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172 Cards in this Set

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Why are membranes important?
Form walls, support organelles, compartmentalize cells for different functions, provide interface b/w cell and outside
What functions is membrane involved in?
Cell signaling, transport, growth, motility, adhesion b/w adjacent cells, and structural support
Describe plasma membrane.
Plasma membrane is composed of lipids, largely phospholipids (ex. phosphatidylcholine) in a bilayer structure. Phospholipids have hydrophobic tails and hydrophyllic heads (amphipathic). Lipids form bilayers in aqueous solution so hydrophobic tails inside and hydrophyllic heads outside and bilayer is inherently unstable and tends to curve.
What does it mean for the plasma membrane to be selectively permeable and what can cross it?
Only certain molecules can cross the plasma membrane. Highly lipid soluble molecules can enter easily. Very small polar molecules can cross too. Large polar or charged molecules (ions) cannot cross.
What provides lipid bilayer with fluidity / rigidity?
Double bonds create looser packing of lipids --> fluidity.
Cholesterol packed between phospholipids stiffens membrane.
The lipid bilayer is assymetrical with lipids synthesized inside cell and added to the inner layer, why does the inner membrane not grow disproportionately to the outer membrane?
Flipases selectively transfer phospholipids to outside membrane. This selectivity of flipases also makes membrane components on outside and inside membranes of cell different.
Smooth ER and Golgi create new vesicles of membrane and these are added asymmetrically so side inside Golgi contributes to outside of plasma membrane.
Where are glycolipids found and why?
Glycolipids found only on extracellular surface of membrane. Manufactured in Golgi and bud off --> vesicles fuse with plasma membrane and are inserted assymetrically so inside of golgi part is on outside of plasma membrane. Glycolipids have large carb. component on hydrophyllic end and are protective and involved in cell recognition functions.
Why are membrane proteins important?
Transporters, anchors inside and outside of cell, receptors, enzymes. Allow cell to move nutrients, communicate w/ outside environment, and change function according to signals from outside.
Name 2 ways in which proteins may be associated with lipid bilayer. Describe functionality.
1. Transmembrane - cross lipid bilayer, typically alpha helical whee they cross so hydrophyllic part like peptide bonds on inside of helix and hydrophobic side chains on outside. These proteins help create a pore or opening for hydrophyllic moleculues to enter and exit cell.
2. Membrane associated - does not cross entire bilayer, it attaches to inside or outside, may times linked to lipids or proteins that protrude from cell. Important for enzyme or anchoring functions, structural support or cell recognition.
What is the difference between glycoproteins and proteoglycans and what do these do?
On extracellular side of bilayer. Proteins bound to short sugars = glycoproteins and proteins bound to long polysaccharide chains = proteoglycans. Both of these provide protection nd cell recgnition
What is endocytosis and what are the two main types?
Endocytosis is the active uptake of materil into a cell by an invagination of the plasma membrane and its internalzation in a membrane bound vesicle. Two types are Pinocytosis and Phagocytosis.
What is pinocytosis?
Pinocytosis is "cell drinking." It is a constitutive process that allows for specific (receptor mediated) and non-specific uptake of fluid, macromolecules, and small particles. <150 nm.
What is phagocytosis?
Phagocytosis is the ingestion of large particles. Receptos mediated (like engulfment of "opsonized" bacteria") >250 nm
What is the process in which a cell targets its own organelles for degradation by fusion with the endosomal / lsosomal compartment?
Describe step-by-step the process of Pinocytosis of LDL during clathrin coated pit formation.
Receptors on cell membrane bind LDL --> Cargo selection (AP-2, adaptin) binds to receptors allowing selection and concentration of material --> Bud Formation occurs when clathrin binds --> Vesicles Form when Dynamin binds and pinches off coated pit -->Uncoating happens when vesicle is formed (adaptin and clathrin disassemble) -->early endosome (ph=6, no acid hydrolases) --> late endosome (ph = 5.5.,6, acid hydrolases H+ ATPase) j--> digested in lysosome pH=5
Explain the residual bodies and lipofuscin
Lysozymes filled with undigesed material are residual bodies and can be viewed as lipfuscin (wear and tar igment) under a microscope. This is cell trash.
What is the Gomori reaction used for and how does it work?
The Gomori reaction helps identify endosomal and lysosomal compartments. It is a metal precipitation reaction in which acid phosphotase from lysozome is used and lead phosphate is formed which is colorless and electron dense and then lead sulfate (black) can be formed by adding ammoniumsulfate
Describe the process of phagocytosis, setp-by-step.
(ex. done by macrophages or neutrophils) ingest larger materials, whole cells, debris. Coating (opsonins) --> Opsonization --> Recognition and Binding - opsonins recognized by receptors on surface on phagocyte and it binds --> Ingestion by Phagocyte, change in actin-myosin organization t engulf particle --> fusion with lysosome --> killed and digested phagolysosome.
What are te three filament systems that make up the cyoskeleton?
Actin (smallest, 6-8 nm), Intermediate filaments (8-11 nm), and microtubules (20-25 nm). Provide structure and functional organization to the cell.
Why is actin a dynamically assembled and disassembled filament?
G-actin or globular actin monomers polymerize in the same orientation lending polarity to F-actin. ATP binds to G-actin and stimulates polymerization while the ADP bound once F-actin is formed stimulates depolymaerization. This process creates dynamic assembly and allows movement of the membrane.
Why is actin polar?
G-actins usually ind in the same orientation lending polarity to F-actin. G-actins bind quicker to the positive end.
What actions does actin help perform in the cell / What are its functions?
Microvilli, contractile elements, filopodia and lamellipodia, contractile rings, give RBCs their biconcave shape, cellular motility and structural scaffolding.
What are integrins?
Assist in cell-sunstrate interactions. Anchoring proteins that help actin anchor to a substrate to allow movement along a substrate.
What do actin binding proteins do?
sequester g-actin so it is not all polymerized into f-actin, help in binding, even rows, cross-linking for membrane shape and structure
What are cytochalasins?
A drug that affects the actin cytoskeleton by preventing polymerization.
What does phalloidin do?
A drug that stabilized F-actin, it prevents depolymerization.
What are the two DYNAMIC polymeric filaments composing the cytoskelton?
actin and microtubules
What cell processes do microtubules play a significant role in?
Mitosis and transport (along mirotubule highway, ex. axons, centrioles, basal bodies, mititic spindle apparatus)
Explain mictrotubule polymerization and depolymerization.
GTP hydrolysis controls the growth of microtubule. Made up of alpha and beta tubulin heterodimers and assembled into polarized elements consisting of 13 protofilaments. Polymerization occurs at plus end and happens faster than the hydrolysis of GTP. Once GTP accummulates a cap forms to stop growth. When GDP is bound, depolymerization occurs. "dynamic instability"
What is the MTOC?
The Microtubule Organizing Center controls the number, orientation, and distribution of microtubules in the cell. Connected to the negative end of microtubules.
What are MAPs?
Mictotubule-associated proteins, they help organize microtubule arrays.
What does kinesin do?
It is a microtubule motor protein that helps move cargo from negative MTOC to positive end / cell periphery. anterograde
What does dynein do?
It is a microtubule motor protein that helps move cargo from the positive end to the negative MTOC end. retrograde.
Name two drugs that act on microtubules and explain how?
Taxol - stabilizes microtubules and colchicine inhibits microtubule polymerization.
What is an intermediate filaments primary role?
Structural! They are a more stable array of elements.
Do intermediate filaments exhibit polarity?
No their subunits assemble in an anti-parallel structure.
Describe the structure of an intermediate filament.
They are rope like, w/ 8 subunits per filament, they don't polymerize and depolymerize, they and an NH2 and COOH terminus and assemble in an antiparallel way.
Intermediate filaments have tissue specificity. Name 4 different intermediate filament types and where they are found.
Cytokeratins - epithelium
Vimentin - mesenchymal cells
Desmin - muscle
Neurofilaments - neurons
Glial fibrillary acidic proteins - glial cells
What is the function of a ribosome?
Provide cellular machinery for synthesizing proteins.
What is the structure of a ribosome?
Each ribosome is a complex of wo subunits, large and small. Each is made of rRNA.
What are the two places that most proteins are synthesized in the cell?
Free ribosomes and ribosomes associated with the RER.
Which proteins are synthesized on free ribosomes?
Proteins whose destination is intracellular including 1) soluble enzymes in cytosol 2) proteins for replacement or repair of organelles 3) nuclear enzymes 4) unique compnents of new plasma membranes
Which proteins are synthesized on RER?
1) all secretory proteins destined for exocytosis 2) lysosomal proteins 3) protein components of new plasma membrane
Explain how signal peptides work to target proteins to their appropriate destinations.
An SRP - signal recognition protein binds to signal sequence. SRP hen binds to the SRP receptor on the ER membrane and also to GTP. The translocon then opens to receive the polypeptide chain. The SRP and the receptor hydrolyze GTP and dissassociate from the translocon. Signal sequence is cleaved by signal peptidase. Polypeptide chaing enters ER lumen. Translation is completed and protein self-assembles.
The majority of proteins assume the correct 3-D conformation, what proteins may assist in this process. "protein synthesis quality assurance"
Chaperone proteins may assist. They correct proteins that are misfolded and tag incorrect ones for destruction by proteosomes.
Describe the structure and appearanc of the Rough ER.
RER is studded with ribosomes and engaged in protein synthesis. Lamellated appearance like stacks of pita.
Name 2 diseases associated with misfolded proteins.
Alzheimer's disease and Mad Cow disease.
Where does the glycosylation of proteins occur?
In the RER, N-linked glycosylation occurs, but ten modifid in Golgi --> glycosyation is a signal tag for proteins.
What is the function of the smooth ER?
Contains enzymes for a variety of metabolic processes. Has a tubovesicular morphology. Usually small but in some cells it is abundant. Important in 1) glycogen metabolism (liver and muscle) 2) detoxification using p450 complex (liver) 3) calcium storage (skeletal and cardiac muscle 4) lipid metabolism 5) steroid metabolism (ovaries, testis, adrenal glands)
What does the Golgi do?
Processes and sorts both secreted and membrane proteins. acts as "mailman" of cell.
1) Proteins go to golgi after ER where terminal glycosyation, phosphorylation, and sulfation of proteins occurs
2) proteoglycan synthesis
3) sorting of proteins to their destinations
Explain the transport of proteins from the ER to Golgi by COP-coated vesicles.
COPI and COPII shuttle proteins from ER to the Golgi. They are specific signal address peptides. COPI indicates to ER and COPII indicates from ER to Golgi. Proteins enter the cis-Golgi and exit the trans-Golgi.
What is the mannose-6-phosphate tag used for?
This tag is used for sorting of lysosomal enzymes in the Golgi and delivery of these proteins by clathrin coated vesicles to the late endosome / lysosome.
What occurs in the mitochondria and ow is the mitochondria structured?
Production of ATP. Aerobic energy supply, oxidative phosphorylation, Krebs Cycle. Mitochondria have 2 unit membranes that compartmentalize the organelle into 4 domains. The inner membrane has folds called cristae.
How is ATP made in the mitochondria?
Fatty acids and pyruvate creat acetyl-CoA which is then fed into the Kreb's cycle. This is then oxidized to give high energy electrons that are passed down the electron transport chain on inner mitochondrial membrane in order to make ATP using the ATP synthase complex. 1 mole glucose makes 36-38 moles ATP.
Why is your mitochondrial DNA all from your mother?
Cytoplasm all form mother and mitochondria in cytoplasm. Mitochondria have their own DNA.
This organelle is 0.2-1 micrometer and is involved in fatty acid oxidation, especially long chain fatty acids that mitochondria can't process. They also help in detoxification (ex. ethanol). Oxidasase and catalase are enzymes that work in this organelle to help it . They also help in the biosynthesis of plasmogens which is an abundant phospholipid found in myelin, which makes them important neurologically.
Peroxisomes. Especially found in liver, kidney and have about 50 enzymes.
These organelles are a pathway for endogenous protein degradation similar to lysosomes. All aged, misfolded proteins are ubiquitinated and targeted for degredation. They are then degraded in this organelle.
Proteasomes. "obsolete message shredder of cell" 20,000-30,000 proteasomes in average cell.
How are old proteins or misfolded proteins tagged for destruction?
By ubiquitin then degraded by proteasomes.
What is H and E dye and what does it allow you to see?
H is hematoxylin and it is a positively charged dye that is basophilic and allows you to see basic things like DNA or RNA. It is blue in color. E is Eosin and it is negatively charged and binds to acidic things and is acidophilic. It allows you to ee things like collagen, cytoplasm, hemoglobin and looks orange, pinky. Cells active in protein synthesis will show intense basophilia, dark staining where ribosomes are.
What is a-1 anti-trypsin deficiency disease?
It is an ER storage disease and causes emphysema. When things get in your lungs like dirt, pollution, bacteria --> macrophages phagocytose this stuff to keep lungs clean. When they do this they secrete elastase which if uncontrolled can eat away at lungs. Your liver normally produces a-1 anti-trypsin which breaks down elastase in your lungs. People with the disease have a mutation in the enzyme so it doesn't fold properly. The ER has quality assurance so misfolded proteins aren't released to the Golgi. The misfolded protein builds up in the ER and lungs continue to deteriorate and cisternae of ER are enlarged.
What is Zellweger syndrome?
It is a congenital disorder characterized by the rediction or absence of eroxisomes in liver, kidney, brain cells. So cells cannot beta oxidiz long fatty acids -->affects brain developmet and growth of myelin sheath. Symptoms are enlarged liver, mental retardation, jaundice, GI bleeding.
How big is the nucleus?
5-10 micrometers in diameter, but it's morphology can differ in different cells.
Give an example of an anucleated cell and a multinucleated cell.
Red blood cells are anucleate and skeletal muscles are multinucleated.
Explain the difference between euchromatin and heterochromatin and which one would you see in an active cell.
Euchromatin is transcriptionally accessible and dispersed, while heterochromatin is condensed, clumpy, and transcriptionally inactive. Euchromatin is present in an active cell.
What dye can be used to stain th nucleus, what would it look like in its active and inactive states with this dye?
Nucleus and the chromatin are basophillic so they can be stained with hematoxylin. In an active cell you will see a dark nucleolus and clear cytoplasm between the nucleolus and the nuclear membrane because there is dispersed euchromatin. If a cell is inactive you would see the clumpy, dark staining heterochromatin in the nucleus, so the cytoplasm would not be clear.
Describe the structure of the nucleus.
The nucleus has two unit membranes separated by the perinuclear cisterna. Outer membrane is continuous with the ER and can be studded with ribosomes. The nuclear membrane has pores for the transport of material in and out. The nucleolus is at the center of the nucleus and is the site of ribosome subunit assembly, rRNA synthesis. Fibrous lamina supports the structure of the nuclear envelope.
What are the two types of heterochromatin and how do they differ?
Facultative and Constitutive heterochromatin. Facultative is not transcribed often, DNA shut down until needed, it can be unwound and become euchromatin. Constitutive euchromatin is rarely transcribed, always condensed and usually found at the edge of the nuclear envelope (dark edge).
How are chomosomes packed to form a metaphase chromosome from the DNA double helix.
DNA is wound around an octameric histone core into nucleosomes to look like "beads on a string" formation of chromatin. Histones 2A,2B,3,4 are positively charged molecules that interact with the negatively charged DNA to form beads on a string or 10nm nucleosomes. The beads on a string then interact with Histone 1 to form 30 nm solenoids. The chromosome then condenses to form the metaphase chromosome.
The nuclear fibrous lamina is essential to supporting the nuclear envelope, what is it made up of?
Nuclear lamins A, B, C, a type of intermediate filament, and many proteins both intergral and peripheral. The fibrous lamina is a lattice network. The lamins help in the attachment of chromatin to the nuclear envelope, structural integrity of the envelope, and reassembly following nuclear envelop breakdown during mitosis.
How does the nuclear envelope breakdown during mitosis?
The breakdown is triggered, in part, by the phosphorylation of nuclear lamins.
What is the importance of nuclear pores? What are they composed of?
They are the transport channels in the nuclear envelope and allow things to flow in and out. 100 proteins make up the pores including nuclear porins. Small mols. diffuse freely and larger material is actively transported. Specific transport is mediated by import and export signals and chaperone molecules.
What is the NOR?
The nucleolar organizing regions of 10 chromosomes that contain ribosomal DNA genes.
What is NLS?
Nuclear Localization Signal --> importins act with pore fibrils and NLS to bring things into the nucleus.
What are the basic functions of the cell cycle?
1) To copy and pass on its genetic material to the next generation of cells, 2) To produce 2 genetically identical daughter cells, with accuratley replicated chromosomal DNA, 3) to correctly segregate the DNA into 2 cells, 4) duplicate organelles and macro-molecules
Which is the longest phase in the cell cycle?
Interphase - when cell transcribes genes, grows, differentiates, and carries out cellular functions. It has G1, S, and G2 phases. 25/30 hours
What occurs during the 3 phases of interphase: G1, G2, and S?
During G1 and G2 the cell grows and monitors internal and external conditions before commiting to M phase. During S phase or synthesis, DNA replicates.
What does the length of G1 depend upon?
The rate of cell division
When do cells enter G0? Give examples of cells that remain in this phase.
Cells opt out of the cell cycle during G1 and enter a quiescent phase, G0 if cell conditions are not ideal for division --> stay in G0 until conditions improve. Nerve cells and skeletal muscle cells permanently stay in G0 b/c they are terminally differentiated and don't divide.
What checkpoints must be passed at the G1 and G2 phases of the cell cycle?
G1 checkpoint - sufficient nutrients, DNA is intact and ready for replication.
G2 checkpoint - extracellular signals present, envrionment favorable, dNA replicated?
What is morphogenesis that occurs during embryonic development?
It is how organs acquire their unique shape through mutual signaling between cells during growth and reproductive phases.
Cell cycle control is dependent on cyclin dependent kinases. How are these activated and give an example.
CDKs are activated by cyclin (as in name) which allows them to be activated and phosphorylate proteins which then become active and intiate key steps in the cell cycle. Two kinases are mitotic CDK and S-phase CDK each controlled by M-cyclin and S-cyclin. Cyclin concentration vary in a cyclical fashion.
Explain the positive feedback mechanism associated with the cyclin cdk complexes.
M-cyclin activates mitotic cdk which then has a positive feedback and causes more M cdks to activate and buildup which then leads to mitosis, M phase.
Cyclins have to be destroyed cyclically, how is this done?
They are tagged by ubiquitin and fed to proteosomes at the end of their cycle.
Name 3 extracellular signal molecules required for normal cell division nd growth and their effect.
Mitogens - stimulate cell division
Growth factors- stimulate cell growth
Survival factors - promote survival, suppress apoptosis
What is p53?
It is a G1 checkpoint protein that monitors for damage in DNA and stops cell cycle. Mutation in this can lead to uncontrolled cell growth and cancer.
Describe the properties of the + and - ends of microtubules and describe the 3 microtubules that are present during mitosis.
- end is anchored to the centrosome and + end is dynamically unstable and can grow and shrink. When two mts from opposite sides overlap, motor proteins and other proteins cross-link them and stabilize them.
1. Polar mts - from pole to pole
2. Astral mts - from pole outwards
3. kinetochore mts from pole to kinetochore of chromosomes
When part of a chromosome is missing, this is called
When part of the chromosome is present in two copies, this is called
When chromosome breaks and a piece reverses and reattaches itself, it is called
When an error in cell division occurs and the chromosomes fail to separate, so both pass to the same daughter cell, this is
nondisjunction - results in monsomy, trisomy
Trisomy 21 = Down Syndrome
When the location of specific chromosome material attaches to another chromosome, this is
What are the three different positions of the kinetochore?
Metacentric - in the middle, submetacentric - slightly to one side, arocentric - almost all the way t one side
What is the difference between the centromere and the kinetochore?
Centromere - DNA where sister chromatids attach
Kinetochore - group of proteins on centromere where microtubules attach
What is the difference between necrosis and apoptosis.
Both are a means of cell death. During necrosis, the cell membrane disintegrates allowing lysosomal contents to enter the extracellular space and induce an infammatory response. During apoptosis, the nucleus undergoes fragmentation with loss of cell volume and cell membrane blebbing without loss of contents. Apoptoic bodies (like little vesicles) are phagocytosed. No inflamatory response.
Which form of cell death, necrosis or apoptosis, results in an infammatory response?
What family of proteases mediates much of the controlled cell involution occuring during apoptosis?
What is the function of cohesins?
They hold sister chromatids together (like rings)
What is the function of condensis?
They help make DNa wind up.
What preparation for mitosis occurs during interphase?
Replication of the DNA (S phase) and duplication of the centrosomes and centrioles.
Describe what a centrosome is and its structure.
Centrosome is MTOC of cell during mitosis. Composed of 2 centrioles (9 triplets of microtubules).
What happens durin Prophase?
1. Replicated chromosomes each w/ 2 sister chromatids condense (triggered by phosphorylation of condensin and H1) into mitotic chromosome
2. Initiation of mitotic spindle apparatus with polar, astral, and kinetochore mts and assoc. proteins (kinesin and dynein)
3. Rupture of nuclear envelope.
What happens during Prometaphase?
1. Nuclear envelope disappears and lamins phophorylated by M-CDK and disassemble
2. Chomosomes attache to spindle mts at kinetochores --> ready for active movement
What happens during Metaphase?
1. Chromosomes align at the equator (metaphase plate)
What Happens during Anaphase?
1. Anaphase promoting complex triggers the separation of sister chromatids by promoting the destruction of cohesins.
2. Sudden separation of chromatids
3. Poles pulled apart.
4. Initiation of cleavage furrow.
What happens during Telophase and Cytokinesis?
1. 2 sets of daughter chromosomes at poles of spindle
2. Nuclear envelope forms around chromosomes whe lamins are dephosphorylated they come together and put back pores and nuclear envelope
3. Cytokinesis goes from anaphase to telophase and a contractile ring of actin and myosin cleaves the cytoplasm
What would look like 6, 8, 13, and 9+2?
6 - 6 connexin proteins in a connexon for gap junction
8 - nuclear pore proteins
13- microtubules in a ring
9 + 2 - cilia
What is a tissue?
A collection of cells and their extracellular components that perform a common function. 4 types = epithelium, connective tissue, muscle, and nerve.
What are general characteristics of epithelial cells?
-tightly packed cells that are strongly connected
- very little extracellular space
-usually have a "free" surface (lumen or external environ.)
- supported by connective tissue
- avascular / no blood vessels (get nourishment from CT layer)
- polarized (cell surfaces structurally and functionally distinct)
-continuously renewed
What are the 3 major functions of epithelial tissue and what are some specialized functions.
1. Protection
2. Secretion
3. Absorption
special = sensory reception neuroepithelia), contractility (myoepithelia)
Epithelieal cells are polarized, what are their 3 distinct surfaces?
1. Apical (free) - faces exterior or lumen
2. Lateral - connected to adjacent cells via junctions
3. Basal - rests on basement membrane and underlying CT

Basal and lateral surfaces = basolateral domain
Describe the structure of microvili.
0.5-1 micrometers in length, fingerlike projectionsof cell membrane
contain a core of actin filaments linked by actin-bundlin proteins
actin flaments are anchored at base of microvilli to 'terminal web" = network of horizontal actin filaments w/ contractile properties
contraction of terminal web decreases apical surface and microvilli spread out
What is the function of microvili and name one place in the body they are found.
increase surface area of cell for absorption --> intestines and kidney
Describe the structure of cilia.
5-10 micrometers in length.
10 x larger than microvilli.
surrounded by cell membrane and have a central core (axoneme) of microtubules in 9+2 pattern (2 central and 9 outside pairs). cilia are anchored via attachment to basal bodies (modified centrioles below apical membrane).
What is the function of cilia and name one place in the body they are found.
motile projections that propel substances along the epithelial surface.
Respiratory tract - propel mucous
Uterine tubes - propel ovum toward uterus
What are sterocilia and where are they found?
Long microvilli found in male reproductive tract (epididymus- absorption) and ear (sensory reception). Not cilia and are not motile
What are the 3 types of projections found on the apical surface of epitheilial cells? Which one(s) is motile? List in order of size from smallest to largest.
Microvilli< Sterocilia< Cilia
Cilia are motile while microvilli and streocilli only move when cell contracts
What are 3 types of junctions found in epithelial cells?
1. Occluding junctions (tight junctions) - barriers to prevent flow of material
2. Adhering junctions (adhesion belt and desmosome) - bind cells for structural support
3. Communicating junctions (gap) - allow intercellular communication
How do you distinguish cilia and microvilli in TEM?
Cilia are crazy and long.
Mircovilli and organized in discrete ros (toothbrush bristles)
What do tight junctions do and where are they found?
Occluding junctions = tight junctions ad are found near apical surface. They seal off intervellular space from the ecteriori/lumen. Regulate movement through the paracellular pathway. Form complete band around each epithelial cell.
Describe the structure of a tight junction?
Formed by the binding of transmembrane proteinsfrom two opposing membranes or fusion sites. # of sites varies and this determines permeability.
What are the two types of adhering junctions?
1. Zonula adherens / adhesion belt cadherins
2. Desmosomes
Describe the structure and function of zonula adherens / cadherins type of adhering junctions in epithelia.
Provide structural support by linking cytoskeletons of adjacent cells. Have 3 components - transmembrane proteins, anchor proteins, and cytoskeleton. Transmembrane proteins are CAMS (cell adhesion molecules). In ZA these are cadherins. Cadherins are bound to anchoring proteins which are bound to actin in cytoskeleton. Form complete band around cell.
Describe the structure and function of desmosomes type of adhering junctions in epithelia.
Do not form complete ring.
Located below ZA.
MAde up of 2 disc-shaped attachment plaques (anchoring proteins) with transmembrane proteins between (cadherins). These anchoring proteins bind to intermediate filaments and are very strong --> can handle lots of stress.
Which type of adhering junction has anchoring proteins that bind to actin and which type to intermediate filaments? Which adhering junction is stronger?
ZA transmembrane proteins bind to actin while desmosome transmembrane proteins bind to intermediate filaments. Desmosomes are stronger.
Describe gap junctions in terms of their structure and function.
Communicating junctions consist of collection of transmembrane channels that allow small mols. like ions and hormones through. Formed by two connexons (each one with 6 connexin proteins). Connexins change conformation to open and close channel.
Can junctions be visualized?
No but junctional complex (ZO+ZA+desmosome) can be seen as terminal bar near apical surface.
What is the basement membrane?
Non-cellular layer that lies between basal surface of epithelial cells and underlying CT. composed of extracellular matrix proteins, primarily proteoglycans, type IV collagen fibronectin, laminin, and entactin. PAS staining!
What are the three layers of basement membrane?
lamina lucida, lamina densa, and lamina fibroreticularis
What does the basement membrane do?
Anchors and supports the epithelium.
Also is a barrier for the exchange of materials, regulates cell proliferation and provides surface for cell migration
What are the two types of junctions joining the epithelium and basement membrane?
1. Hemidesmosomes - only on basal surface, bind to intermediate filaments using integrins, only have 1 disc shaped plaque on epithelial side
2. Focal adhesions - anchor basal surfaces to basement membrane with integrins. Link to actin filaments.
What is the difference between hemidesmosomes and focal adhesions in the way they bind the epithelium to basement membrane?
Hemidesmosomes --> bind to intermediate filaments
Focal adhesions --> bind to actin
Epithelial cells are in two basic forms, what are they?
1. sheets (surface or covering epithelia) line cavities and free surfaces
2. glands - designed for secretion
not mutually exculsive
What are the three characteristics of surface epithelia?
1. number of cell layers (simple or stratified)
2. shape of cells of outer layer (squamous or cuboidal or columnar)
3. presences of specializations (cilia or keratin)
What are 2 special types of epithelia?
1. pseudostratified - appear stratified b/c some cells don't reach apical surface
2. transitional - stratified found in urinar tract and can stretch
What are two special types of simple squamous epithelium and where are they found?
1. endothelium - lines blood and lymphatic vessels
2. mesothelium - lines serous body cavities (like pleural cavity)
How are glandular epithelia characterized? (2 characteristics)
1. number of cells (unicellular or multicellular)
2. structure (exocrine - retain connection to surface or endocrine - release into blood)
What are 3 methods of secretions used by exocrine glands?
1. merocrine - exocytosis (typical like in goblet cells that are unicellular and secrete mucous into intestinal and respiratory tracts)
2. apocrine - secretory vesicles surrounded by PM (mammary and sweat glands)
3. holocrine - secreting cell destroyed (hair glands releasing oil)
Describe the two portions of multicellular exocrine glands.
Secretory portion and ducts.
How are multicellular exocrine glands named?
1 duct - simple gland
2+ ducts - compound gland
spherical shape of secretory component = tubular
grapelike shape of secretory component = acinar
or can be tubuloacinar
ex. is compound acinar
Endocrine glands release secretions into blood, their cells surround capillaries in 2 forms, what are they?
cords or follicles
What filaments are cilia made up of? What about microvilli?
Cilia - microtubules (9+2)
Microvilli - actin
Which type of epithelium is very very rare: simple squamous, stratified columnar, or stratified squamous?
Stratified columnar
What is a key characteristic of transitional epithelia?
Pillow or domes cells
In keratinined epithelia, can you see a nucleus?
No, you can only see the nucleus in unkeratinized epithelia.
The epididymus is characterized by what type of epitheilia and what is one of the features on the apical side of the cells?
pseudostratified columnar epithelia and stereocilia.
How do you recognize a plasma cell?
Clock faces, basophilic b/c of protein synthesis and a negatively stained golgi.
Do you need transmembrane proteins to transport water?
No, water can diffuse in and out of membrane.
What kind of connective tissue makes up the tendon?
Dense regular CT
There are two types of adhering junctions, the zonula adherens and the desmosomes, which one binds to actin and which one to intermediate filaments?
ZA- actin
desmosomes - intermediate filaments
Name what organelle the following are associated with:
cytochrome p450
acid phosphotase
p450 - smooth ER detoxification in liver
catalase - peroxisome (change H2O2 to water)
ubiquitin - proteasome
acid phosphotase - lysosome
Name the two components of connective tissue
Cells and Extracellular Matrix
What is the difference between procollage and tropocollagen?
Procollagen is the initial collagen secreted by the cell that is composed of 3 alpha strands. Once is secreted it is cleaved to mafe tropocollagen which then assembles outside the cell to form collagen fibrils.
What types of cells are in connective tissue?
Fixed (resident) and free (transient).
Fixed cells - fibroblasts and adipocytes
Free cells - mast cell, macrophage, plasma cell, leukocyte
ECM gives CT its specific properties. What are the components of the extracellular matrix of CT?
1. Fibers - collagen, elastic, etc
2. Structural Glycoproteins - laminin, fibronectin, etc.
3. Ground Substance - hydrated GAGs, proteoglycans
What does a fibroblast in CT do?
Makes the ECM, quintessential connective tissue cell, responsible for production and maintenance of ECM.
Where does a macrophage come from and what is its role in the CT?
Predominant transient cell. Derived from blood monocyte, is representative of mononuclear phagocyte system. Plays large role in tissue scavenging and immunological defense.
Macrophages are important for triggering the immune system as well.
What role does the mast cell play in CT?
Mast cells are from a bone marrow precursor, not blood. Do lots of secreting, see lots of granules in them. They are important in anaphylactic shock / allergies.
Transient cells that release:
1. heparin - anti-clotting
2. histamine - main thing it releases
and other substances in response to IgE triggered immune reactions.
What role do Mast cells play in anaphylaxis (hypersensitivity reaction) and what does histamine do?
Mast cells respond the 2nd time you are exposed to allergen --> release histamine and other pharmacologically active substances.
Histamine increases blood vessel permeability, increases smooth muscle contraction, increases mucus production.
What is used to counter anaphylaxis?
Epinephrine - vasoconstriction and increased BP
What do neutrophils do in the CT?
Phagocytosis of invading bacteria.
What do plasma cells in the CT do, how can you recognize them?
differentiated B cells that produce antibodies.
clock-face nuclei = hetero and euchromatin
-lots of RER - protein synthesis
and clear neg. stained Golgi
Collagen, the predominant fibrous element in the ECM is also the most abundant protein in the body. Describe its distinct amino acid composition.
Has glycine (every third), proline, and lysine. Proline and lysine residues are hydroxylated so that hydroxyproline and hydroxylysine can hydrogen bond in alpha helix chains.
Explain the role of Vitamin C in the formation of collagen.
Vitamin C - essential cofactor in 1.hydroxylation of proline and lysine residues --> necessary for Hydrogen bonding among alpha chains (scurvy caused by defficiency in vit C)
2. also important for lysyl oxidase which deaminates lysine and hydroxylysine so crosslinks formed (covalent bonds) among tropocollagen in fibril formation
Explain the biosynthesis of collagen.
Occurs through secretory protein pathway.
An alpha chain of proline, lysine, and glycine formed in cell. The prolines and lysines are hysdroxylated (using vit c) in the cell. Selected hydroxylysines are glycosylated. The three alpha chains self assemble into procollagen (triple helix). Procollagen is secreted in a vesicle, the proteins are cleaved and it is called a tropocollagen. Tropocollagens assemble into fibrils by covalent bonds (w/ help of lysyl oxidase). Fibrils form collagen fibers.
Name the 4 types of collagen and what tissues they make up.
Type I - bone, tendon, dermis
Type II - hyaline cartilage, intravertebral disk
Type III - reticular fibers (need silver stain to see), smooth muscle
Type IV - basement membrane
Elastic fibers are found in th ECM of some CT, describe their composition.
Like collagen but thinner.
No hydroxylysine.
Reveled by special elastic stains
Microfibrils made of glycoproteins contain fibrillin --> surrounded by amorphous elastin.
Desmosine and isodesmosine in elastin provide elastic properties. (Marfans syndrome = defect in fibrillin)
What role to desmosine and isodesmosine play in elastic fibers?
These are unique to elastin and are responsible for covalent bonds b/w elastin --> giving elastic fibers their elastic properties.
What is the role of structural glycoproteins in the ECM of CT and what are some examples - what do they do?
Structural GP - adhere connective tissues, cells, epithelia. Link elements of ECM to each other and cells within.
Laminin - helps in binding of basement membranes to epithelial cells
Fibronectin - Binds integrins to hold everything together
What is the function of the ground substance in ECM of CT?
Hydrated gel in which cells, fibers, and proteins are embedded. Essential for diffusion of nutrients, binds water, electrolytes, hormones.
What is the composition of the ECM of CT?
Viscous gel of glycosainoglycans (GAGs) long disaccharide repeats that are bound to a protein core. Proteoglycans are the GAGs bound to the protein core. --> create pockets for water.
Hyaluronic acid is one GAG found in synovial fluid, cartilage, umbilical cord.
What are the two types of connective tissue? Describe their appearance.
Loose and regular.
Loose --> irregular
Dense --> regular and irregular
Loose has lots of cells, few fibers, lots of granule substance
Dense has fewer cells, more fibers
Adipose tissue is a specialized connective tissue. What are the two types?
White (unilocular) and brown (mutlilocular) fat. Uniclocular has one fat droplet and multilocular has many. Brown is found in animals and infants --> generates heat, lots of mitochondria and uncoupling enzymes.