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MBB 231 > lec 10- The cytoskeleton > Flashcards

lec 10- The cytoskeleton Flashcards

1
Q

what are the three types of cytoskeletal elements?

A

-Microtubules (move vesicles)
-microfilaments/actin filaments (help with motility)
-intermediate filaments (structural support)

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2
Q

what type of polarity do epithelial cells have?

A

apical-basal polarity

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3
Q

which cytoskeletal component is the largest?

A

microtubules

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4
Q

what are the two types of microtubules and what do they do?

A

cytoplasmic microtubules- found in cytosol and maintain nerve cells, move vesicles, formation of spindles, maintaining or altering cell shape
Axonemal microtubules- include the organized and stable microtubules found in the structure specialized for movement such as cilia, flagella, basal bodies to which cilia and flagella attach

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5
Q

what is the axoneme?

A

the central shaft of a cilium or flagellum, is a highly ordered bundle of MT’s

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6
Q

what is the structure and composition of microtubules (MT)?

A

MT are straight, hollow cylinders of varied length that consist of usually 13 longitudinal arrays of polymers called protofilaments

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7
Q

what makes protofilaments?

A

alpha-beta-heterodimers

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8
Q

how are a-tubulin and b-tubulin binded together to form a heterodimer?

A

by non-covalent bonds

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9
Q

what do MAPs (microtubule associated proteins) do?

A

have one domain attached to microtubule while other protrudes out as a tail, they stablilize the microtubule and help it take shape

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10
Q

how is MAP activity controlled?

A

MAP activity is controlled by the the addition or removal of the phosphate groups from amino acid residues

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11
Q

which MAP is responsible for alzheimers disease when it has high levels of phosphorylation?

A

tau

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12
Q

which type of binding sites do a-tubulin and b-tubulin have?

A

a-tubulin: has only a GTP binding site
b-tubulin: has both GTP and GDP

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13
Q

why do the ends of protofilaments have charges resulting in a polarity?

A

it is due to the dimers in the MT being oriented the same way

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14
Q

which tubulin when exposed results in minus and plus end?

A

alpha exposed makes the end negative, while beta makes it positive

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15
Q

in what patter do microtubules extend outwards to support the cells shape?

A

a radial array, resulting in round flattened shape

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16
Q

can microtubules also play a key role in maintaining the internal organization of cells?

A

yes

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17
Q

which drugs depolarize or disassemble microtubules?

A

colchicine and nocodazole

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18
Q

what happens to the golgi when the disassembling drugs are used on the microtubules?

A

disperses the golgi into seperate stacks scattered throughout the cytoplasm

19
Q

which motor proteins that bind to microtubules move vesicles anterograde (forward) and retrograde (backward)?

A

kinesin and dynein

20
Q

what does myosin do?

A

it is a motor protein that attaches to actin filaments and helps move them

21
Q

what do molecular motor proteins convert?

A

convert energy from ATP to mechanical energy

22
Q

what is the chemical cycle steps that helps motor proteins move microtubules/actin filaments?

A

binding of ATP, hydrolysis of ATP, release of ADP and Pi, binding of new ATP

23
Q

do motor proteins have momentum?

A

no, once the energy is used up they come to an immediate stop

24
Q

what movement mechanism does kinesin use?

A

“hand over hand” mechanism

25
Q

can kinesin and dynein be binded simultaneously by an organelle?

A

yes, they can both move across the same microtubule, one above while the other below

26
Q

can motor proteins regulate the dispersal of melanosomes?

A

yes, dynein aggregates it while kinesin disperses it

27
Q

what determines the microtubules dynamic instability?

A

the growth of a microtubule is if there is a large concentration of GTP bound free tubulin, low concentration means shrinking of microtubule

28
Q

where do microtubules form and from which side do they start growing?

A

form from microtubule organizing centers and they start growing from the negative side

29
Q

what is a centrosome?

A

a microtubule organizing center

30
Q

what are the stages in the cell cycle?

A

G1- cell grows and carries out normal metabolism, organelles duplicate
S- DNA replication and chromosome duplication
G2- cell grows to prepare for mitosis
M- mitosis: prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis

31
Q

how long does the M phase and the interphase (G1, S, G2) last for?

A

M phase- an hour or so
Interphase- days, weeks, or longer

32
Q

what are the steps of Mitosis?

A

prophase- chromosomes condense and spindles are formed, nuclear envelope is dispersed
prometaphase- microtubules connect to kinetochores of chromosomes, chromosomes move to spindle equator
metaphase-chromosomes are alligned in the middle of microtubules from one side to the other, both poles
anaphase- centromeres split, and chromatids seperate, spindles move apart
telophase- chromotids cluster at opposite ends of spindle, daughter cell formed by cytokinesis

33
Q

what is centrosomes made of?

A

-yTURCS (tubulin ring complex), where nucleation occurs
-centrosome matrix
-centrioles (short cylinder of modified microtubules)

34
Q

from which end to what does the microtubule grow?

A

”-“ end to “+” end

35
Q

what is the yTURC made of?

A

y-tubulin

36
Q

what are the three classes of microtubules in a spindle?

A

kinetochore microtubules- are connected to chromosomes
Astral microtubules- project toward the cell cortex and interact with it thereby orienting the spindle of division
polar microtubules- interact with microtubules from the opposite pole of the cell

37
Q

what are the three components of the nuclear envelope?

A

nuclear pores, nuclear lamina (composed of intermediate filaments), and nuclear membranes

38
Q

what happens to the nuclear envelope in prophase?

A

the three parts of the nuclear envelope is disassembled in different processes:
-the membrane is disrupted by dynein making wholes tearing it apart
-phosphorylation of human lamin causes depolymerization of the intermediate filaments in the nuclear lamina

39
Q

what happens in prometaphase?

A

-mitotic spindle is formed and chromosomes are moved by microtubules into the center of the cell, a single kinetochore is attached to microtubules from both spindle poles
-the metaphase plate is generated by a tug of war between two centrosomes
-microtubule plus end can polymerize or depolymerize
-microtubule negative end can only depolymerize

40
Q

what is a kinetochore?

A

a complex of proteins that associate with the centromere off a chromosome, “+” end of microtubules attach to the kinetochores

41
Q

what happens in metaphase?

A

metaphase occurs when chromosomes are aligned at metaphase plate

42
Q

what happens in anaphase?

A

-tubulin subunits are lost from both ends of kinetichore microtubules, and lost from minus end of polar microtubules, then added to plus end of polar microtubules
-motor proteins push polar microtubules apart

43
Q

what happens in telophase?

A

spindle is disassembled, nuclear envelopes are reassembled, chromosomes become dispersed, cytoplasm is split between both daughter cells in a process called cytokinesis

44
Q

what happens in cytokinesis?

A

-a signal is released from the spindle midzone
-a belt-like bundle of actin filament (ring) forms just below the plasma membrane in early anaphase
-cleavage progresses and ring tightens around cytoplasm
-contraction of ring is generated by interaction between actin and myosin motor protein

MBB 231 (17 decks)

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