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Cell Bio Final Exam > Cytoskeleton Pt 1 > Flashcards

Cytoskeleton Pt 1 Flashcards

1
Q

Cytoskeleton is a

A

supportive network of fibers, filaments, and associated proteins.

is dynamic and adaptable

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2
Q

Main functions of the cytoskeleton

A

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)

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3
Q

Microtubules Overview

A

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

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4
Q

Intermediate filaments Overview

A

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

Line up- creases rope like structure - mechanical strength.

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5
Q

Actin filaments Overview

A

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

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6
Q

Accessory proteins Overview

A

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

ex. mussel contractions
filament polymerizing and depolymerizing

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7
Q

Microtubules are composed of

A

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

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8
Q

Microtubule Protofilament formation

A

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

Have head to tail arrangement - all point in same direction

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9
Q

Alfa Tubulin

A

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

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10
Q

Betta Tubulin

A

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

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11
Q

Formation of microtubule from protofilament

A

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

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12
Q

Nucleation of microtubule

A

slower phase - built from ring - grows from base

Makes the platform/template to build from

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13
Q

elongation of microtubule

A

polymerization of microtubule

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14
Q

Steady state of microtubule

A

also equilibrium - balance between tubulin addition and disassociation

length of microtubule does not change

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15
Q

There is a Preferential growth of Microtubules at the ___ end

A

Plus end

Plus end favored for elongation

Minus end biased against elongation

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16
Q

Microtubule dynamics are Influenced by

A

binding and hydrolysis of GTP (β tubulin allows for)

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17
Q

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

A

Rates of GTP hydrolysis and tubulin addition

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18
Q

In microtubules, when the rate of subunit addition is high

A

(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)

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19
Q

In microtubules, when the rate of subunit addition is low

A

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

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20
Q

Dynamic instability in microtubules is when

A

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

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21
Q

Microtubule catastrophe

A

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

22
Q

Microtubule rescue

A

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

23
Q

Microtubule T end promotes

A

polymerization

24
Q

Microtubule D end promotes

A

depolymerization

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

25
How is a GTP cap formed
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.
26
Why do we need dynamic instability?
May reduce time required to find a target (formation of mitotic spindle, microtubules search for chromosomes). Microtubules could explore the interior of the cell.
27
How is a microtubule polar
The subunits point in the same direction (head to tail, alfa - betta +)
28
What keeps tubulin together in the microtubule?
Non covalent interactions longitudinal interactions (inc binding affinity between alfa and betta) Latter associations (between profilamants, alfa-alfa, betta-betta)
29
Difference between beta and alpha tubulin within the dimer?
Both bind to GTP GTP B tubulin can be hydrolyzed in Alfa tubulin - cannot be hydrolyzed, is part of dimer structure
30
what does Taxol do
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)
31
What must happen at the end of the MT in order for it to stop shrinking and start growing?
(Rescue, change from shrinking to growing) GTP cap needs to be established GTP addition exceeds rate of hydrolysis
32
How would an increase in GTP-tubulin concentration affect this switch from shrinking to growing?
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
33
What would happen if GDP, but no GTP, is present in solution?
Continue to shrink and eventually disappear GDP tub - binding affinity much lower
34
Microtubule nucleation is the ____formation of microtubules
de novo
35
Microtubules are nucleated from an intracellular location called ___ which is enriched with ____
(MTOC): Microtubule-organizing center (enriched with γ tubulin)
36
the γ tubulin small complex has
2 accessory proteins bind to two γ tubulin
37
Formation of ___ , serves as template for microtubule nucleation
of spiral ring of γ tubulin molecules (creates a microtubule with 13 protofilaments)
38
spiral ring of γ tubulin associates with additional accessory proteins to form
γ tubulin ring complex: nucleate from minus end
39
Centrosome is a
well defined MTOC in many animal cells, located near nucleus, from which MT are nucleated at their minus ends
40
Centrioles are
Embedded within centrosome, cylindrical structure consists of MTs arranged in barrel shape can nucleate (have gama tubulin)
41
In Cells: The Minus-End of Microtubules are Linked to
MT-Organizing Centers (MTOC’s)
42
The plus end of microtubules in interphase vs Mitosis
Interphase - Post to edge Mitosis - duplicate and Post migrate to edge of cell
43
Intermediate Filaments are found in ___ Regulated by ___ Provide____
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
44
Examples of Intermediate Filaments
Nuclear Lamins - support the nuclear envelope Keratins - Skin/ Hair
45
Structure of Intermediate Filament
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.
46
Nuclear Lamins make up a
meshwork lining the inner membrane of the nuclear envelope
47
Progeria results from
Point Mutation in the Lamin A gene (codes for the lamin protein intermediate filament)
48
Progeria causes
a Fragile nuclear membrane, low tolerance to mechanical stress Accelerated Aging
49
Progeria signs include
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
50
Keratins provide
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
51
Defective Keratins in basal cell layer of epidermis causes ___
Epidermolysis bullosa simplex Skin blisters in response to very slight mechanical stress, which ruptures basal cells
52
Epidermolysis bullosa simplex treatment
lost of gauze and wrappings to prevent friction

Cell Bio Final Exam (5 decks)

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