Cytoskeleton

Question 1

cytoskeleton determines

Answer 1

• organization

- polarity

Question 2

a cell has to:

Answer 2

• be correctly shaped
• be physically robust
• be internally structured
• change its place and move from place to place

Question 3

3 different types of filaments that compose the cytoskeleton

Answer 3

1. Actin filaments
2. Intermediate filaments
3. Microtubules

Question 4

Actin filaments

Answer 4

• determine shape of cell

- necessary for cell locomotion

Question 5

Microtubules

Answer 5

• determine positions of membrane-bound organelles
• direct intracellular transport
• form mitotic spindle

Question 6

Intermediate filaments

Answer 6

• provide mechanical strength

Question 7

tubulin

Answer 7

• protein polymers that makeup MT

- subunit that is a heterodimer (alpha and beta)

Question 8

alpha-tubulin

Answer 8

• has a binding site that holds GTP

- GTP that is bound is never hydrolyzed or exchanged

Question 9

beta-tubulin

Answer 9

• has a binding site that can hold either GTP or GDP

- exchangable

Question 10

MT characteristics

Answer 10

• hollow cylindrical structures made out of protofilaments

Question 11

protofilaments

Answer 11

• composed of alpha-beta tubular heterodimers

Question 12

How do microtubules grow and shrink?

Answer 12

process: dynamic instability

Question 13

dynamic instability

Answer 13

• binding and hydrolysis of GTP that occurs only in the beta subunit of tubular dimer
• addition of GTP-containing tubular to end of protofilament -> growth

Question 14

Microtubules originate from a specific cellular location

Answer 14

microtubule organizing center (MTOC)

- e.g. in animal cells -> centrosome is major MTOC

Question 15

MT function during cell division

Answer 15

when cell divides, MT rearrange to form a bipolar mitotic spindle
- this is responsible for aligning and segregating the chromosomes

Question 16

Microtubule-associated proteins (MAPs)

Answer 16

• move along MT bringing transport vesicles to target organelles in the cell
• can move organelles and vesicles in the cell
• can move vesicles with pigments in the skin

Question 17

kinensin

Answer 17

travels toward plus end

Question 18

dynein

Answer 18

travels toward minus end

Question 19

melanosomes

Answer 19

pigments

Question 20

flagella

Answer 20

used to move cells in a liquid environment

- e.g. spermatozoids

Question 21

cilia

Answer 21

move fluid above a cell

- e.g. mucus in respiratory epithelium

Question 22

MT- Specific Drugs

Answer 22

• Taxol: binds & stabilizes MTs

- Colchicine, colcemid, vinblastine, vincristine, nocodazole: binds subunits and prevents their polymerization

Question 23

Taxol (Paclitaxel)

Answer 23

• anticancer chemotherapy
• blocking Mts to kill cancer cells
• blocks depolimerization

Question 24

Colchicin

Answer 24

• alkaloid of the autumn crocusses
• binds free tubular -> prevents MT polymerization and cell division
• anti-inflammatory effects

Question 25

Vinca alkaloids

Answer 25

- binds free tubulin -> prevents MT polymerization and cell division

Question 26

Actin

Answer 26

- form a tight, right-handed helix called filamentous actin (F-actin) - consists of 2 parallel protofilaments - helix - flexible structure

Question 27

Actin filament

Answer 27

- polymerize to grow - depolymerize - ATP bound actin has higher affinity for neighboring subunit and remains stable in the filament - ADP bound actin can more easily dissociate from filament

Question 28

Actin crosslink

Answer 28

villin, fimbrin

Question 29

Stress fiber

Answer 29

contractile bundle

Question 30

Cell Cortex

Answer 30

gel-like network

Question 31

Filopodium

Answer 31

tight-parallel bundle

Question 32

Actin-associated proteins & muscle contraction

Answer 32

- kinesin - myosin - dynein

Question 33

tropomyosin

Answer 33

- blocks myosin-binding site

Question 34

myosin-binding site

Answer 34

- exposed by Ca2+-mediated tropomyosin movement | - a lot of Ca2+ present in sarcomere

Question 35

ATP + Ca2+

Answer 35

- needed to walk along actin filament (movement)

Question 36

Phalloidin

Answer 36

- toxin of the death cap - toxic esp. to liver cells - binds actin filaments & blocks depolimerisation - stabilization - cell not able to move or maintain homeostasis - alpha-amanitin inhibits RNA-Polymerase II - main toxicity of the death cap

Question 37

Intermediate filaments

Answer 37

- no polarity (+/-) - subunits don't contain ATP or GTP - don't play a role in cell movement - no motor proteins associated - BUT, associated with: - cell-cell junctions - strengthening cells and epithelia - giving tissues mechanical stability - mechanical resistance: prevents separation of skin

Question 38

monomer

Answer 38

one protein

Question 39

in final intermediate filament

Answer 39

- there are 16 dimers of IF monomers = 32 coiled coils - very strong structure - network of noodles in cell

Question 40

keratin filaments

Answer 40

- intermediate filament - produced by keratinocytes in the epidermis - made up of keratin (subunit) - formation of horns, nails, hair - anchoring of epithelial cells via desmosomes/hemidesmosomes

Question 41

cytoskeleton components of MICROFILAMENTS

Answer 41

- 2 helical crossed ACTIN strands - thinnest diameter - subunit: ACTIN - functions: - maintains cells shape - changes cells shape - muscle contraction - cell movement - in periphery of cell, sometimes running parallel

Question 42

cytoskeleton components of MICROTUBULES

Answer 42

- tubes of strands per MT - thickest in diameter (has a lumen) - subunit: alpha and beta-tubulin - functions: - maintains cell shape - cell movement - chromosome movement during cell division - movement of organelles - comes from organizing center (centrosomes) and spreading towards cell periphery

Question 43

cytoskeleton components of INTERMEDIATE FILAMENTS

Answer 43

- long molecules polymers - subunit: keratin, lain, vimentin (all proteins) - functions: - maintains cell shape - mechanical shape - formation of nuclear lamina - distributed along whole cytoplasm of cell, building NETWORK of filaments in cytosol