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Biochemistry Exam 3 > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

0
Q

Microtubules are?

A

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

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1
Q

Microfilaments are?

A

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

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2
Q

Function of actin?

A

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

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3
Q

4 examples of actin filaments

A

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

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4
Q

What form is actin in at low concentration?

A

Globular G-actin

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5
Q

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

A

Polymerizes into actin filament with a + and - end

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6
Q

Three phases of actin polymerization

A 
Slow nucleation (just + nuclei)
Fast elongation (both nuclei)
Steady state
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7
Q

T or F: ATP is absolutely necessary for actin polymerization

A

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

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8
Q

What is the actin critical concentration?

A

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

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9
Q

Which end of actin grows faster?

A

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

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10
Q

Example of actin treadmilling

A

Leading edge of moving cells

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11
Q

What is an actin-monomer binding protein?

A

Regulates actin polymerization by binding to free actin molecules

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12
Q

What is thymosin? Profilin?

A

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

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13
Q

How does listeria monocytogenes move inside a cell?

A

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.

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14
Q

What are Arp 2/3?

A

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.

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15
Q

What is gelsonin?

A

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

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16
Q

What is villin?

A

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

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17
Q

What are capping proteins?

A

Cap actin to prevent degredation

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18
Q

How do platelets change shape to clot blood?

A

Drastically increase amounts of F-actin after stimulation

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19
Q

Describe platelet activation

A

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

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20
Q

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

A

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

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21
Q

Name 5 actin cross linking proteins

A

Spectrin, alpha-actinin, filamin, fimbrin, dystrophin

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22
Q

Alpha-actinin forms what?

A

Contractile bundles (muscle)

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23
Q

Fimbrin forms?

A

Parallel bundles that are tight (no myosin)

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24
Q

Filamin forms?

A

Crossed actin fibers

25
Q

Microvilli use what actin cross-linking proteins?

A

Villin or fimbrin. plus end is at tip of microvillus

26
Q

Platelets attach actin to clots via?

27
Q

Actin is connected to muscle ECM by?

A

Dystrophin

28
Q

What type of myosin is in muscle?

29
Q

Describe general structure of myosin

A

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

30
Q

Detail myosin and actin relationship

A

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

31
Q

Structure of myosin II

A

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.

32
Q

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

A

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

33
Q

Functions of actin and myosin II outside of muscle?

A

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

34
Q

What determines the type of myosin?

A

The tail domain

35
Q

Function and description of myosin I?

A

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

36
Q

Function of myosin V?

A

Vesicular transport of secretory vesicles

37
Q

What is tubulin?

A

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

38
Q

Structure of microtubules

A

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

39
Q

Tubulin will polymerize in the presence of?

A

37 degrees C, Mg, GTP

40
Q

Describe the dynamic instability of microtubules

A

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

41
Q

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

A

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

42
Q

Two classes of microtubules

A

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

43
Q

Examples of microtubule function

A

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

44
Q

What are cilia?

A

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

45
Q

Describe axoneme

A

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

46
Q

What is ciliary dyenin?

A

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

47
Q

What are basal bodies?

A

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

48
Q

What is the MTOC?

A

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

49
Q

What is the centrosome?

A

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

50
Q

Function of gamma-tubulin

A

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

51
Q

What is the spindle pole?

A

The MTOC for mitotic spindle (- ends all there)

52
Q

Kinesin motion?

A

From minus end to plus end of microtubule

53
Q

Dynein motion?

A

From plus end to the minus end of the microtubule

54
Q

ER is located where? Golgi?

A

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

55
Q

What are polar microtubules?

A

Microtubules from opposite poles that form the spindle

56
Q

What are Kinetochore microtubules?

A

From centrosome to the kinetochore o the chromosomes

57
Q

What is anaphase A movement?

A

Movement of chromosomes to opposite poles (maybe dynein mediatied)

58
Q

What is anaphase B movement?

A

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

59
Q

How is polar separation achieved via microtubules?

A

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

Biochemistry Exam 3 (11 decks)

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