Cytoskeleton & Cell Adhesion

Question 1

How thick are microfilaments?

Answer 1

7nm

Question 2

How thick are intermediate filaments?

Answer 2

10nm

Question 3

What is the diameter of a microtubule?

Answer 3

25nm

Question 4

What can microfilaments also be called? (2)

Answer 4

Actin filaments

F-actin

Question 5

What are the subunits of microfilaments?

Answer 5

G-actin

Question 6

What percentage of the total protein of the cell is comprised of microfilaments?

Answer 6

5%

Question 7

How many subunits per complete turn of the microfilaments helix?

Answer 7

13 G-actin

Question 8

What is the structure of a microfilament?

Answer 8

Polarised double helix

Question 9

How long is one complete turn of the microfilament helix?

Answer 9

37nm

Question 10

Why do microfilaments display polarity?

Answer 10

G-actin monomers are asymmetrical

Question 11

What molecule is required for the growth of microfilaments?

Answer 11

ATP

Question 12

On what end does microfilament growth/shortening occur fastest?

Answer 12

Plus end

Question 13

What are the major functions of microfilaments? (3)

Answer 13

Mechanical support

Cell shape changes and maintenance

Cell motility

Question 14

What do actin-sequestering proteins do?

Answer 14

Bind to G-actin to prevent polymerisation

Question 15

What do capping proteins do?

Answer 15

Bind to ends of actin filaments to prevent growth (stabilisation)

Question 16

What do motor proteins do?

Answer 16

Allow movement

Question 17

What do cross-linking proteins do?

Answer 17

Hold actin cell cortex together

Question 18

What kind of intermediate filaments are found in epithelia?

Answer 18

Keratin

Question 19

What kind of intermediate filaments are found in neurons?

Answer 19

Neurofilamin/neurofilaments

Question 20

What kind of intermediate filaments are found in nuclei?

Answer 20

Lamins

Question 21

Where is the intermediate filaments network most dense usually?

Answer 21

Around the nucleus

Question 22

What are the functions of intermediate filaments? (3)

Answer 22

Provide rigidity

Anchor cells at some junctions

Support nuclear structure (and protect/attach chromatin)

Question 23

Describe the formation of intermediate filaments

Answer 23

One intermediate filament protein monomer = 2 intermediate filaments joined end-to-end

Two monomers come together to create a helical dimer

Two dimers combine = tetramer (fundamental unit)

Tetramers linked end-to-end in staggered formation

Question 24

What are the subunits of microtubules?

Answer 24

One alpha-tubulin and one beta-tubulin

Question 25

Which part of the microtubule subunit is positive?

Answer 25

Beta-tubulin

Question 26

How many subunits in a cross-section of a microtubule?

Answer 26

13

Question 27

What molecule is required for microtubule growth?

Answer 27

GTP

Question 28

At what end do changes in microtubule length occur fastest?

Answer 28

Plus end

Question 29

What organelles do microtubules usually grow out of and in what orientation?

Answer 29

Centrioles Minus end close to centrosome with plus end pointing to cell periphery

Question 30

What filament supports microvilli and stereocilia?

Answer 30

Microfilaments

Question 31

What are the functions of actin sheets in cells? (2)

Answer 31

Support in cell cortex Maintains cell shape

Question 32

What parts of the cytoskeleton are present in axons?

Answer 32

Intermediate filaments Microtubules (stabilise area close to synapse)

Question 33

What stabilises the processes of thrombocytes?

Answer 33

Microtubules

Question 34

What do microfilaments anchor?

Answer 34

Synaptic vesicles (close to presynaptic membrane)

Question 35

What organelle is organised by microtubules?

Answer 35

Endoplasmic reticulum

Question 36

Describe how cells move using actin.

Answer 36

1. Cell pushed out protrusions in front (leading edge) via actin polymerisation 2. Protrusions adhere to surface using focal adhesions (containing integrins) 3. F-actin connects to focal adhesions 4. Rest of cell pulls against anchorage points and drags itself forward 5. Actin depolymerises at rear

Question 37

What are the two types of protrusions caused by actin polymerisation?

Answer 37

Lamellipodia (thick) Filopodia (thin)

Question 38

What motor protein pulls on F-actin to drag the cell forward?

Answer 38

Myosin II (non-muscle)

Question 39

What cell structure is stabilised by microtubules?

Answer 39

Cilia

Question 40

What MAP causes cilia movement and how do cilia move?

Answer 40

Dynein Spiral movement

Question 41

What is used to transport synaptic vesicles along axons?

Answer 41

Microtubules Kinesin (to plus end) Dynein (to minus end)

Question 42

What part of the cytoskeleton do chemotherapeutic agents target and why?

Answer 42

Microtubules Involved in movement of chromosomes/mitotic spindle

Question 43

How do colchicine and vinblastine work?

Answer 43

Destabilise microtubules (cut up)

Question 44

How does taxol work?

Answer 44

Stabilises microtubules (cannot change length to move chromosomes)

Question 45

What is caused by a mutation in the dystrophin gene?

Answer 45

Duchenne and Becker muscular dystrophy (actin)

Question 46

What is caused by a mutation in the myosin VII gene?

Answer 46

Usher’s syndrome (hereditary blindness and deafness) - actin/disrupts stereocilia

Question 47

What is caused by keratin gene mutations?

Answer 47

Epidermolysis bullosa symplex (skin highly sensitive to mechanical injury; blistering) - Intermediate filaments

Question 48

What is caused by plectin mutations?

Answer 48

Epidermolysis bullosa symplex with muscular dystrophy

Question 49

What causes Alzheimer’s disease?

Answer 49

Hyperphosphorylated Tau (MAP) builds up and cannot bind - microtubules

Question 50

What is caused by a mutation in the spastin gene?

Answer 50

Hereditary Spastic Paraplegia - microtubules (microtubule severing protein)

Question 51

How does Listeria bacteria hijack actin filaments?

Answer 51

1. Listeria engulfed by host 2. Bacterium escapes from phagocytic vesicle and divides 3. F-actin polymerised at back of bacterium to give it motility 4. Actin ‘comet’ drives bacterium into neighbouring cell

Question 52

How does the vaccinia virus use host cells?

Answer 52

1. Virus engulfed by host 2. Virus escapes phagocytic vesicle and divides 3. Uses microtubules to be transported to cell periphery 4. F-actin polymerised at back of virus 5. F-actin comet drives virus into neighbouring cell