Lecture 20 Flashcards by Valerie Solinap

What phase of the cycle is where the cell grows in size?

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What phase of the cell cycle arrests cells that do not actively go through the cell cycle?

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What phase of the cell cycle where DNA is replicated?

S phase

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What phase ensures and checks that the cell is ready to undergo cellular division?

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What are cyclin-dependent kinases (CDKs)

cell-cycle stage-specific small protein kinases that require a regulatory cyclin subunit for their activity

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Function of CDKs between after the end of G1 and before the start of S-phase?

duplicate centrosomes

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What will M-phase specific CDKs trigger?

the actual splitting of centrosomes to opposite poles of the cell = becomes spindle poles

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What are the phases in interphase?

G1, S, G2

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Which phase do microtubules attach to the chromosomes?

prometaphase

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After DNA replication, what are the two sister chromatids held together by?

cohesins

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What are cohesins?

protein complexes

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What is a centromere?

a DNA sequence in the center of the chromosomes

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What is a kinetochore?

a protein complex that binds to the centromere and to the (+) ends of the kinetochore specific microtubules as well

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What are the three major classes/types of microtubules in cell division?

kinetochore MTs, astral MTs, and polar MTs

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What are astral MTs? What do they attach to

radiate behind the spindle poles and anchor onto plasma membrane maintaining the separation of poles

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What are polar MTs?

MTs that come to the middle of the cell but do not attach to a chromosome, their distal ends will overlap the other polar MTs from the other spindle pole

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What phase in mitosis are chromosomes captured and oriented?

prometaphase

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What occurs once kinetochore MTs attaches to the kinetochores on the chromosome?

orientation begins

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What is congression?

the assembly/disassembly of MTs from each spindle pole to get the chromosome oriented correctly = back and forth pull

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What happens if congression isn’t correctly done?

can lead to translocation due to one of the MTs not correctly attached to chromosome

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Which motor proteins specifically help with congression?

Kinesin-13 and dynein

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How does the MTs move?

via assembly/disassembly of the tubulin protofilaments

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What does it mean to “capture” the chromosome?

to get it in the direct middle of the dividing cell

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What is the chromosomal passenger complex?

basically part of the kinetochore complex, proteins that fit over the MTs in a sleeve-like manner

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Function of chromosomal passenger complex?

regulates MT attachment at kinetochores

What special kinase is involved with the chromosomal passenger complex?

aurora B kinase

what is the function of aurora B kinase?

phosphorylates chromosomal passenger complex to inhibit tight MT attachment

Why would you want aurora B kinase to inhibit strong MT attachment to your chromosomes?

in the cases prior to prometaphase, ensure that the chromosomes are oriented and captured properly before MTs tightly bind to them

When does aurora B phosphorylate?

when the chromosome is not under tension and the aurora B's are close to phosphorylate each other

What causes the tension in the chromosomes?

congression

How does Anaphase A move chromosomes to poles?

via MT shortening

what ends can kinesin-13 disassemble from?

from (+) or (-) ends

What do polar MTs do to help in Anaphase?

separate/push spindle poles away from each other via kinesin 5 (sliding kinesin)

How are astral MTs anchored?

via dynein (goes towards (-) end) = toward the spindle poles (MTOC)

What are the two parts of Anaphase?

A and B

What happens in Anaphase A?

chromatids are actually separating

What happens in Anaphase B?

the cell is pushing the spindle poles in opposite directions to make sure everything is separated from each other

What type of kinases is CDKs?

Serine and threonine, NOT Tyrosine

How are CDKs regulated?

by phosphorylation or dephosphorylation or degradation via ubiquitin

When are cells irreversibly committed to cell cycle?

at the restriction point/START

What phase marks the commitment of cells to the cell cycle?

S-phase because you don't want double sets of DNA in one cell

Which transcription factor is associated with metazoans (our) restriction point?

E2F

How can E2F be inactivated?

when Rb (retinoblastoma) is bound to it

What cyclins are involved with entry into the cell cycle?

Cyclin E or A

What activates cyclin D with associated CDKs?

growth factors - messages from other cells

What is the function of cyclin D CDKs?

phosphorylates Rb to remove it from E2F to initiate transcription

Function of E2F

transcription factor that can initiate the transcription of cyclin A or E

What represents the restriction point?

cyclin A/E CDK

One of the functions of cyclin E/A with CDK?

keeps Rb phosphorylated

At what phase will the centrosomes separate from each other?

Mitosis

What CDK triggers the duplication of chromosomes?

CDK2

When does centrosome duplication start and end?

right after G1 and just at the end of G2 (goes thru S-phase)

When is the APC/C (anaphase promoting complex) active?

At 2 different points in the cycle: activated to promote anaphase and within anaphase, and at the exit of M-phase

What is the anaphase-promoting complex? (APC/C)

it is a ubiquitin ligase

What is the function of APC/C?

to degrade S-phase and mitotic CDKs after their phases are over

What is the purpose of Cdh1?

to activate APC/C

What is the S-phase cyclin-CDK complexed within G1?

Sic1

What is Sic 1?

a protein that prevents DNA replication until everything in G1 has been completed and the restriction point has been passed, acts like a checkpoint in a way

How can the cell cycle be regulated where we don't go backward or jump phases?

via phosphorylation/dephosphorylation and proteasomal degradation of CDKs

At what phase is DNA replication prepared?

In G1, how does the cell cycle prepare for DNA synthesis?

origin-recognizing complex binds to the origin of replication and helicases bind to the complex = everything is loaded but nothing is active

What activates DNA replication in S-phase?

S-phase CDKs via phosphorylation

How do cohesins work?

accessory proteins load cohesins onto the unreplicated strand so that the replicated strand will go through within the cohesins

What associates at the centromere post S-phase (G2 phase)

protein phosphatases

What is the function of protein phosphatases for chromosomes during G2?

protein phosphatases will protect cohesin-centromere pair from becoming phosphorylated so that it does not fall off like the rest of those on the chromosome

Why are protein phosphatases necessary in G2?

G2 is before mitosis = need to keep sister chromatids together before mitosis starts

When does the nuclear envelope breakdown?

prometaphase

What happens in telophase

contractile ring assembly, nuclear envelope reassembly