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143 Cards in this Set

  • Front
  • Back
How do cells cling to eachother?
Through direct cell-cell interactions

Bound by extracellular materials that they secrete
What is adhesion?
The ability of cells to cling or stick to their surroundings
What is one of the controlling aspects of cellular architecture (shape, strength, and arrangement)?
The mechanisms of cell adhesion
What are two building strategies of multicellular structures?
1) The strength of the extracellular matrix

2) The strength of the cytoskeletal filaments and cell-cell adhesions
What type of tissue is an example of the building strategy that relies on the strength of the extracellular matrix?
Connective Tissue
What type of tissue is an example of the building strategy that relies on the strength of the cytoskeletal filaments and cell-cell adhesions?
Epithelial tissue
What are epithelia?
Sheets of closely bound cells, found in epithelial tissues
What is the extracellular matrix of epithelial tissue?
Basal Lamina
What is the extra cellular matrix Composed of?
A network of proteins and polysaccharides
How thick is the basal lamina?
40-120nm thick
What types of cells do the basal lamina Surround?
epithelial, fat, muscle, Schwann Cells
Does the basal lamina have more than just structural support?
yes
In Kidney glomerulus the basal lamina provides a filtering function
What are four functions of the basal lamina?
Structural Support

Filtering

Determines cell Polarity

Promotes cell survival
What is the composition of the basal lamina?
Laminin, Type IV Collagen, nidogen, perlecan
What are the two linkers in the basal lamina?
nidogen & perlecan
what is the predominant cell type in the extracellular matrix?
fibroblasts
What does the Extracellular matrix influence?
Cell survival

Cell division

Cell migration

Cell shape

Cell function
What are fibroblasts found in bone?
Osteoblasts
what are fibroblasts found in cartilage?
Chondroblasts
What is the main function of GAG's?
To resist compression and serve as a space filler
What does Hyaluronan do in the extracellular matrix?
Acts as a space filler and facilitates cell migration
What are three glycoproteins found in the extracellular matrix?
Collagens

Fibronectin

Elastin
What are physical attachments between cells or between cells and the extracellular matrix?
Junctions (or Adhesions)
What are three classes of cell junctions in animal tissues?
Anchoring Junctions

Occluding Junctions

Channel-Forming Junctions (Gap Junctions)
What type of junctions are both cell-cell and cell-extracellular matrix adhesions, linked with cytoskeleton and transmit stresses?
Anchoring Junctions
What types of junctions seal the gaps between cells in the epithelia, which also make the epithelial sheet impermeable to outside molecules?
Occluding Junctions
What types of junctions create passageways that link the cytoplasm of adjacent cells and allow passage of small molecules and ions from cell to cell?
Channel-forming junctions or Gap Junctions
What are the two types of anchoring junctions?
Those linked to the actin cytoskeleton

Those linked to intermediate filaments
What are desmosomes?
Cell to cell adhering junctions associated with intermediate filaments
What are hemidesmosomes?
Cell to Matrix junctions associated with intermediate filaments
What are adherin junctions?
Cell to cell junctions associated with the actin cytoskeleton
What links the cytoskeleton to extracellular structures in anchoring junctions?
Transmembrane adhesion proteins
What are the proteins that mediate attachment of cell to cell?
Cadherin
What are the proteins that mediate attachment of cells to the matrix?
Integrin
What do cadherins depend on?
Calcium Ions
What happens to cadherins when Ca is removed from the extracellular medium?
They come adrift
What is the process whereby cells are joined by cell-cell junctions so that the outer surface of the embryo becomes smoother?
Compaction
What type of binding occurs between cadherins?
Homophillic
What is homophillic binding between cadherins?
Specific cadherin molecules of one subtype bind to cadherin molecules of the same subtype on adjacent cells
How do cells of different types not bind with cadherin proteins?
Cadherins mediate highly selective recognition
Where does the interaction between two cadherin molecules occur?
At the N-terminal tips
How does calcium regulate the cadherin function?
Calcium allows the protein to remain rigid. Without calcium ions, the protein would become floppy.

The lack of calcium binding also destabilizes the protein
What do attached cadherin proteins function like?
Velcro

They are strongly joined but also easily peeled apart
What does the linkage of cadherin to the cytoskeleton depend on?
Accessory Anchor Proteins
What connects actin bundles via cadherins from cell to cell across the epithelium?
The Adhesion Belt
What can help an actin network of the adhesion belt to contract?
Myosin Motor Proteins
What does the desmosome connect cell-cell?
Intermediate filaments
What is the main function of desmosomes?
To provide mechanical strength
What do the cadherins of the desmosome bind to in the cell?
A dense plaque of intracellular anchor proteins
What proteins are used for linkage in the hemidesmosome?
Integrin Proteins
What is another term for occluding junctions?
Tight Junctions
What are two functions of occluding junctions (tight junctions)
To seal the gaps between the cells

Act as fences to separate domains within the plasma membrane of each cell which maintains polarity of individual cells.
What junctions play a role in the transport of glucose in epithelial cells?
Tight Junctions
How do tight junctions help regulate the transfer of glucose in epithelial cells?
They confine glucose transport proteins to their appropriate membrane domains
What are the proteins that form the tight junction?
Claudins and Occludins
What protein complexes are associated with gap junctions?
Connexons
What are connexins?
Four-pass transmembrane proteins, a group of six forms a hemichannel or connexon.
What are two functions of gap junctions?
Allows action potentials to spread rapidly from cell to cell

Allows neighboring cells to share signaling information and act in a coordinated way.
How are gap-junction channels similar to ion channels?
They do not remain continuously open, but flip between open and closed states by extracellular signals
How thick are actin microfilaments?
7nm in diameter
What is the basic subunity of actin microfilaments?
Globular actin (G-Actin)
Where can actin filaments generally be found?
Microvilli

Stress Fibers

Lamellipodia, Filopodia

Contractile Ring
How are actin filaments polymerized?
Actin with bound ATP joins to the strand at one end
How is actin filament's behavior modified?
Through Actin Binding Proteins
What proteins influence nucleation of the actin filament?
Actin-Related Proteins (Arp complex)
On what end is the actin filament nucleated by the Arp complex?
The negative end
What protein influences bundling of actin filaments?
Myosin II
What are the proteins that influence non-contractile bundling and sheets?
Arp 2/3 Complex (lamellipodia)

Villin (microvilli)
What protein influences actin molecular motors?
Myosin I
What are the functions of Myosin I?
Membrane Trafficking

Cell Motility

Cytokinesis

Organelle Transport
Where is Myosin II generally located?
Skeletal Muscle

Smooth Muscle

Nonmuscle
What is tensegrity?
Tensional integrity by a self-stabilizing architectural system.
What is a structure with the highest ratio of enclosed area to external surface area and in which all structural members are equal contributors to the whole?
Geodesic Dome
How do the viscoelastic materials help a cell?
It absorbs stress energy in the bonds of polymeric molecules and deformation occurs according to the viscosity. Removal of stress produces a slow return to original shape.
What are the results of a mechanical force on a viscoelastic substance?
An initial resistance

Slow deformation

Slow return to original form after removal of force
Start @ L-21
Page 7
What are the three subphases of interphase?
G1

S

G2
What is an essential prerequisite for cell division?
DNA replication
What occurs during G1?
Cell Growth

Gene Transcription

Protein Synthesis

DNA Repair

Monitors/Responds to External Stimuli

Organelles Divide
What phase is the extended resting state?
G0 Phase
What cells remain permanently in G0 state?
Nerve Cells, Skeletal Muscle Cells, etc
What occurs during the S Phase?
DNA replication

Centrosome Replication
What occurs during the G2 phase?
Cell Growth Similar to G1

Preparations for M Phase (Checkpoints)
What are the five subphases of M phase?
Prophase

Prometaphase

Metaphase

Anaphase

Telophase
What is the term for the cytoplasm dividing in two?
Cytokinesis
What occurs in prophase?
Replicated chromosomes condense

Sister Chromatids are joined together by cohesin

Mitotic Spindle starts to assemble

Centrosomes separate

Kinetochores form on Centromere Region
What protein aids the condensing of DNA in prophase?
Condensin
How does condensin aid in condensing DNA chromatids?
Condensin forms ring like structures to help coil the mitotic chromatids into smaller more compact structures
What holds the sister chromatids together?
Cohesin
When do cohesins assemble on the sister chromatid?
In the S Phase
What stabilizes the microtubules?
The interaction of the microtubules from one centrosome to the microtubules of the other centrosome
What are the two centrosomes called after forming the mitotic spindle?
Spindle Poles
What do the kinetochores attach the chromosomes to?
The Mitotic Spindle
When do kinetochore microtubules attach to the kinetochore?
Prometaphase
What occurs at prometaphase?
Breakdown of the nuclear envelope

Attachment of spindle microtubules through their kinetochores
What aids in the disassembly of lamina for the breakdown of the nuclear envelope?
The phosphorylation by mitosis promoting factor
What occurs during Metaphase?
Kinetochore microtubules attach to opposite poles of the spindle.

Chromosomes align at the equator of the spindle, the metaphase plate
What are the three populations of spindle microtubules?
Kinetochore, Interpolar, and Astral
What do the interpolar microtubules attach to?
Other interpolar microtubules of the other centrosome
What do the Astral microtubules attach to?
Nothing
What occurs during anaphase?
Sister chromatids separate toward the spindle poles
What triggers the separation of sister chromatids by promoting the destruction of cohesins?
Anaphase Promoting Complex (APC)
How does APC promote the destruction of cohesin?
It catalyzes the destruction of securin, which inhibits separase. With the destruction of securin, separase is free to cleave the cohesin complexes.
What are the two types of movement during Anaphase?
Anaphase A

Anaphase B
What type of movement is characteristic of the movement of chromosomes toward poles by depolymerization of kinetochore microtubules and action of motors?
Anaphase A
What does Anaphase B move?
Moves the poles apart by the elongation of interpolar microtubules and the action of motors on interpolar and astral microtubules
What occurs during telophase?
Kinetochore microtubules depolymerize

Interpolar microtubules elongate further and continue to push

Nuclear envelope reforms

Condensed chromatin expands

Contractile ring forms, identifying the plane of division
How is does the nuclear envelope reform during telophase?
The nuclear pore proteins and nuclear lamins are dephosphorylated
What occurs during Cytokinesis?
Cytoplasm is divided in two by contractile ring

Tightening of ring produces cleavage furrow.

Reformation of interphase cytoplasmic microtubules

M phase ends --> Cell Enters G1 Phase
What triggers the major processes of the cell cycle?
The Cell Cycle Control System
What determines whether or not the cell proceeds to the next phase of the cycle?
Checkpoints
What does the G1 checkpoint check for before entering the S Phase?
A favorable environment
What does the G2 checkpoint check for before entering Mitosis?
DNA is replicated

All DNA damage repaired
What does the Mitosis checkpoint check for before pulling the duplicated chromosomes apart?
The chromosomes are properly attached to the mitotic spindle
What are the two key families of proteins that control the cell cycle?
Cyclins

Cyclin-Dependent Protein Kinases (CDKs)
What are cyclins?
Regulatory subunits of the cyclin-dependent protein kinases
What are cyclin-dependent protein kinases?
Kinases involved in the initiating and sustaining events of the cell cycle
What activates a Cdk?
Cyclin
Is cyclin or Cdk variable in the cell?
Cyclin levels rise and fall with the states of the cell cycle
When is Cdk activity low?
Interphase
What are the four major types of cyclin-cdk complexes?
G1
G1/S
S
M
What must occur for a Cdk complex to be active?
It must first be phosphorylated by protein kinases, then two of those inhibitory phosphates must be removed by the activating protein phosphatase.
What is the G1-Cdk activation induced by?
Growth Factors, Hormones, Oncogenes (Ras)
What does the G1-Cdk complex help with?
Helps to drive the cell through G1 toward S
What does the G1/S-Cdk trigger?
Triggers entry into S phase
What does S-Cdk activate?
The origins of replication leading to DNA replication
How does S-Cdk begin the replication process and only allow it to be replicated once?
It causes pre-replicative complex to bind to the origin of replication

S-Cdk triggers the degredation of phosphorylated Cdc6
What does damaged DNA activate?
p53 protein
What does p53 protein bound to DNA stimulate?
Transcription of Cdk inhibitor protein p21
How can DNA damage arrest the cell in the cell cycle?
By the creation of the p21 inhibitor protein that binds to G1/S-Cdk and S-Cdk to inactivate them.
What is cell death?
Apoptosis
What phosphorylates the M-cyclin-Cdk complex at one site?
Cdk-Activating kinase
What phosphorylates M-Cdk complex at two sites to inhibit its activity?
Wee1
What activates the M-Cdk complex after all of the phosphorylation events?
Cdk-activating phosphatase
What causes an explosive increase in M-Cdk activity?
Activated M-Cdk indirectly activates more M-Cdk in a positive feedback loop
What regulates the abundance of cyclins?
Protein Degredation by Proteasomes through Ubiquitin Marking
The removal of webbing between fingers and toes during development is due to what cellular process?
Apoptosis
What are the steps of apoptosis?
Cell Shrinks and Chromatin Condenses

Cytoskeleton collapses

Nuclear envelope and other organelle membrane disassemble

DNA breaks up into fragments

Alteration in cell surface and cell fragmenting

Phagocytic cells (macrophages) clean up before cell lysis - avoids cell necrosis
What is the machinery responsible for apoptosis?
Caspase Family of Proteases
What are procaspases?
Inactive precursors of caspase proteases
How are procaspases activated?
Proteolytic cleavage in response to extracellular and intracellular signals
What do most apoptotic pathways target?
Mitochondria
What molecule from the mitochondria binds to an adaptor and ATP to cleave procaspase?
Cytochrome C