Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BB10005 COPY > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

What is the cytoskeleton?

A
  1. Network of protein filaments throughout the cytoplasm and in the nucleus
  2. Important for supporting a large volume of cytosol
  3. Highly dynamic
  4. Responsible for cell shape and movement
  5. Made from protein sub-units (monomers)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are some of the functions of the cytoskeleton?

A
  1. Mitosis
  2. Cytokinesis
  3. Traffrick- think involved but don’t know exact role
  4. Support
  5. Sperm to swim- flagella
  6. White blood cells to crawl
    7 Muscle contraction
  7. Formation of axons/dendrites
  8. Cell shape
  9. Growth of plant cell wall
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the three types of cytoskeletal filament?

A
  1. Intermediate filaments
  2. microtubules
  3. actin filaments.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the size of intermediate filaments?

A

10nm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the size of microtubules?

A

25nm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the size of actin filaments?

A

7nm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the roles of the intermediate fibres?

A

Provide tensile strength for cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What types of cells are intermediate fibres particularly abundant mean?

A
  1. Cells that are subject to mechanical stress such as muscle cells or epithelial cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How do intermediate filaments form in cells?

A
  1. They form a network throughout the cytoplasm, surround the nucleus and extend out to the cell periphery.
  2. They are often anchored at the plasma membrane cell junctions.
  3. 6) No polarity- look same in either direction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the three main classes that intermediate filaments can be grouped into?

A
  1. Keratin filaments- epithelial cells
  2. Vimentin and vimentin related filaments- connective tissue cells, muscle cells and supporting cells of nervous tissue (neuroglial cells)
  3. Neurofilaments- in nerve cells
  4. Also nuclear lamins- in all nucleated cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How are intermediate filaments constructed?

4) A lot of contact so a strong stable structure
5) Two dimers line up to form a staggered tetramer
a) N terminus of different dimers at opposite ends
6) Tetramers pack together end to end-because of attractive N and C terminus
7) 8 tetramers are twisted into a rope of diameter approx. 10 nm
a) Good mechanical strength

A
  1. They are made up of monomers with a central rod domain
  2. globular N and C terminus region at either end.
  3. The monomers dimerize and the helix coil around each other- forms coiled-coil dimer
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How are all of the cytoskeletal structures constructed?

A
  1. Smaller protein subunits oligomerise (join together) to form filaments.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the monomers that make up intermediate filaments?

A
  1. Globular N and C termini with a long alpha-helical region in between.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What do the alpha helices in intermediate filaments made up of?

A
  1. around 320 amino acids- 48 nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the name of the structure that is formed when the two monomers of intermediate filaments dimerize?

A

Coiled-coil dimers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where is the N terminus found and what is it made up of?

A

At the start of the polypeptide chain, it is an amino group.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Where is the C terminus found and what is it made up of?

A

At the end of the polypeptide chain. It is a carboxy group.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What happens after the dimers are formed in the formation of intermediate filaments?

A
  1. Two line up to form a staggered tetramer.

2. N terminus of different dimers at opposite ends

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What happens after the tetramers are formed in the formation of intermediate fibres?

A
  1. Tetramers pack together end to end-because of attractive N and C terminus
  2. 8 tetramers are twisted into a rope of diameter approx. 10 nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the diameter of the rope structure that is formed by the tetramers in intermediate fibres?

A

10nm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are keratins and what do they do?

A
  1. They are a type of intemediate filament found in the epithelia that span the interior from one side to the other.
  2. They indirectly connect to filaments of other cells through cell-cell junctions that are called desmosomes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How do keratins connect to filaments of other cells?

A
  1. Cadherins make contact with cadherins of another cell
  2. Cadherins span the two membranes and bind the 2 cells together
  3. So Filaments are indirectly in contact with each other
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are cadherins?

A
  1. Transmembrane proteins that span the bilayer and interact with plaque proteins on the cytosolic side of membranes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Why does keratin indirectly link cells together?

A
  1. Filaments attach to plaque proteins which attach to integral membrane proteins- cadherins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is an example of an intermediate filament disorder?

A
  1. Epidermolysis bullosa simplex
  2. Rare genetic disorder
  3. Keratin cannot form normal filaments in the epidermis
  4. Skin is highly susceptible to mechanical injury
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What benefits do intermediate filaments provide?

A
  1. Allow stress to skin- it can stretch and barrier won’t be broken
  2. Cells would ruptured under mechanical stretch with no filaments
  3. Are extremely stable, strong and durable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is nuclear lamina?

A
  1. Intermediate filaments that lie beneath the nuclear membrane.
  2. They are extracellular matrix proteins.
  3. Give nucleus its shape
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What provides the stability of intermediate filaments?

A
  1. They have extensive protein-protein contacts.

2. The individual contacts are not strong, but when all put together they are.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What cells are actin filaments found?

A

In all eukaryotic cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the diameter of actin filaments?

A

7nm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are actin filaments made up of?

A
  1. Globular monomers that associate head to tail.
  2. Two lobes and deep cleft where ATP sits
  3. They are unstable without associated proteins.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How are the actin filaments formed?

A
  1. G-actin- monomer on its own
  2. F-actin- monomer associates with other monomers
  3. G-actin forms G-ACIN (filament) in the presence of ATP Mg and K
  4. Concentration of G-actin is critical- needs to be high enough
  5. Above the critical concentration (Cc) of G-actin the molecules will polymerise
  6. Below critical concentration the actin filaments will depolarise
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is special about the growth of actin/polymerisation?

A
  1. ATP is carried by actin monomers that is hydrolysed to ADP after assembly into the filament
  2. but the monomer is less stable when ADP is bound. 3. The ADP cannot be exchanged for ATP until the monomer disassembles
  3. The monomer will be released from the chain and can regain ATP and join again.
  4. The actin chain is continually being added to and degraded.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

In test tube actin filament polymerisation experiment

A
  1. Start with high concentration of actin subunits and ATP- nucleation lag phase
  2. Salt added- starts the assembly of actin filaments- elongation growth phase
  3. Get to phase where actin filaments no longer want to increase in length as concentration of G-actin falls to critical concentration
  4. so addition of new monomers to actin filament is balanced by removal of monomers- steady state (equilibrium phase)
  5. Actin subunits in filaments over time after salt addition- s-shaped curve
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What happens when the concentration of the monomeric actin drops?

A

The rate of disassembly equals the rate of polymerisation. There is no net growth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What is difference between actin filaments and intermediate filaments?

A
  1. Actin filaments have polarity whereas intermediate filaments do not.
  2. Assembly is not one on top of other
  3. Slight on sides so results in slight spiral
  4. One end can be distinguished from the other
  5. Negative contains ATP binding cleft
  6. Plus end- dome of actin monomer is exposed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What are some of the proteins that might bind to actin to modify its properties?
1) Formation of actin filaments is highly regulated as in cell G-actin concentration is way above Cc so need to be regulated so aren’t constantly formed- small GTPase regulates

A
  1. Monomer binding proteins- Thymosin prevents actin monomers assembling into filaments
  2. nucleating protein- Determines where the actin filaments start to assemble
  3. cross-linking proteins- Network of actin filaments can form
  4. bundling proteins- To give bundles of filaments
  5. motor proteins- Move along actin filaments and due to directionality of actin filaments they move in certain directions
  6. Capping proteins- Stabilise filaments
38
Q

What are some of the drugs that act on the actin cytoskeleton and what they do?

A
  1. Cytochalasin D binds to the positive end of F-actin and prevents further addition of G-actin.
  2. Phalloidin (from poisonous mushroom) binds to F-actin and prevents actin filaments from depolymerising.
39
Q

What are the functions of actin?

A
  1. Mechanical strength and cell shape
  2. cell crawling
  3. muscle contraction
  4. organelle movement.
40
Q

Where is actin usually found?

A

In a layer just below the plasma membrane.

41
Q

How are actin filaments linked into a meshwork?

A

Actin binding proteins.

42
Q

What is the function of cortical actin?

A

Provide mechanical strength and cell shape.

43
Q

What is cell crawling and how does it work?

A
  1. Cells use internal contractions to pull itself forward due to extensions of the plasma membrane called filopodia/lammelipodia.
44
Q

What is the mechanism of cell crawling with lammelipodium?

A
  1. Extensions called filopodia or lamellipodia extend a region of plasma membrane- caused by formation of actin filaments under plasma membrane
  2. Integrins adhere to extracellular matrix- acts as anchor point
  3. Cells use internal contractions to pull itself forward
  4. Plasma membrane is formed and sends out a projection, it grabs onto the extracellular matrix via proteins called integrins- firm anchor
  5. C Contraction at the opposite end of the cell pushes the cell forward- requires cytoskeletal rearrangement
  6. If a filopodia is sent out and there is no attachment it will just contract back onto itself
45
Q

What provides the energy to move actin filaments?

A
  1. Myosin, which is an actin-dependent motor protein that move along actin filaments
  2. It can bind and hydrolyze ATP to provide energy for the movement of the actin filament.
  3. There are many different types of myosin (humans have 40 myosin genes).
  4. Myosin II is the myosin found abundantly in muscle.
46
Q

In what direction to myosins move?

A
  1. From the negative end to the positive end of actin filaments.
  2. The exception is myosin VI which moves from + to -.
47
Q

What is the first stage in the cycle of myosin heads and actin filaments?
a) at the beginning of the cycle the myosin head lacks nucleotide (ATP) and is locked onto the actin filament in the rigor position.

A
  1. The myosin head lacks ATP and is locked onto the actin filament- in the rigor position
  2. Rigor mortis (the rigidity of death) is caused by this locking of myosin onto actin filaments (due to lack of ATP production when dead).
  3. In living cells this position is very short lived as there is a lot of ATP in cells.
48
Q

What is the second stage in the cycle of the myosin head and actin filaments?

A
  1. ATP binds and a conformational change occurs.
  2. The affinity of the myosin for the filament is reduced.
  3. Myosin is released from the actin
49
Q

What is the third stage in the cycle of the myosin head and actin filaments?

A

When ATP is hydrolysed to ADP + Pi (which remain bound to myosin) a large conformational change occurs that causes the head to be displaced along the filament.

50
Q

What is the final stage in the cycle of the myosin head and actin filaments?

A
  1. A weak binding to actin filament (at a new site) causes the release of inorganic phosphate and tight binding to the actin.
  2. The release triggers the power stroke in which the head regains its original (rigor) conformation and releases the bound ADP.
  3. The myosin is bound to a different actin molecule (two units away) from the initial binding.
51
Q

What happens to the Z discs in muscle contraction?

A
  1. In muscle contraction the filaments do not shorten.
  2. They move relative to one another.
  3. The myosin heads ‘walk’ towards the plus ends of the actin filaments pulling the z-discs closer together.
52
Q

What are microtubules?

A
  1. Long, hollow cylinders made up of tubulin monomers. 2. They are more rigid and straight than intermediate filaments or actin filaments.
  2. Approximately 25 nm in diameter
53
Q

How do microtubules form?

A
  1. They grow out from a microtubule organising centre (MTOC).
54
Q

What is an example of a MTOC?

A
  1. Centrosomes in animal cells.
55
Q

Do microtubules have structural polarity?

A
  1. Yes.
56
Q

What are the two types of tubulin?

A

1 Alpha and beta.

57
Q

How does the tubulin arrange to form the microtubules?

A
  1. Made up of a dimer of alpha and beta tubulin
  2. These are held together by non-covalent interactions but the interaction is very strong
  3. Subunits stack together to form a hollow cylindrical microtubule
58
Q

How many subunits make up the circumference of the microtubule?

A

13.

59
Q

What tubulin is exposed at the positive end of a microtubule?

A

Beta tubulin.

60
Q

What is a microtubule subunit?

A
  1. A subunit made up of one alpha tubulin and one beta tubulin.
61
Q

How do the subunits add to the positive end of the microtubule?

A
  1. The alpha unit binds to the exposed beta unit to create a structure with another exposed beta unit.
  2. Subunits are assembled into the growing tube individually to make up the tube.
  3. They don’t assemble into individual filaments which then associate to form the tube.
62
Q

What is the difference between bound GTP in alpha and beta tubulin?

A
  1. Alpha tubulin ATP provides a structural function to the molecule
  2. whereas the beta tubulin can by hydrolysed after assembly.
63
Q

What is dynamic instability?

A
  1. When microtubule are constantly assembled and deassembled.
64
Q

Where is the centrosome located?

A
  1. The centre of cells
  2. Minus ends of microtubules are anchored at the centrosome with plus ends extending out towards the periphery of the cell.
65
Q

What forms a centrosome?

A
  1. A cylindrical arrangement of 9 microtubules (gamma tubulin)
  2. with 2 partial microtubules attached.
  3. The gamma tubulin rings act as nucleating centres for microtubules to grow out from.
66
Q

What determines the growth of microtubules?

A

GTP hydrolysis.

67
Q

What happens if new subunits are faster than beta tubulin hydrolyses GTP?

A
  1. A GTP cap will form which allows the microtubule to continue growing.
  2. When a GTP cap is present the microtubule end is stable and can continue to grow.
  3. GTP hydrolysis normally occurs after the beta subunit is added
68
Q

What happens if GTP is hydrolysed faster than new subunits are added?

A
  1. The GTP cap is lost.
  2. GDP bound beta-tubulin has a different conformation to GTP bound and there are weaker interactions with the neighbouring subunits in the filament.
  3. The ends disassemble, causing rapid shrinkage of the microtubule.
  4. A shrinking microtubule may suddenly start to grow again.
69
Q

What is the name for rapid shrinkage of a microtubule end?

A
  1. Catastrophe.
70
Q

How could a shrinking microtubule start to grow again?

A
  1. GTP islands along the lengths of the microtubules could allow this.
71
Q

What can prevent dynamic instability of microtubules?

A
  1. Interacting proteins.
72
Q

What are the functions of microtubules?

A
  1. Cellular organisation, movement of organelles, cell polarity
  2. Cell division, mitosis, meiosis
  3. Cilia and flagella
73
Q

What are the motor proteins involved in microtubules?

A

Kinesins and dyneins.

74
Q

What motor proteins move towards the positive end of microtubules?

A

Kinesins.

75
Q

What proteins move towards the negative end of microtubules?

A

Dyneins.

76
Q

What is the basic structure of the motor proteins associated with microtubules?

A
  1. They both have two ATP binding heads and a tail
  2. Both have ATPase activity.
  3. Different cargo can be transported depending on what the kinesins and dyneins interact with.
77
Q

What drives the movement of motor proteins along microtubules?

A
  1. ATP hydrolysis.
  2. ATP hydrolysis provides the energy for conformation changes in the head that allows it to move along the microtubule in a cycle of binding release and rebinding.
78
Q

What drug interferes with polymerisation of microtubules and how?

A
  1. Nocodazole.

2. The golgi is pulled towards the centrosome and microtubules disassemble.

79
Q

What direction do microtubules face in axons?

A

The negative ends are orientated towards the cell body.

80
Q

What motor protein transport material to the termini in axons?

A

Kinesins.

81
Q

What motor protein transports material to the cell body in axons?

A

Dyneins.

82
Q

What happens to the centrosome before mitosis?

A
  1. The centrosome is located just outside the nucleus
  2. Just before mitosis the centrosome duplicates
  3. The two centrosomes move apart until they are at opposite sides of the nucleus (the nuclear envelope breaks down
83
Q

What happens to the centrosomes as mitosis proceeds?

A
  1. As mitosis proceeds, microtubules grow out from each centrosome with their plus ends growing towards the equatorial plate forming spindle fibres
  2. Duplicated chromosomes line up on spindle poles and are pulled apart
84
Q

What drugs interfere with microtubule assembly?

A

Colchicine and taxol.

85
Q

What do the drugs that interfere with microtubule assembly do?

A
  1. Colchicine binds free tubulin and prevents polymerisation into microtubules
  2. Taxol binds tightly to microtubules and prevents them from losing subunits
  3. Both are anti-mitotic
  4. Can be used to treat some cancers. Interfere with mitosis in rapidly dividing cells.
86
Q

What is the primary function of cilia?

A

Move fluid over a cell or a cell through a fluid.

87
Q

What is the difference between cilia and flagella?

A

They are similar in their internal structure, but flagella are usually much longer.

88
Q

Where do cilia and flagella grow out from?

A

Basal bodies.

89
Q

What is the cycle that cilia undergo?

A

Power stroke followed by recovery stroke.

90
Q

What allows cilia and flagella to bend?

A
  1. The bending of cilia and flagella is driven by Dynein walking along adjacent microtubule doublet.
  2. Adjacent doublets are held together by nexin.
  3. Because nexin links are stable, walking of the dynein along (towards minus end) neighbouring microtubule causes bending, rather than ‘sliding’ that would occur if the nexin was not present.
91
Q

How is organelle movement generated

A
  1. Co-ordinated movement of myosins attached to cellular organelles can move organelles along actin filaments
92
Q

What is difference between nucleation of actin filaments and microtubules

A
  1. Actin filaments often nucleated at PM

2. Microtubules nucleated from centre of cell

BB10005 COPY (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions