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Y1 Cellular Biochemistry and Biology > L11: The Scaffold of the Cell > Flashcards

L11: The Scaffold of the Cell Flashcards

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1
Q

What are the three main components of the cytoskeleton?

A

Actin filaments, microtubules, and intermediate filaments

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2
Q

What is the cytoskeleton’s role in cell structure?

A

It provides shape, support, and resistance to external forces to allow cell migration, division and maintenance, while also enabling dynamic changes in cell structure from environmental changes

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3
Q

What protein forms microtubules?

A

Tubulin, specifically as dimers of alpha and beta tubulin

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4
Q

What are the primary functions of microtubules?

A

Microtubules help maintain cell shape, facilitate movement (like cilia and flagella), organize chromosomes during cell division, and transport cellular cargos

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5
Q

What are the key features of actin filaments?

A

Actin filaments support cell shape, drive cell movement, and are involved in processes like cell adhesion, division, and cargo transport within the cell

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6
Q

What distinguishes actin filaments from microtubules in terms of filament size?

A

Actin filaments are much smaller, about 7 nanometers in diameter, while microtubules are approximately 25 nanometers in diameter

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7
Q

How does actin contribute to cell motility?

A

Actin polymerises at the cell membrane, creating forces that push the cell in the direction of movement

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8
Q

What role do intermediate filaments play in the cytoskeleton?

A

They provide structural stability and resistance to mechanical stress, especially in skin and nerve cells

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9
Q

What role do intermediate filaments play in skin cells?

A

Intermediate filaments composed of keratin provide structural stability to skin cells, helping them withstand external stress and protect underlying tissues

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10
Q

Describe the dynamic instability of microtubules

A

Microtubules grow by adding tubulin dimers and can rapidly disassemble, a process regulated by GTP hydrolysis on tubulin subunits

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11
Q

What is the significance of tubulin isoforms in different cell types?

A

Different tubulin isoforms allow microtubules to interact with unique proteins and fulfill specific functions in various cell types, such as neuron-specific transport functions

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12
Q

How does GTP hydrolysis contribute to the instability of microtubules?

A

GTP hydrolysis in tubulin dimers destabilises microtubules, causing them to disassemble, a process key to their dynamic restructuring

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13
Q

What are microtubule-associated proteins (MAPs)?

A

Proteins that interact with microtubules, helping stabilise them, control their organisation, and link them to other cell structures

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14
Q

How are microtubules organised within cells?

A

They radiate from the microtubule organising center (MTOC), also called the centrosome, which provides a base for rapid microtubule growth

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15
Q

What drugs target microtubules, and what are their uses?

A
  • Drugs like colchicine prevent microtubule polymerisation, and Taxol stabilises microtubules.
  • Both are used in research and some are used clinically, such as in cancer treatments
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16
Q

How does Taxol interact with microtubules, and what is its clinical relevance?

A

Taxol binds to microtubules, stabilizing them and preventing disassembly, which inhibits cell division. It is used in cancer treatment to target rapidly dividing cells

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17
Q

What is the difference between G-actin and F-actin?

A
  • G-actin refers to globular, monomeric actin
  • F-actin is filamentous, polymerised actin forming the actin filaments, arranged in a twisted chain
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18
Q

What are intermediate filaments made from?

A

A variety of proteins, such as keratin, vimentin, and lamin, depending on the cell type and its specific needs

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19
Q

How does the structure of intermediate filaments differ from microtubules and actin filaments?

A

Intermediate filaments are composed of rope-like twisted fibers without polarity, providing strength rather than dynamic motion

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20
Q

What is the role of ATP and GTP in actin and microtubule dynamics?

A

ATP is bound and hydrolysed in actin polymerisation, while GTP is bound and hydrolysed in microtubule dynamics, both providing energy for structural changes

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21
Q

Why is ATP hydrolysis important in actin filament dynamics?

A

ATP-bound G-actin can polymerise into F-actin, and subsequent ATP hydrolysis destabilises F-actin, enabling actin filament turnover

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22
Q

Why are intermediate filaments considered the least dynamic cytoskeletal component?

A

They have low turnover rates and are more stable, primarily providing mechanical support rather than facilitating movement

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23
Q

How does the cytoskeleton differ across cell types and organisms?

A

All eukaryotes have actin, tubulin, and intermediate filaments, but specific types and structures vary by cell type and function

24
Q

What is the effect of actin-binding proteins on actin filaments?

A

They stabilise, organise, or modulate actin filaments, helping form structures like microvilli or enabling cell movement

25
Q

What are protofilaments in the context of microtubules?

A

Protofilaments are linear chains of tubulin dimers arranged head-to-tail, which bundle into a hollow tube to form a microtubule

26
Q

What is the ‘catastrophe’ event in microtubule dynamics?

A

Catastrophe is a rapid disassembly of a microtubule, occurring when GTP bound to tubulin dimers is hydrolysed to GDP, destabilising the structure

27
Q

What is the microtubule organising center (MTOC), and why is it important?

A

The MTOC, or centrosome, contains pre-formed tubulin oligomers and initiates microtubule growth, serving as nucleation sites rapid microtubule assembly when needed

28
Q

How do cilia and flagella use microtubules for movement?

A

Microtubules slide past each other in cilia and flagella to produce beating or whipping motions, driving movement

29
Q

Describe the role of gamma tubulin in microtubule formation

A

Gamma tubulin forms a template within the MTOC that stabilises the start of microtubule growth, helping form a stable nucleation site

30
Q

What cellular process do microtubules assist with during mitosis?

A

Microtubules form the mitotic spindle, which separates chromosomes into daughter cells during cell division

31
Q

Explain the function of the mitotic spindle in cell division

A

The mitotic spindle, formed by microtubules, organises and separates chromosomes into daughter cells during mitosis, ensuring each cell receives a complete set of chromosomes

32
Q

What is the difference between type I and type II microtubule-associated proteins (MAPs)?

A

Type I MAPs bind microtubules at the N-terminus, while type II MAPs bind at the C-terminus, each playing a role in stabilising or organising microtubules

33
Q

How does the drug colchicine affect microtubules?

A

Colchicine binds to tubulin dimers, preventing their addition to microtubules, thereby inhibiting microtubule growth

34
Q

What structural arrangement allows actin filaments to have plus and minus ends?

A

Actin monomers (G-actin) polymerise head-to-tail, creating a structural polarity with distinct plus (barbed) and minus (pointed) ends

35
Q

What is the role of ATP in actin filament polymerisation?

A

ATP binds to G-actin monomers, which then join to form F-actin. ATP is later hydrolysed to ADP, which affects filament stability and dynamics

36
Q

What are some cellular structures that rely on actin filaments?

A

Structures like microvilli, adhesion bands, and contractile rings in dividing cells depend on actin filaments for stability and function

37
Q

Describe the term “microvilli” and the role actin plays in them

A

Microvilli are finger-like projections on some cell surfaces, supported by actin filaments, which increase the cell’s surface area for absorption, such as in intestinal cells

38
Q

What role does phalloidin play in actin dynamics?

A

Phalloidin binds to F-actin, stabilising it and preventing turnover, which can be lethal to cells by halting their structural rearrangements

39
Q

What are intermediate filaments primarily composed of in epithelial cells?

A

In epithelial cells, intermediate filaments are primarily composed of keratin, which provides resilience to mechanical stress

40
Q

How are intermediate filaments structurally distinct from actin filaments and microtubules?

A

Intermediate filaments are rope-like structures made from various proteins, lack polarity, and do not associate with molecular motors, making them less dynamic

41
Q

What is the difference in molecular motors between actin filaments and microtubules?

A

Actin filaments are associated with myosin motors, while microtubules interact with kinesin and dynein motors, each facilitating different types of intracellular transport

42
Q

What is the significance of coiled-coil dimers in intermediate filaments?

A

Coiled-coil dimers provide the basic structural unit, which further assembles into a stable, rope-like filament that resists tension

43
Q

How do intermediate filaments contribute to neural function?

A

Neurofilaments provide structural support for axons, contributing to neuron stability and function in the nervous system

44
Q

What is the primary mechanical advantage of intermediate filaments in cells?

A

Intermediate filaments can deform under stress without breaking, making them ideal for withstanding forces and maintaining cell integrity

45
Q

Why are microtubules considered important for intracellular transport?

A

Microtubules serve as tracks for motor proteins, enabling the transport of vesicles, organelles, and other cargoes within the cell

46
Q

What are some diseases associated with defects in intermediate filaments?

A

Diseases like ALS (Amyotrophic Lateral Sclerosis) and certain skin blistering disorders are linked to issues with neurofilaments and keratin filaments

47
Q

How do microtubules contribute to the function of neuronal cells?

A

In neurons, microtubules provide tracks for transporting cargos along axons and dendrites, supporting cellular communication and function

48
Q

What is the role of actin in the process of phagocytosis?

A

Actin polymerisation helps form membrane extensions that engulf particles, allowing cells to ingest large molecules or pathogens in a process known as phagocytosis.

49
Q

What are lamins, and where are they found?

A

Lamins are intermediate filaments found in the nucleus, providing structural support to the nuclear envelope and helping organise nuclear contents

50
Q

Describe how actin-binding proteins contribute to cell movement

A

Actin-binding proteins regulate the polymerisation and organisation of actin filaments, enabling the cell to push its membrane forward in the direction of movement

51
Q

What is the structural significance of the 13 protofilament arrangement in microtubules?

A

The 13-protofilament arrangement forms a stable, hollow tube that supports cellular shape and enables interactions with motor proteins for transport

52
Q

What causes microtubule ‘catastrophe’ and ‘rescue’ events?

A

Catastrophe occurs when GTP on tubulin is hydrolyzed, leading to disassembly; rescue happens when GTP-bound tubulin is added back, stabilizing and regrowing the microtubule

53
Q

What happens to actin filaments during cell division?

A

Actin filaments form a contractile ring during cytokinesis, pinching the cell into two daughter cells at the end of cell division

54
Q

How do diseases like ALS relate to cytoskeletal components?

A

ALS is associated with defects in neurofilaments (intermediate filaments) that disrupt nerve cell function and lead to progressive muscle weakness

55
Q

Why do cells with high mechanical stress, like skin cells, rely on intermediate filaments?

A

Intermediate filaments provide high tensile strength, allowing skin cells to endure mechanical stress without rupturing

Y1 Cellular Biochemistry and Biology (20 decks)

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