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PHGY 170 > Module 5 > Flashcards

Module 5 Flashcards

1
Q

what is the cytoskseleton

A

network of structural proteins found in all cell types, defines cell shape and distribution of cellular content

occupies a large portion of the cytosol

permits signalling, vesicular transport and can allow cell motility

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2
Q

what are the classes of structural proteins

A
  • intermediate filaments
  • microtubules
  • actin
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3
Q

what are intermediate filaments

A

supply mechanical strength to cells allowing them to resist changes of shape (strongest filament)

are polymers and their expression is tissue and cell specific

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4
Q

primary structure of intermediate filaments

A

polymer of amino acids link together by peptide bonds

at this stage filaments have the same strength as other proteins in the body

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5
Q

secondary structure of intermediate filaments

A

rich in alpha helices
- responsible for long, coiled structure of filaments
- hydrogen bonds stabilize structure (resist stretching and prevent collapse)

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6
Q

tertiary and quaternary structure of intermediate filaments

A

tertiary - coiled monomer

two coiled monomers come together to form a dimer
- monomers wrap around each other forming coiled coil (allows max hydrogen bonding between peptides) giving great strength

two dimers assemble in antiparallel staggered manner forming tetramer
- increase hydrogen bonding and strength

tetramer building block of filament

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7
Q

assembly of intermediate filaments

A

8 tetramers come together to form a unit length filament (20nm)

unit length filaments come together to form a immature filament (interact loosely end to end)

immature filaments compact to form a mature filament (10nm)

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8
Q

intermediate filaments post translational modifications

A

help control shape and function

modifcations occur in the head and tail domains of the filament subunit proteins

phosphorylation leads to dissolution of the filament into unit length filaments, when phosphates removed by phosphatases filaments reform (process important for cell division)

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9
Q

what is lamin (intermediate filament)

A

found solely in nucleus

forms nuclear matrix

dense network to protect chromatin

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10
Q

what is desmin (intermediate filament)

A

does not form long thin filamentous structure

connects different cellular structures together

important for muscle structure integrity

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11
Q

what is keratin (intermediate filament)

A

binds to desmosomes to form a complex

makes up hair skin and nails

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12
Q

purpose of microtubules

A

cellular trafficking

movement of proteins, vesicles and some cellular organelles

create specific routes for cargo, can be assembled/dissembles to create or remove routes

travel can be bi direction and cargo can attach or detach anywhere along length

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13
Q

where does microtubules assembly occur

A

does not occur spontaneously

assembly required many proteins

occurs in regions called microtubule organizing centres (MTOCs)

assembled in different locations

example of an MTCO is the centrosome (used in cell division)

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14
Q

protein structure of microtubules

A

made up of tubulins (protein)

alpha and beta tubuline both globular protein with similar shapes that can bind tightly together (head to tail) to form a dimer

both tubulin proteins bind to a GTP molecules

beta tubulin can cleave its GTP to GDP, when bound to GDP beta has a shape change

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15
Q

microtubule polymerization/formation of the tubes

A

dimers spontaneously assemble into unstable polymers that can quickly fall apart

polymer of 6+ dimers is stable, may grow laterally or longitudinally (protofilament)

protofilaments form sheet and will assemble into a tube of 13 protofilaments

nucleation site for microtubule elongation

at the end of microtubule dimers come and go

rate of assemble greater grows, disassemble greater shortens

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16
Q

microtubule assembly

A

alpha tubulin always has GTP

beta may have GTP or GDP

when GTP bound to beta, dimer polymerization is favoured and dimers attach to each other

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17
Q

microtubule disassembly

A

when beta tubulins GTP is hydrolysed to GDP, dimer undergoes conformational change that promotes depolymerization

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18
Q

polarity of microtubule

A

ends are different, one plus one minus so polar

preference for dimer binding is at plus end so rate is faster there

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19
Q

microtubule dynamic instability

A

ability to rapidly grow or shrink which is necessary for responses to changes in cellular environment

growing microtubule has a cap of GTP subunits as tip

GTP hydrolysis occasionally exposes GDP bound subunits at tip

rapid catastrophic depolymerization occurs

GTP subunits bind to recap microtubule and stop depolymerization

growth reoccurs when GTP bound dimers available until another change in environment is detected

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20
Q

microtubule catastrophe measures against

A

when there is rapid depolymerization resulting in shortening

capping
plus ends capping proteins bind adding stability, keep them polymerized even if GDP bound form

rescue
halted or revered, occurs spontaneously is enough GTP dimers present. can occurs in the presence of some other proteins

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21
Q

functions of microtubule based motor proteins

A

control trafficking

bind to cargo thats needs to be moved then binds to microtubule and walks along it

process consumes ATP

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22
Q

types of microtubule motor proteins

A

kinesin
moves towards plus end

dynein
moves towards minus end

heads contain microtubule binding domains, have two heads

tails bind to cargo

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23
Q

walking of motor proteins process

A

head 1 bound to microtubule, head 2 bound to ADP

walking initiated by ATP binding to head 1, conformational change > head 2 swings around

head 2 goes overing binding site on microtubule and binds releasing ADP

head 1 undergoes hydrolysis so ADP bound, release from microtubule

process repeats

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24
Q

actin and microtubules similarities

A

composition
- globular proteins

movement
- motor proteins used to initiate movement along both proteins

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25
Q

actin and microtubule differences

A

network formation
- microtubules form dynamic network
- actin forms stronger network that contributes to both structure of the cell and large scale movements (muscle contraction)

actin cytoskeleton can move the cell itself

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26
Q

basic building block of actin

A

actin monomers

cells can express several different types of actin monomers which allow the cells to match the monomers to their specific functional needs

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27
Q

formation of actin filmaments

A

actin monomers come together to form long thin actin filaments

bind longitudinally and laterally (high tensile strength can withstand pulling forces that would pull microtubules apart)

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28
Q

actin filaments polarization

A

there is a plus end (barbed end), and minus end (pointed end)

29
Q

actin polymerization (what it binds to)

A

actin monomers bind to nucleotide phosphates (ATP/ADP)

binding of ATP promotes assembly

ADP disassembly

preference for ATP so when there is a constant source ADP is replaced

30
Q

stages of actin polymerization/formation of filament

A

nucleation
- two actin monomers dimerize
- nucleation occurs when a third actin monomer binds to the dimer to form a nucleus trimer
- trimer forms core

elongation
- actin monomers added to core, elongates in both directions (plus end favoured)
- dynamic process

steady state
- rate of assembly equals disassembly so net elongation ceases

31
Q

actin treadmilling

A

treadmilling is the favoured addition of monomers to one end and the same rate of removal on the other end

keeps filament same length but moves is within the cell

allows cell to rapidly adjust actin cytoskeleton much faster than intermediate filaments which require phosphorylation

32
Q

when does actin treadmilling occur

A

regulated by ATP actin concentration compared to ADP bound actin

ATP lower at plus end than minus end

if ATP concentration increases above critical concentration for the minus end, monomers can be added again

33
Q

acting binding proteins types

A
  • monomer binding proteins
  • nucleating proteins
  • capping proteins
  • severing and depolymerization proteins
  • cross linking proteins
  • membrane anchors
  • actin binding motor proteins
34
Q

monomer binding proteins

A

directly bind to actin monomers to influence polymerization

35
Q

nucleating proteins

A

bind to actin polymers to increase stability and allow growth of a new branch

36
Q

capping protein

A

bind to plus or minus end to stabilize polymer and prevent assembly/disassembly

37
Q

severing and depolymerization proteins

A

bind to actin polymer and sever or induce disassembly

38
Q

cross linking protein

A

allow side to side linkage of actin polymers to form bundles of actin filaments

39
Q

membrane anchors

A

link actin filaments to non actin structural proteins (intergrins)

40
Q

actin binding motor proteins

A

bind to actin filament and allow movement

myosin (has 18 different families, each perform specific roles)

41
Q

myosin structure

A

motor domain, formed by heavy chain, binds to actin filament and ATP

regulatory domain formed by heavy chain, moves back and forth as myosin moves

tail domain binds to other cellular proteins or myosin

42
Q

movement of myosin

A

hydrolysis
- ATP bound to motor domain, myosin is unbound to filament
- hydrolysis of ATP to ADP and inorganic phosphate cause conformational shift in regulatory domain (swing like a lever)

actin binds
- motor domain binds to actin filament
- inorganic phosphate released
- conformational change and pulling myosin along filament
- ADP released, ATP rebind cause myosin to unbind from actin

movement
- myosin moved towards plus end (barbed)

43
Q

cellular migration

A

physical movement of a cell

needs lots of coordination to ensure contents stay intact and functional

dynamic assembly/disassembly of cytoskeleton filaments important to generate forces and coordination for migration

44
Q

process of cellular migration

A

initiated when actin filaments polymerize near the plasma membrane and push it outwards

pushing forces dont rip the membrane due to hydrophobic interactions between membrane phospholipids

as filopodia and lamellipodia extend plasma membrane bound integrins bind to extracellular matrix

filaments bind to integrins as anchors

45
Q

types of migration actin filaments

A
  • filopodia
  • lamellipodia
  • stress fibers
45
Q

filopodia

A

thin parallel bundles of filaments

plus end facing membrane

extends in the direction of movement

46
Q

lamellipodia

A

larger sheet like bundles of actin filaments

plus end towards membrane

from broader structure that distend a wider amount of plasma membrane in the same direction as filopodia

47
Q

stress fibers

A

form around integrins

resemble flipodia but polarity different

grow towards the cytosol

rich in motor proteins and are anchored to the integrins allowing filaments to move forward

at trailing edge of cell integrins internalized and recycles and stress filaments are disassembles

48
Q

cell cycle checkpoints

A

checkpoints control transitions between phases to avoid unnecessary energy waste

called cyckin dependent kinases (CDKs)

CDKs bind to respective cyclins to become active which then phosphorylate other proteins to trigger the next stage of the cycle

49
Q

CDK + associated cyclin

A

G1 to S
- CDK 4 + cyclin D

commits to replication (G1)
- CDK 2 + cyclin E

initiates replication (S)
- CDK 2 + cyclin A

promotes mitosis (G2)
- CDK 1 + cyclin B

49
Q

cell cycle phase order

A

G1 phase
G0 phase
G1/S checkpoint
S phase
S/G2 checkpoint
G2 phase
G2/M checkpoint
M phase
mitotic spindle checkpoint

50
Q

G1 phase

A

gap 1

cell active and growing

not committed to undergoing division

51
Q

G0 phase

A

gap 0

technically not apart of cycle

when cell is resting (nerve/muscles cells)

52
Q

G1/S checkpoint

A

cell proteins check for DNA damage

start point, commits cell to progression through cycle

activates signals allowing cell to divide

53
Q

S phase

A

cell replicates entire genome

centrosome duplicated

54
Q

S/G2 checkpoint

A

DNA integrity checked

55
Q

G2 phase

A

last chance for cell to grow before division

cytoplasm and cellular contents (endomembrane system) increased in preparation for division

56
Q

G2/M checkpoint

A

large scale rearrangement to structure of cell

increase in cell volume causes progression through checkpoint

57
Q

M phase (mitosis)

A

division occurs

58
Q

mitotic spindle checkpoint

A

ensure all chromosomes are properly separated preventing chromosome imbalance

ensures cytokinesis only occurs successful completion of mitois

59
Q

p53 protein

A

tumour suppressor proteins that ensures cells with damaged DNA dont divide

initiate apoptosis in cells with damaged DNA

if dysfunctional cells can evade apoptosis and replicate uncontrollable

60
Q

phases of mitosis

A
  • interphase (not a phase)
  • prophase
  • prometaphase
  • metaphase
  • anaphase
  • telophase
  • cytokinesis (not a phase)
61
Q

interphase

A

when DNA replication occurs (G1, S and G2 phase)

62
Q

prophase

A

chromosomes condense and pack into chromatids

sister chromatids connected at centromere

gene transcription stops

endomembrane system dissolves into tiny vesicles, mitochondria remain but are randomly distributed in cell

nuclear envelope dissolves, choromsomes released into cytosol

mitotic spindle forms around each centrosome

centrioles form (MTOCs)

63
Q

prometaphase

A

kinetochore forms (complex that binds to chromatids, each sister chromatid has two, one on each side)

kinetochores use ATP to polymerize and depolymerize microtubule spindle fibers allowing chromosomes to move to the center of the cell

64
Q

metaphase

A

all chromosomes arrive at spindle equator

chromosomes successfully attach to kinetochore microtubule which now pulling equally in both directions

mitotic spindle checkpoint occurs ensure proper alignment at equator

65
Q

anaphase

A

proteins binding sister chromatids cleaved, kinetochore microtubules shorten

in last anaphase chromosomes reach maximum condensation level

additional microtubule organize around spindle equator in preparation for cytokinesis

66
Q

telophase

A

reorganization of cell

nuclear membrane reform around chromosomes

interphase cytoskeleton and endomembrane system reform

67
Q

cytokinesis

A

animal cell, contractile ring forms where spindle equator was

ring tightens cell divides in half, moment when plasma membrane snaps (hydrophobic nature cause rupture to reseal spontaneously)

after occurs two new cells enter interphase

reform junctions and interior of normal cell

PHGY 170 (8 decks)

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