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Biology > Chapter 17: Cytoskeleton > Flashcards

Chapter 17: Cytoskeleton Flashcards

1
Q

What are intermediate filaments?

A

Rope like fiber (proteins) that enable cells to withstand mechanical stress that occur when cells are stretch

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2
Q

Where are intermediate filaments found?

A
  1. Desmosomes (cell-cell junction)
  2. Nuclear Lamina (meshwork of intermediate filament within the nucleus)
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3
Q

What makes intermediate filaments so strong?

A

They are like ropes that twist together to provide tensile strength

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4
Q

What generates the rope like structure in intermediate filaments?

A
  1. Coil Coil dimer: two alpha helixes winding around each other
  2. Staggered antiparallel tetramer of two coiled-coil dimers: Two coil-coil dimer coming together in an antiparallel fashion
  3. Lateral association of 8 tetramer
  4. Addition of 8 tetramer to growing filaments
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5
Q

How does intermediate filament strengthen cells against mechanical stress?

A

by distributing the effects of locally applied forces, thereby keeping cells and their membranes from tearing in response to mechanical shear.

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6
Q

What is the nuclear envelope supported by?

A

Nuclear lamina: meshwork of intermediate fillaments

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7
Q

What are lamins?

A

Type of intermediate filament protein that makes up the nuclear lamina

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8
Q

Why are lamin phosphorylation so crucial?

A

They weakened the interaction between filaments, causing the lamina to fall apart for cell division

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9
Q

What were to happen if there is a defect in lamin?

A

progeria—rare disorders that cause affected individuals to age prematurely.

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10
Q

What are microtubules?

A

polymers of tubulin that form part of the cytoskeleton

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11
Q

What are the functions of microtubules?

A

They create a system of track within the cell by

  1. Transporting and positioning organelles within the cell
  2. Guide intracellular transport of cytosolic macromolecules
  3. Assemble into the mitotic spindle during cell division
  4. Form cilia and flagella
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12
Q

How are microtubules structured?

A
  1. α-tubulin and β-tubulin are bound tightly to form a heterodimer
  2. Tubulin dimer stack together to form protofilaments
  3. 13 protofilaments form one microtubulin
  4. Protofilaments come together forming a hollow cylindrical structure
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13
Q

What does it mean for microtubules to have structural polarity?

A

α-tubulin exposed atone end and β-tubulin at the other

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14
Q

Why is it crucial that microtubules have structural polarity?

A

Structural polarity allows for directional intracellular transport

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15
Q

Where do microtubules come from?

A

The centrosome

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16
Q

What is the centrosome’s structure?

A

Matrix of protein surrounding a pair of centrioles

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17
Q

How does nucleation come from the centrosome?

A

The centrosome has nucleating site ( γ tubulin ring complex) which serves as a starting point for the growth of one microtubules.

The αβ-tubulin dimer adds to the + end of the growing microtubules

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18
Q

Why do cells need nucleation site?

A

This allows the cell to control which microtubules to grow from where and how

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19
Q

What does it mean for microtubules to be dynamic instability?

A

microtubules can switch back and forth between polymerization and depolymerization, growing and shrinking ONLY on their + end

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20
Q

Why is dynamic instability crucial to microtubules?

A

Allows it to undergo rapid remodeling to carry their function

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21
Q

When does dynamic instability stop for microtubules?

A

When its plus end is stabilized by attachment to another protein/structure. Thus Microtubules stabilize when
attached to capping proteins

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22
Q

What is dynamic instability driven by?

A

GTP hydrolysis

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23
Q

What side of the microtubules does dynamic instability affect?

A

only + end

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24
Q

How does GTP hydrolysis dictate microtubules assembly and dissembly?

A

Assembly: GTP addition proceeds faster than GTP hydrolysis, forming a GTP cap

Dissembly: GTP hydrolysis is faster than GTP addition

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25
Q

What does microtubules work with to transport cargo?

A

Motor protein

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26
Q

Describe the movement of motor protein?

A

Saltatory movement: small steps with frequent stops

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27
Q

What drives the movement of motor protein?

A

ATP hydrolysis

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28
Q

What are the two types of motor protein?

A
  1. Kinesin
  2. Dynein
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29
Q

What are kinesin?

A

Motor protein that move cargo from minus to plus

30
Q

What are dynein?

A

Motor protein that moves cargo from plus to minus

31
Q

What are the roles of the motor protein body part?

A

Globular head: binds to the microtubules

Tail: binds to cargo

32
Q

How does ATP hydrolysis power dynein/kinesin movement?

A

ATP hydrolysis loosens the binding to microtubule – allows the motors to “walk” along the microtubule

ADP release globular head and ATP bind globular head to microtubules, completing a single step

33
Q

How does the globular head of motor protein contribute to its movement?

A

The globular heads of kinesin and dynein are enzymes
with ATP-hydrolyzing (ATPase) activity.

If the globular head to ATP bound, it is tightly bound to the microtubules. If it is ADP bound, it will loosely bound allowing the motor protein to walk

34
Q

How does microtubules work with the nervous system?

A

determine nerve cell polarity and allow long-distance transport of materials

35
Q

How does microtubules play a role in mitotic division?

A

They attached to the chromosome allowing for chromosome movement

36
Q

Why are Drugs like colchicine and taxol used if they disrupt microtubules polymerization or disassembly?

A

Good for treating cancer

37
Q

What is responsible for the movement of flagella and cillia

A

Dynein

38
Q

What are actin filaments?

A

polymers of the protein actin responsible for the cell’s movement

39
Q

What can actin filaments do when associated with proteins?

A

A. Microvilli – on epithelial cells in the intestine

B. Small contractile bundles – act like muscles inside cells

C. Leading edge of crawling cells – dynamic protrusions to allow movement

D. Contractile ring – pinches the cytoplasm when cells divide

40
Q

What is the structure of actin filaments?

A

twisted chain of identical globular actin
monomers

41
Q

What is common between microtubules and actin filaments?

A

structural polarity, with a plus end and a minus end

42
Q

What is different between microtubules and actin filaments?

A

Microtubules can only grow/shrink on one end

43
Q

How does actin polymerization work?

A

Addition of ATP-bound actin monomers at either end but their rate of growth is faster at the plus end than at the minus end

44
Q

How does treadmilling contribute to actin movement?

A

Actin move when one end of the filament lengthens while the other end shortens. Actin move from plus to minus end

45
Q

What keeps the actin monomers in cells from polymerizing into filaments?

A

thymosin and profilin,

46
Q

What keeps the actin monomers in cells from polymerizing totally into filaments?

A

thymosin and profilin

47
Q

Describe how thymosin and profilin affect actin?

A

preventing actin monomers from adding to the ends of actin filaments

48
Q

What does formins and actin-related proteins (ARPs) do?

A

Promote actin polymerization

49
Q

How does the cell regulate actin filaments

A

Polymerize: formins and actin-related proteins (ARPs)

Prevent Polymerization: Thmosin and Profilin

50
Q

Where is actin most hightly concentrated in the cell?

A

In the cell cortex

51
Q

Why might cell cortex be highly concentrated in actin?

A

For cell crawling and migration to occur

52
Q

How does cell movement work via actin?

A
  1. Cell sends out protrusion, lamellipodia by polymerizing actin on its + end
  2. Protrusions adhere to surface
  3. Rest of the cell drags itself forward
53
Q

What can the interaction between actin and myosin (motor protein) cause?

A

Muscle contraction

54
Q

Describe the structure of myosin

A

Dimer with two globular ATPase heads
One coiled-coil tail

55
Q

What does a cluster of myosin form?

A

Myosin filaments

56
Q

What are myofibrils?

A

contractile elements of muscle cells; extend the length of the cell

“disk on stack”

disk - myofibril
stack of disk - sarcomere

57
Q

What are sarcomeres?

A

contractile unit of myofibril.

Organized assemblies of actin and myosin filaments; they make up myofibril

58
Q

Describe the interaction between myosin and actin filaments

A

the motor activity of myosin moves its head groups along the actin filament in the direction of the plus end.

59
Q

How does the myosin and actin filaments come together?

A

Actin filaments’s + end are anchored to a Z disk while myosin filament overlaps with the - end

60
Q

What happens when there is a muscle contraction?

A

Simultaneous shortening of all the cell’s sarcomeres – due to sliding of the actin filaments past the myosin filaments without change in length

61
Q

Describe the process of muscle contraction

A

Attached: A myosin head binds tightly to an
actin filament (rigor).

Released: Binding of ATP to myosin cause the head to be released from the actin

Cocked: ATP hydrolysis occur, causing a conformational change on the head, which moves the head

Force Generated: The head weakly binds to the actin filaments, releasing the phosphorus from ATP hydrolysis, triggering a conformational change that returns the head to its original shape

Attached: Myosin head binds tightly to the actin filament

62
Q

When does contraction only occur?

A

muscles receive a signal from nerves; spike in Cytosolic Ca2+

63
Q

What signal does a muscle from the nervous to cause it to contract

A

Calcium

64
Q

What does the spike in calcium trigger?

A

actin-myosin contraction through binding of actin-associated proteins

65
Q

What are tropomyosin?

A

rod-shaped protein that overlaps 7 actin monomers,
preventing the binding of myosin to actin.

66
Q

What are troponin?

A

calcium-sensitive complex that binds to tropomyosin.

67
Q

What does troponin do?

A

shifts the position of tropomyosin so that myosin can bind to actin.

68
Q

What happens to troponin when it sense a rise in calcium?

A

It moves tropomyosin from actin so that it can bind to myosin

69
Q

Compare the structure of intermediate filaments and myosin-ii filaments

A

Compare: Bundle

Difference: Intermediate filaments does not have structural polarity, unlike myosin filaments do.

70
Q

What happens when calcium is expelled into the sarcoplasmic reticulum?

A

Muscle relax due to the myosin releasing the actin for the actin to slide back to their original position

Biology (20 decks)

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