutations alter interaction with other protein, reduce stability or affect function.
- Enzymatic defects: compromises morphology and strength. Ex: mutations in enzymes involved in collagen synthesis, Brittle Bone syndrome
• Clinical consequences depend on function and location.

Front 195

Osteoblasts

Back 195

- bone forming cells, found on bone surface
- synthesize and secrete organic components of bone matrix and release factors aiding in mineralization
- become incorporated into bone as osteocytes
- when inactive, called bone lining cells

Front 196

Osteocytes

Back 196

- bone cells
- housed in cavities called lacuna with projections (canaliculi) to other cavities
- cell membrane extensions (processes) overlap in the canaliculi and transfer nutrients and signals via gap junctions

Front 197

Osteoclasts

Back 197

- bone reabsorbing/refoming cells
- multinucleated, migrate from blood vessels to bone, form a ruffled border to increase surface area.
- secrete HCl and proteases to decalcify and breakdown bone matrix
- creates Howship lacunae

Front 198

Bone matrix mineralization

Back 198

- composed of 70% mineral. Stores calcium as hydroxyapatite
- can occur directly, or by replacement of collagen precursors (endochondrial ossification)
- minerals released by osteoblasts (and chondrocytes, if in cartilage) as well as enzymes to disable inhibitors and recruit calcium
- minerals occupy the gap sites in collagen first then progress outwards