Cytoskeleton Pt 1

Question 1

Cytoskeleton is a

Answer 1

supportive network of fibers, filaments, and associated proteins.

is dynamic and adaptable

Question 2

Main functions of the cytoskeleton

Answer 2

Cell Shape: Neurons branch out, amoebas
Change shape when they move towards a food source

Strength: Mechanical strength (supportive), intermediate filaments support nuclear envelope

Cell movement: Organelles move around within cell while attached to cytoskeletal structures. Motor proteins can move vesicles along cytoskeletal filaments

Solid State Biochemistry: Metabolic pathways
anchored to cytoskeletal platform in liquid medium (increase reaction rates of enzymes, ex. glycolysis)

Question 3

Microtubules Overview

Answer 3

largest (25nm diameter), composed of tubulin protein (allows for follow rigid structure)

Support (allows vesicular transport, “tracks” in cell)
Position organelles
Framework/necessary for cell division/ mitotic spindle
Forms various structures ex. Cilia

Question 4

Intermediate filaments Overview

Answer 4

mid-sized (10nm diameter). Constructed from a number of different subunit proteins

Line up- creases rope like structure - mechanical strength.

Question 5

Actin filaments Overview

Answer 5

smallest (6 nm diameter), made up of actin protein.
Muscle contraction
Dynamics/ Rearrangements allow for cell movements - leading edge
Present under plasma membrane, plasma cortex

Question 6

Accessory proteins Overview

Answer 6

Regulate and link the filaments to other cell components, as well as to each other

ex. mussel contractions
filament polymerizing and depolymerizing

Question 7

Microtubules are composed of

Answer 7

tubulin subunits (hetero dimer)
alfa and beta subunits

monomers are synthesized and rapidly self associate to form dimers

Have structural polarity - two sides are different - different dynamics on either side

Question 8

Microtubule Protofilament formation

Answer 8

Heterodimers line up to form it
Beta tubulin - Plus end
Alfa tubulin - Minu end

Have head to tail arrangement - all point in same direction

Question 9

Alfa Tubulin

Answer 9

GTP bound CANNOT be hydrolyzed or exchanged (integral part of structure)

Question 10

Betta Tubulin

Answer 10

GTP or GDP bound, exchangeable/can be hydrolyzed (dynamic part of structure)

Question 11

Formation of microtubule from protofilament

Answer 11

13 protofilaments - to make microtubule
NON-covalent interactions

longitudinal contacts between dimers
also lateral contact - keeps structure together

middle of microtubule is harder to break because it ahs more interactions

Question 12

Nucleation of microtubule

Answer 12

slower phase - built from ring - grows from base

Makes the platform/template to build from

Question 13

elongation of microtubule

Answer 13

polymerization of microtubule

Question 14

Steady state of microtubule

Answer 14

also equilibrium - balance between tubulin addition and disassociation

length of microtubule does not change

Question 15

There is a Preferential growth of Microtubules at the ___ end

Answer 15

Plus end

Plus end favored for elongation

Minus end biased against elongation

Question 16

Microtubule dynamics are Influenced by

Answer 16

binding and hydrolysis of GTP (β tubulin allows for)

Question 17

Tubulin subunits at end of microtubule (T or D form) depends on

Answer 17

Rates of GTP hydrolysis and tubulin addition

Question 18

In microtubules, when the rate of subunit addition is high

Answer 18

(filament growing rapidly), likely new subunit will be added BEFORE nucleotide in previous subunit is hydrolyzed (tip remains in T form, forms a GTP cap)

Question 19

In microtubules, when the rate of subunit addition is low

Answer 19

hydrolysis may occur before next subunit is added, tip in D form

Question 20

Dynamic instability in microtubules is when

Answer 20

one end is growing and/or the other end is shrinking

Question 21

Microtubule catastrophe

Answer 21

Change from growth to shrinkage. Hydrolysis more rapid then subunit addition.

Question 22

Microtubule rescue

Answer 22

Change from shrinkage to growth, GTP subunits add to shrinking end, new GTP cap

Question 23

Microtubule T end promotes

Answer 23

polymerization

Question 24

Microtubule D end promotes

Answer 24

depolymerization

GTP hydrolysis changes subunit conformation and weakens binding affinity in the polymer

Question 25

How is a GTP cap formed

Answer 25

If the rate of subunit addition is high—and thus the filament is growing rapidly—then it is likely that a new subunit will be added to the end of the polymer before the GTP in the previously added subunit has been hydrolyzed.

In this case, the tip of the polymer remains in the T form, forming a GTP cap.

Question 26

Why do we need dynamic instability?

Answer 26

May reduce time required to find a target (formation of mitotic spindle, microtubules search for chromosomes).

Microtubules could explore the interior of the cell.

Question 27

How is a microtubule polar

Answer 27

The subunits point in the same direction (head to tail, alfa - betta +)

Question 28

What keeps tubulin together in the microtubule?

Answer 28

Non covalent interactions
longitudinal interactions (inc binding affinity between alfa and betta)
Latter associations (between profilamants, alfa-alfa, betta-betta)

Question 29

Difference between beta and alpha tubulin within the dimer?

Answer 29

Both bind to GTP
GTP B tubulin can be hydrolyzed
in Alfa tubulin - cannot be hydrolyzed, is part of dimer structure

Question 30

what does Taxol do

Answer 30

it binds to microtubule and stabilizes the polymerized from - preferentially killing dividing cells by not allowing cell division dynamics

( it is from dried bark of Pacific yew tree)

Question 31

What must happen at the end of the MT in order for it to stop shrinking and start growing?

Answer 31

(Rescue, change from shrinking to growing)
GTP cap needs to be established
GTP addition exceeds rate of hydrolysis

Question 32

How would an increase in GTP-tubulin concentration affect this switch from shrinking to growing?

Answer 32

Rate of addition of GTP tub grater at high tub concentrations

frequency of switching from shrinking to growing will increase with increases in tub concentration

Question 33

What would happen if GDP, but no GTP, is present in solution?

Answer 33

Continue to shrink and eventually disappear

GDP tub - binding affinity much lower

Question 34

Microtubule nucleation is the ____formation of microtubules

Answer 34

de novo

Question 35

Microtubules are nucleated from an
intracellular location called ___ which is enriched with ____

Answer 35

(MTOC):
Microtubule-organizing center
(enriched with γ tubulin)

Question 36

the γ tubulin small complex has

Answer 36

2 accessory proteins bind to two γ tubulin

Question 37

Formation of ___ , serves as template for microtubule nucleation

Answer 37

of spiral ring of γ tubulin molecules

(creates a microtubule with 13 protofilaments)

Question 38

spiral ring of γ tubulin associates with additional accessory proteins to form

Answer 38

γ tubulin ring complex: nucleate from minus end

Question 39

Centrosome is a

Answer 39

well defined MTOC in many animal cells, located near nucleus, from which MT are nucleated at their minus ends

Question 40

Centrioles are

Answer 40

Embedded within centrosome, cylindrical structure consists of MTs arranged in barrel shape

can nucleate (have gama tubulin)

Question 41

In Cells: The Minus-End of Microtubules are Linked to

Answer 41

MT-Organizing Centers (MTOC’s)

Question 42

The plus end of microtubules in interphase vs Mitosis

Answer 42

Interphase - Post to edge
Mitosis - duplicate and Post migrate to edge of cell

Question 43

Intermediate Filaments are found in ___

Regulated by ___

Provide____

Answer 43

Found in vertebrates, nematodes, mollusks (not in every eucaryotic cell)

Often regulated by phosphorylation/ dephosphorylation events

Prominent in cytoplasm of cells, subjected to mechanical stress: provide mechanical strength for squishy animals

Question 44

Examples of Intermediate Filaments

Answer 44

Nuclear Lamins - support the nuclear envelope

Keratins - Skin/ Hair

Question 45

Structure of Intermediate Filament

Answer 45

subunits of elongated proteins - coil together making coiled coil dimer (are amphipathic, hydrophobic interactions)

Coiled-coil dimer - The two ends are the same (do NOT have structural polarity)

Two coiled coil dimers make a staggered tetramer - arranged in opposite orientations

8 tetramers pack laterally to form filament

Large number of polypeptides lined up together, with strong lateral hydrophobic interactions (coiled coils), gives a ropelike character

Easily bent, difficult to break.

Question 46

Nuclear Lamins make up a

Answer 46

meshwork lining the inner membrane of the nuclear envelope

Question 47

Progeria results from

Answer 47

Point Mutation in the Lamin A gene (codes for the lamin protein intermediate filament)

Question 48

Progeria causes

Answer 48

a Fragile nuclear membrane, low tolerance to mechanical stress

Accelerated Aging

Question 49

Progeria signs include

Answer 49

growth failure,
loss of body fat and hair,
aged-looking skin,
stiffness of joints,
hip dislocation,
generalized atherosclerosis,
cardiovascular (heart) disease
and stroke

is fatal

Question 50

Keratins provide

Answer 50

Mechanical strength to epithelial tissue by anchoring the intermediate filaments at sites of cell-cell contact (desmosomes) or cell-matrix contact (Basal side, Basal lamina) (hemidesmosomes)

Tough coverings for animals, skin, hair, nails, claws, and scales

Question 51

Defective Keratins in basal cell layer of epidermis causes ___

Answer 51

Epidermolysis bullosa simplex

Skin blisters in response to very slight mechanical stress, which ruptures basal cells

Question 52

Epidermolysis bullosa simplex treatment

Answer 52

lost of gauze and wrappings to prevent friction