Cytoskeleton and cell junctions

Question 1

Cell-cell junctions and functions

Answer 1

Anchoring junctions: anchor the cytoskeleton
(adherins & desmosomes)

Occluding junctions: prevents the passage of small molecules

Communicating junctions: passes cellular material between cells

Question 2

Anchoring junction proteins and attachment

Answer 2

Cadherins = cell-cell attachment

Integrins = cell-matrix attachment

Question 3

Extracellular cadherin binding

Answer 3

Homophilic binding occurs through Knobs and Pockets interaction between N termini

Ca2+ binds to hinge regions between EC domains and keeps the cadherin rigid for binding

Multiple cadherins binding in parallel form strong adherin junction

Question 4

Cell-matrix junctions and functions

Answer 4

Anchoring junctions: anchor the cytoskeleton
(focal adhesions & hemidesmosomes)

Question 5

Cytoskeletal filaments and functions

Answer 5

Actin filament: control cell shape

Intermediate filament: mechanical stability

Microtubules: Position organelles, transport network

Question 6

Categories of cell cycle regulation

Answer 6

Cyclin & Cdk complex formation

Activation of Cdk by phosphorylation via CAK

Inhibition of Cdk by phosphorylation via Wee 1

Binding of Cdk inhibitors

Question 7

Cyclin-Cdk complexes to relevant phase

Answer 7

G1 - Cyclin D, Cdk 4/6

G1 > S - Cyclin E, Cdk 2

S - Cyclin A, Cdk 1/2

G2 > M - Cyclin B, Cdk 1

Question 8

Actin structure

Answer 8

Double stranded, polar, thinnest filament

g-actin (globular sub units) form f-actin (filament)

Question 9

F-actin kinetics

Answer 9

Cc: steady state concentration

Kon/off: g-actin addition/dissociation

Treadmilling: Kon = Koff, actin moves in one direction

Question 10

Cytoskeleton motor proteins

Question 11

Microtubule structure

Answer 11

Hollow cylinder composed of tubulin, polar, thickest filament,

Ring of 13 adjacent longitudinal protofilaments

Question 12

MTOC (centrosome) composition

Answer 12

Pair of centrioles at 90°

Pericentriolar material

γ-TuRC - nucleation sites (+ end nucleates, - end anchored)

Question 13

Filament-associated motor proteins

Answer 13

Actin: Myosin - skeletal muscle action

Microtubule (intracellular transport) :

Kinesin - movement toward + end (Anterograde)
Dynein - movement toward - end (Retrograde)

Question 14

Method for movement of microtubule-associated motor proteins

Answer 14

Association and dissociation of phosphate from strong ATP-bound lagging head on microtubule to weak ADP leading head. Cause lagging head to move over and forwards.

Question 15

Intermediate filament structure

Answer 15

2 monomer coil into a dimer. Adjacent dimer staggered binding to form tetramer. Series of 8 lateral tetramers form filament

Non-polar

Many types of IF

Question 16

Cadherin structure (Terminus)

Answer 16

C-terminus: bind to cytoskeleton

N-terminus: bind to cadherin (for homophilic adhesions)

Question 17

Are all cadherin’s single pass transmembrane proteins?

Answer 17

Yes, except for flamingo

Question 18

Intracellular cadherin binding

Answer 18

Binding to cytoskeleton is indirect

Cadherin binds to f-actin via adaptor protein, catenin

Called an adherin junction

Question 19

How is an adhesion belt formed?

Answer 19

Adheren junction is formed. More cadherins recruited, actin treadmill to expand junction.

Question 20

What filament do desmosomes link cadherins to?

Answer 20

Intermediate filament