Cytoskeleton

Question 0

Microtubules are?

Answer 0

25 nm in diameter. Major component is tubulin. Much more rigid than actin.

Question 1

Microfilaments are?

Answer 1

6 nm in diameter. Major component is actin. G-actin is globular. F-actin is filament

Question 2

Function of actin?

Answer 2

Associated with plasma membrane to determine the topology and is connected with the cellular functions of the membrane

Question 3

4 examples of actin filaments

Answer 3

Microvilli
Stress fibers
Lamellipodia and filopodia for moving cell
Contractile ring during cell division

Question 4

What form is actin in at low concentration?

Answer 4

Globular G-actin

Question 5

In presence of ATP or ADP, as you increase actin concentration what happens?

Answer 5

Polymerizes into actin filament with a + and - end

Question 6

Three phases of actin polymerization

Answer 6

Slow nucleation (just + nuclei)
Fast elongation (both nuclei)
Steady state

Question 7

T or F: ATP is absolutely necessary for actin polymerization

Answer 7

F, can work in presence of ADP too just different kinetics

Question 8

What is the actin critical concentration?

Answer 8

Minimal G-actin concentration needed for polymerization to occur. Above this concentration, you get mix of polymers and free subunits, below just free subunits.

Question 9

Which end of actin grows faster?

Answer 9

Grow faster at + end than the - end. Critical concentration is lower at the + end than the - end. Can lead to a process known as treadmilling

Question 10

Example of actin treadmilling

Answer 10

Leading edge of moving cells

Question 11

What is an actin-monomer binding protein?

Answer 11

Regulates actin polymerization by binding to free actin molecules

Question 12

What is thymosin? Profilin?

Answer 12

Thymosin is a actin-monomer binding protein. Profilin is antagonist to thymosin and promotes actin polymerization

Question 13

How does listeria monocytogenes move inside a cell?

Answer 13

Recruits actin in the cell and polymerizes behind itself. Pushes the bacterium around using profilin. Can move fast enough to make a microvilli out of the host cell.

Question 14

What are Arp 2/3?

Answer 14

Two actin related proteins that can catalyze the nucleation and polymerization of actin. Similar to the + end of actin. Binds to the minus end and encourages elongation at the + end of polymer.

Question 15

What is gelsonin?

Answer 15

Caps the plus end of actin and severs it. Ca+2 mediated. From macrophages

Question 16

What is villin?

Answer 16

Ca+2 activated F-actin severing protein. From intestine

Question 17

What are capping proteins?

Answer 17

Cap actin to prevent degredation

Question 18

How do platelets change shape to clot blood?

Answer 18

Drastically increase amounts of F-actin after stimulation

Question 19

Describe platelet activation

Answer 19

Controlled sequence of actin filament severing, uncapping, elongation, recapping, and cross-linking of actin (mediated by Ca+2 and PIP2)

Question 20

What are the general characteristics of F-actin cross linking proteins?

Answer 20

Two F-actin binding sites. The length and flexibility of the crosslinking protein determines whether bundles or networks are formed

Question 21

Name 5 actin cross linking proteins

Answer 21

Spectrin, alpha-actinin, filamin, fimbrin, dystrophin

Question 22

Alpha-actinin forms what?

Answer 22

Contractile bundles (muscle)

Question 23

Fimbrin forms?

Answer 23

Parallel bundles that are tight (no myosin)

Question 24

Filamin forms?

Answer 24

Crossed actin fibers

Question 25

Microvilli use what actin cross-linking proteins?

Answer 25

Villin or fimbrin. plus end is at tip of microvillus

Question 26

Platelets attach actin to clots via?

Answer 26

Filamin

Question 27

Actin is connected to muscle ECM by?

Answer 27

Dystrophin

Question 28

What type of myosin is in muscle?

Answer 28

Myosin II

Question 29

Describe general structure of myosin

Answer 29

Head, neck, tail domains. Tail domain provides myosin with distinct function

Question 30

Detail myosin and actin relationship

Answer 30

Myosin heads walk down the actin filament towards the + end using ATP for each step.

Question 31

Structure of myosin II

Answer 31

Two heavy chains and four light chains. Heavy chains have heads with ATPase activity Dimerization occurs into a coil-coil structure of two alpha-helical tails.

Question 32

T or F: The polarity of the myosin filament is reversed at the M-line in the sarcomere

Answer 32

T (in order for the myosin to walk toward the plus ends of the actin at the z-disk)

Question 33

Functions of actin and myosin II outside of muscle?

Answer 33

Contractile ring, stress fibers in fibroblasts, adhesion belts in epithelial cells.

Question 34

What determines the type of myosin?

Answer 34

The tail domain

Question 35

Function and description of myosin I?

Answer 35

One headed, moves vesicles around the cell, attaches to plasma membrane. Links with actin bundles in microvilli.

Question 36

Function of myosin V?

Answer 36

Vesicular transport of secretory vesicles

Question 37

What is tubulin?

Answer 37

Heterodimer of two closely related subunits. Alpha and beta tubulin.

Question 38

Structure of microtubules

Answer 38

Tubulin heterodimers packed around central core. 13 protofilaments aligned in parallel making the structure polar. Fast growing + end and slow growing - end.

Question 39

Tubulin will polymerize in the presence of?

Answer 39

37 degrees C, Mg, GTP

Question 40

Describe the dynamic instability of microtubules

Answer 40

GTP on beta-tubulin causes for the formation of straight filament polymers. GTP hydrolysis weakens the bond in the polymer and can lead to depolymerization in order to exchange GDP for GTP

Question 41

T or F: GTP hydrolysis lags behind polymerization in microtubule formation

Answer 41

T, two classes those with GTP caps or ones that are all GDP

Question 42

Two classes of microtubules

Answer 42

GTP cap - growth GDP - disassembly Capping proteins can be used to prevent GDP destabilization

Question 43

Examples of microtubule function

Answer 43

Cytoplasmic microtubules in interphase Mitotic spindle Structure microtubules in cilia and flagella

Question 44

What are cilia?

Answer 44

Hair like appendages with bundles of microtubules at core. Contain the axoneme.

Question 45

Describe axoneme

Answer 45

9+2 model. 9 doublets, one complete ring and one partial, 11 subunits. 2 center full 13 subunit microtubules

Question 46

What is ciliary dyenin?

Answer 46

Drives bending motion in the axoneme. Walks toward the minus end of tubule.

Question 47

What are basal bodies?

Answer 47

Lower portion of the axoneme. Composed of 9 sets of triplet microtubules (1 full, 2 incomplete). Centriole have same form as the basal body.

Question 48

What is the MTOC?

Answer 48

Polymerization centers. Nested minus end and plus end growing out.

Question 49

What is the centrosome?

Answer 49

A MTOC with many copies of gamma-tubulin in a ring complex, template for the 13 protofilaments. Shaped in L-shape configuration. Duplicate and split to opposite sides of cell when mitosis begins

Question 50

Function of gamma-tubulin

Answer 50

Associates with the alpha-tubulin to form ring. Template for the microtubule 13 protofilaments

Question 51

What is the spindle pole?

Answer 51

The MTOC for mitotic spindle (- ends all there)

Question 52

Kinesin motion?

Answer 52

From minus end to plus end of microtubule

Question 53

Dynein motion?

Answer 53

From plus end to the minus end of the microtubule

Question 54

ER is located where? Golgi?

Answer 54

Align with microtubules and extend almost to end of cell, requires kinesin Golgi near the centrosome, requires dyenin

Question 55

What are polar microtubules?

Answer 55

Microtubules from opposite poles that form the spindle

Question 56

What are Kinetochore microtubules?

Answer 56

From centrosome to the kinetochore o the chromosomes

Question 57

What is anaphase A movement?

Answer 57

Movement of chromosomes to opposite poles (maybe dynein mediatied)

Question 58

What is anaphase B movement?

Answer 58

Sliding of polar microtubules against each other to separate the poles (kinesin mediated)

Question 59

How is polar separation achieved via microtubules?

Answer 59

Four headed kinesin walks toward plus end of tubules and pushes apart the two spindle poles. Dynein walks along the cell cortex from the plus to minus end of astral microtubules