Ch. 17 Cytoskeleton, Intermediate Filaments, Microtubules

Question 1

list the functions of the cytoskeleton

Answer 1

• strength
• structure
• organization
• movement
• participates in cellular division

Question 2

describe the cytoskeleton

Answer 2

internal network of proteins that helps to organize the cell and its organelles

Question 3

is the cytoskeleton rigid/fixed in place. briefly explain

Answer 3

• no!
• dynamic in nature
• rapidly-changing
• it is integral for cells to have movement to be able to interact with their environments, therefore it would not make sense for the cytoskeleton to be fixed in place

Question 4

how are organelles able to move around the cell due to the cytoskeleton

Answer 4

“tracks” are laid which allow for the movement

Question 5

how does the cytoskeleton help with cellular division

Answer 5

• able to move chromosomes around the cell **

Question 6

what are the types of protein filaments making the cytoskeleton

Answer 6

• intermediate filaments
• microtubules
• actin filaments

Question 7

what is an alternative name for actin filaments

Answer 7

microfilaments (actin = thin filament)

Question 8

list the protein filaments from highest to lowest size

Answer 8

microtubules, intermediate filaments, micro/actin-filaments

Question 9

describe the general role of intermediate filaments

Answer 9

strengthens the cells against mechanical force (esp pressure on skin)

Question 10

define a desmosome

Answer 10

structural connection between intermediate filaments in adjacent cells

Question 11

what would happen to the skin if it did not have intermediate filaments

Answer 11

any type of stretch would rupture the cells

Question 12

compare sheets of cells with and without intermediate filaments through a drawing to show how stretching affects each case

Answer 12

….

Question 13

the top outside layer of the skin is able to withstand a lot of stimulation, stretching, pressure, and manipulation whilst still remaining intact. what is the top layer of the skin therefore referred to and how is this “resistance” possible

Answer 13

• (dead) keratinocytes
• keratin fibres (a type of IF) are able to remain there through connection by desmosomes

Question 14

for most people, the skin is the last organ that people think to take care of, especially due to its “resistance” to manipulation. some people unfortunately are faced with problems with their skin that oppose this, such as epidermolysis bullosa simplex. those facing this condition suffer from large, painful blisters with even the slightest bit of heat or friction. why do you think that this condition happens?

Answer 14

• genetic mutation of the intermediate filaments prevents their correct formation
• this makes the skin extremely fragile in which the cells lyse even with gentle pressure

Question 15

what is the main type of role for the intermediate filaments, why?

Answer 15

• structure/strength providing
• greater stability than microtubules and microfilaments

Question 16

describe the appearance of an intermediate filament

Answer 16

ropelike (8 long tetramers), filaments twining to make one larger structure, 10nm in diameter

Question 17

describe the structure of a monomer

Answer 17

alpha helical region in between amine and carboxylic acid groups at opposing ends

Question 18

describe the structure of a dimer

Answer 18

two alpha-helices coiled around one another, with two amines and two carboxylic acids at opposing ends

Question 19

describe the structure of a tetramer

Answer 19

• two coils coiled around one another
• two amines from a dimer and two COOH groups from the other dimer will be one end on both sides (opposing polarities)
• staggered

Question 20

what is the importance of tetramers being staggered dimers

Answer 20

improves their strength

Question 21

what bonds are involved in dimers and tetramers

Answer 21

non-covalent bonding

Question 22

what are the types of intermediate filaments

Question 23

what remains relatively constant in all types of intermediate filaments and what does this help with

Answer 23

• alpha-helix region (size and amino acid sequence)
• allows for different types of monomers to bind with one another and make composite intermediate filaments

Question 24

what varies between the intermediate filaments and what does this cause for the functions

Answer 24

• globular head and tail regions
• allows for different functions in different cell types

Question 25

what are the main categories of intermediate filaments

Answer 25

cytoplasmic and nuclear

Question 26

what are the types of intermediate filaments, and what category are they part of

Answer 26

- keratins, vimentin/vimentin-related, neurofilaments (cytoplasmic) - nuclear lamins (nuclear)

Question 27

where are keratin IFs predominantly present

Answer 27

epithelia (sheet tissues)

Question 28

where are vimentin/vimentin-related IFs present

Answer 28

connective tissue, muscle cells, neuroglial/neural support cells

Question 29

where are neurofilament IFs predominantly present

Answer 29

nerve cells

Question 30

where are nuclear lamin IFs present

Answer 30

all animal cells (they line inside of nuclear membrane)

Question 31

what are laminins

Answer 31

proteins found on extracellular matrix** db check

Question 32

what type of support does the nuclear envelope receive

Answer 32

meshwork of nuclear lamins

Question 33

aside from their relative location, what is the main difference between cytoplasmic IFs and nuclear IFs

Answer 33

cytoplasmic IFs are ropelike (random pattern) whereas nuclear IFs have a meshwork structure (organized)

Question 34

describe the meshwork structure of nuclear IFs

Answer 34

- 2D - on inner nuclear membrane - strong (able to dissemble and reassemble during each cell division thru (de)phosphorylation of lamins)

Question 35

describe progeria

Answer 35

- rare genetic disorders due to mutation of the lamins (collective term is progeria) - extremely fast aging starting within first 2 years of life - not fully understood - causes nuclear instability

Question 36

what may nuclear instability cause

Answer 36

interference with body's ability of cellular division and repair

Question 37

what is the main role of microtubules

Answer 37

organization for cell interior

Question 38

describe microtubules

Answer 38

- thickest cytoskeletal fibres - ability to move organelles, chromosomes, molecules around (motility) - present in cytoplasm of all eukaryotic cells (including cilia and flagella when present) - dynamic instability

Question 39

what types of roles does the microtubule have

Answer 39

structural (some) and organizational (main)

Question 40

draw out how microtubules are able to transport cargo along a nerve cell (indicate the "polarity" of the microtubules)

Answer 40

main points: all microtubules are oriented in the same direction based on the polarity which allows for directional protein transport

Question 41

for cargo transport along nerve cells, we can consider ________ as the tracks and ___________ as the engines

Answer 41

microtubules; motor proteins

Question 42

in reference to microtubule polarity what direction is inward transport, outward transport?

Answer 42

- negative end of MT (toward end of cell body) - positive end of MT (toward axon terminal)

Question 43

describe tubulin structure

Answer 43

dimer of alpha and beta tubulin subunits

Question 44

describe the structure of microtubules

Answer 44

- hollow tubes of tubulin - made of 13 protofilaments - 20-25nm

Question 45

what is a protofilament

Answer 45

ordered row of tubulin dimers

Question 46

what is a tubulin heterodimer

Answer 46

microtubule subunit (one alpha and one beta subunit)

Question 47

draw out tubulin heterodimer, protofilament, and microtubules

Answer 47

....

Question 48

what subunit of microtubules is associated with plus ends

Answer 48

beta

Question 49

what subunit of microtubules is associated with minus ends

Answer 49

alpha

Question 50

what is the major organizing center in animal cells

Answer 50

centrosome

Question 51

describe centrosomes

Answer 51

- membrane-free organelle that organizes microtubules - close to nucleus - have gamma tubulin ring complexes

Question 52

most microtubules emanate from what region of the cell

Answer 52

nucleus

Question 53

what is the purpose of the gamma tubulin ring complexes in the centrosome

Answer 53

to act as nucleation sites for polar microtubule growth initiation from centrosome region

Question 54

which charge end of the microtubules is closest to the centrosome; furthest?

Answer 54

negative; positive

Question 55

what does it mean when we say that microtubules are dynamically unstable

Answer 55

they are constantly growing and shrinking (in a rapid and independent manner)

Question 56

what does it mean when we say that microtubules are growing and shrinking independently on the same centrosome

Answer 56

not all microtubules will shrink at the same time nor will they all grow at the same time (asynchronous)

Question 57

how is dynamic instability of microtubules foundationally possible

Answer 57

ability of tubulin molecules to hydrolyze GTP

Question 58

what is a GTP-cap

Answer 58

packed GTP-bound dimers on a growing microtubule, which help to stabilize it

Question 59

disassembly (i.e. shrinkage) of a microtubule is favoured by which bound tubulin dimer

Answer 59

GDP

Question 60

stable microtubules (growing) are able to express capping proteins on themselves. they can be further stabilized by attaching to

Answer 60

proteins in the cell thru "plus" ends

Question 61

why are microtubules in mature neurons stable

Answer 61

they have caps which can allow for permanent transport route