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cell biology > week 7 the cytoskeleton > Flashcards

week 7 the cytoskeleton Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what are the componets of the cell cytoskeleton

A

actin filaments, microtubules, intermediate filaments

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2
Q

what are actin filaments

A

provides mechanical support, determines cell shape, and allows movement of the cell surface, thereby enabling cells to migrate, engulf particles, and divide.

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3
Q

what are microtubules

A

function both to determine cell shape and in a variety of cell movements, including some forms of cell locomotion, the intracellular transport of organelles, and the separation of chromosomes during mitosis.

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4
Q

What do the daughter cells do after the cell divides?

A

They reorganize their microtubule and actin cytoskeletons into smaller versions of those present in the mother cell, enabling them to crawl their separate ways.

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5
Q

What is bound in the deep cleft at the center of an actin monomer?

A

Either ATP or ADP.

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6
Q

What is the orientation of the subunits within an actin filament?

A

All the subunits within the filament have the same orientation.

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7
Q

What imaging technique is used to visualize an actin filament?

A

Electron micrograph of a negatively stained actin filament

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8
Q

what does the cytoskeleton network do

A

This network is important for cell shape, movement, division, trafficking

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9
Q

what is an actin filament made up of

A

made up an actin monomer which is wither ATP or ADP bound in a deep cleft

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10
Q

what is nucleation

A

the formation of a helical momomer of actin where one actins binds to another which binds to another forming a ‘neclus’ of action

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11
Q

what are the 2 ends that actin is polymerised

A

the minus end which is the slow growing end and the plus end which is the fast growing end

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12
Q

what is treadmilling

A

occurs when one end of a filament grows in length while the other end shrinks, resulting in a section of filament seemingly “moving” across a stratum or the cytosol.

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13
Q

what is profilin

A

binds momoers, concentrates them at sites of filament assembly

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14
Q

what is thymosin

A

binds subunits and prevents assembly

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15
Q

What is the cytoskeleton in a cell?

A

A network of filaments that supports the plasma membrane, gives the cell shape, aids in organelle positioning, provides tracks for vesicle transport, and allows cell movement.

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16
Q

What are the three types of protein fibers in the cytoskeleton of eukaryotes?

A

Microfilaments, intermediate filaments, and microtubules.

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17
Q

What is another name for microfilaments and why?

A

Actin filaments, because they are made of actin monomers

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18
Q

Actin filaments, because they are made of actin monomers

A

Serve as tracks for myosin, involved in cell division, muscle contraction, cargo transport, cell motility, and maintaining cell shape.

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19
Q

How do actin filaments contribute to muscle contraction?

A

Actin and myosin filaments in sarcomeres slide past each other to contract muscles

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20
Q

What is the primary function of intermediate filaments?

A

Maintain cell shape and anchor the nucleus and other organelles in place.

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21
Q

What are microtubules made of?

A

α-tubulin and β-tubulin subunits.

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22
Q

How do microtubules behave dynamically?

A

They can grow and shrink quickly by adding or removing tubulin proteins.

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23
Q

What specialized roles do microtubules play?

A

Provide tracks for motor proteins (kinesins and dyneins) to transport vesicles and cargoes, and form the spindle during cell division to pull chromosomes apart.

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24
Q

how does actin filament grow

A

arp2/3 complexes
-arp2/3 complexes are held together accessory proteins
-when nucleation promoting factor bind they cuse arp2/3 complexes to assemble actin filaments and cause branching

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25
Q

what does proflin do

A

stimulates proflin elongation

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26
Q

What role does profilin play in actin filament elongation?

A

Profilin stimulates actin filament elongation.

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27
Q

What do many nucleation-promoting factors (NPFs) contain?

A

Binding sites for profilin.

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28
Q

What is profilin bound to in the cell?

A

Actin monomers.

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29
Q

What does the activation of NPFs lead to?

A

Nucleation of branched actin filaments by Arp2/3 and rapid elongation of new filaments.

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30
Q

what is the pathway for proflin

A
  • inactive arp2/3 comlexes bind to nucleation promoting factors (NPFs)
    this causes actin momers to bind and nucleate actin filament
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31
Q

What is the composition of a myosin II molecule?

A

Two heavy chains and four light chains.

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32
Q

How many types of light chains are present in a myosin II molecule?

A

Two distinct types, with one copy of each type present on each myosin head.

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33
Q

What causes the dimerization of myosin II?

A

The two α helices of the heavy chains wrap around each other to form a coiled-coil, driven by the association of regularly spaced hydrophobic amino acids.

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34
Q

What structure does the coiled-coil arrangement of myosin II heavy chains form?

A

An extended rod in solution, which forms the tail of the myosin II molecule.

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35
Q

Describe the structure of a microtubule.

A

A microtubule is a stiff hollow tube formed from 13 protofilaments aligned in parallel.

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36
Q

How is the GTP molecule associated with the β-tubulin monomer?

A

It is less tightly bound and plays an important role in filament dynamics

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37
Q

What is the function of γ-TuRC?

A

Nucleates microtubule assembly and remains associated with the minus end, forming a centrosome near the nucleus.

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38
Q

Where is γ-TuRC located and what does it form?

A

Located next to the nucleus in the cytosol, forming a centrosome.

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39
Q

What is the role of γ-tubulin in cells?

A

Promotes the formation of new microtubules

40
Q

What is the primary function of katanin?

A

Severs microtubules.

41
Q

How does katanin contribute to microtubule dynamics

A

Promotes complex reorganization of the microtubule array by severing microtubules.

42
Q

How does microtubule organization differ in other cell types

A

More complex distributions of microtubule plus and minus ends are observed.

43
Q

What direction do kinesin and dynein transport cargo along microtubules?

A

Kinesin transports towards the plus-ends, while dynein transports towards the minus-ends of microtubules.

44
Q

Describe the structure of kinesins.

A

Kinesins consist of two heavy chains (heads) that interact with microtubules, joined by a middle domain to two light chains (tails) where the cargo binds

45
Q

What is the function of kinesins?

A

Kinesins function in vesicular transport

46
Q

How do kinesins move?

A

Kinesins use ATP to fuel their movement, with the ATP-lagging head detaching, passing over the ADP-leading head, and attaching at the next binding site.

47
Q

How do dyneins bind to cargo

A

Dyneins need an adaptor protein called dynactin to bind to cargo.

48
Q
A
49
Q

What are the similarities between kinesins and dyneins

A

Both kinesin and dynein move along microtubules, can engage with cargo, and use ATP to fuel their movements

50
Q

What are the differences between kinesins and dyneins?

A

Kinesin moves towards the plus-end and binds directly to cargo via light chains, while dynein moves towards the minus-end and binds to cargo via dynactin. Dynein typically moves faster than kinesin.

51
Q

Describe the structure of intermediate filaments.

A

Monomers pair to form a coiled dimer, two dimers form an antiparallel tetramer, and tetramers pack together in a rope-like array to provide mechanical strength to cells.

52
Q

Why is cell polarity important during early development

A

ensures that the inside is on the inside and the outside is on the outside, particularly important during the formation of the epithelial sheet and gastrulation.

53
Q

What is the effect of activating the small GTPase Rac on actin organization?

A

It promotes the formation of protrusive actin networks in lamellipodia and pseudopodia through alterations in actin accessory proteins.

54
Q

How does Rac-GTP activate actin nucleation?

A

Rac-GTP activates members of the WAVE protein family, which then activate actin nucleation and branched network formation by the Arp2/3 complex.

55
Q

Describe the parallel pathway involving Rac-GTP and PAK.

A

Rac-GTP activates PAK, which inhibits myosin light-chain kinase (MLCK) through phosphorylation, leading to myosin II filament disassembly and decreased contractile activity.

56
Q

: What is the overall result of Rac activation on actin networks and contractility

A

Rac activation leads to branched actin networking in cellular protrusions and less contractility and stress fibers.

57
Q

What does activation of the GTPase Rho lead to in terms of actin organization?

A

increases contraction by myosin II

58
Q

What are the effects of Rho activation on cellular structures

A

Rho activation increases contractility, stress fibers, and focal adhesion formation.

59
Q

How do neutrophils achieve polarization and chemotaxis?

A

Binding of bacterial molecules to G-protein-coupled receptors stimulates directed motility, with receptors more likely bound to bacterial ligands at the front.

60
Q

What are the two signaling pathways involved in neutrophil polarization?

A

1) The Rac pathway
The Rho pathway

61
Q

what is the key objective of cell division

A

key objective of cell division is to provide each daughter cell with exactly the same genetic information as the parent cell

62
Q

What are the four stages of the cell cycle?

A

Gap phase 1 (G1), Synthesis phase (S), Gap phase 2 (G2), and Mitosis (M).

63
Q

What is G0?

A

A resting state where a cell may temporarily, indefinitely, or permanently exit the cell cycle.

64
Q

What are the three checkpoints in the cell cycle?

A

G1, S, and G2.

65
Q

What happens during Gap phase 1 (G1)?

A

Cells grow in size, producing organelles, cytoskeleton, and some DNA and proteins needed for DNA synthesis.

66
Q

What is interphase?

A

The collective term for G1, S, and G2 phases.

67
Q

What occurs during cytokinesis?

A

Cytoplasmic division.

68
Q

What is M phase?

A

The combination of mitosis and cytokinesis.

69
Q

: What occurs during Gap phase 2 (G2)?

A

Cells grow in size and produce required proteins, and there is a checkpoint to confirm readiness to enter M phase.

70
Q

What happens during the Synthesis phase (S)?

A

DNA synthesis to duplicate chromosomes.

71
Q

How is the cell cycle controlled in eukaryotic cells?

A

egulatory proteins specified by cdc genes

72
Q

What happens at the cell cycle checkpoints?

A

halts progression, initiates corrective measures, or aborts the cycle if deficiencies are detected.

73
Q

What is the consequence of the cell cycle continuing when it shouldn’t?

A

Abnormal and unrestrained proliferation, which is a critical feature of cancer cells.

74
Q

How can certain drugs affect the cell cycle?

A

They can cause the cell cycle to arrest in G1 or G2/M by affecting proteins involved in checkpoint mechanism

75
Q

What is checked during the G2 phase?

A

The accuracy of DNA replication is thoroughly checked.

76
Q

What are Cyclin and CDK complexes?

A

Key components of the cell cycle control system that regulate the cycle by forming protein kinase complexes.

77
Q

How do Cyclin-CDK complexes function?

A

When cyclin forms a complex with Cdk, the protein kinase is activated to trigger specific cell-cycle events.

78
Q

What happens if Cyclin is absent?

A

Cdk is inactive without Cyclin.

79
Q

What are the different Cyclins active at different times?

A

G1/S CDK, S/CDK, and M-CDKs

80
Q

What blocks the active site of CDK in its inactive state?

A

The T-loop region of the protein blocks the active site.

81
Q

What effect does cyclin binding have on CDK?

A

Cyclin binding causes the T-loop to move out of the active site, partially activating CDK2.

82
Q

How is CDK2 further activated after cyclin binding?

A

Phosphorylation of CDK2 at a threonine residue in the T-loop by CAK changes the shape of the T-loop, improving the enzyme’s ability to bind its protein substrates.

83
Q

What are the two mechanisms of CDK inhibition?

A

Phosphate addition by kinase and binding of CDK inhibitory protein (CKI)

84
Q

What happens to polyubiquitylated target proteins?

A

They are recognized and degraded in a proteasome.

85
Q

How does DNA polymerase move along the template strand?

A

DNA polymerase proceeds in the 5’-to-3’ direction along the template strand.

86
Q

What is the difference between leading strand and lagging strand synthesis?

A

Leading strand synthesis is continuous, while lagging strand synthesis is discontinuous, producing Okazaki fragments that are later joined together

87
Q

What key events occur during Prophase in mitosis?

A

Chromatin condenses into visible chromosomes.
Each chromosome consists of two sister chromatids joined at the centromere.
The mitotic spindle begins to form, originating from the centrosomes.
The nucleolus disappears.

88
Q

What happens during Prometaphase in mitosis?

A

The nuclear envelope breaks down.
Microtubules from the mitotic spindle attach to kinetochores on the centromeres of chromosomes.
Chromosomes begin to move toward the cell’s equator

89
Q

Describe the events of Metaphase in mitosis.

A

Chromosomes align at the metaphase plate (the cell’s equatorial plane).
The kinetochores of sister chromatids attach to microtubules from opposite spindle poles.

90
Q

What occurs during Anaphase in mitosis?

A

Sister chromatids are pulled apart as the microtubules shorten.
The separated chromatids, now individual chromosomes, are pulled to opposite poles of the cell.
The cell elongates as non-kinetochore microtubules lengthen

91
Q

What key processes happen during Telophase in mitosis

A

Chromosomes reach the opposite poles and begin to de-condense back into chromatin.
The nuclear envelope re-forms around each set of chromosomes.
The nucleolus reappears.
The mitotic spindle disassembles.

92
Q

what do Kinetochores

A
  • Kinetochores control the movements of chromosomes during cell division. Sister chromatids are positioned by the kinetochores, which face in opposing directions and attach to the mitotic spindle.
93
Q

what is the metaphase to anaphase checkpoint

A

Ensures proper alignment of all chromosomes before anaphase.

94
Q

what is the mechanism for metaphase tp anaphase checkpoint

A

Uses APC/C (Anaphase-Promoting Complex) for marking proteins for degradation.
APC/C Function: Targets M-cyclins and triggers breakdown of the cohesin complex holding sister chromatids together.

95
Q
A

cell biology (8 decks)

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