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MCB - Exam 3 > Cell Cycle I > Flashcards

Cell Cycle I Flashcards

1
Q

The cell cycle is considered to be between what two time points?

A

Moment a cell is born to the moment it is the mother of 2 cells.

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2
Q

The goal of the cell cycle is to do what two things?

A
  1. Faithfully replicate organelles and the DNA in each chromosome.
  2. Produce two genetically identical daughter cells (cytokinesis).
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3
Q

Mistakes occur at a rate of 1 x 10^(-9) per replication of 6.4x10^(9) base pairs. This results in approximately how many mistakes in one cell division?

A

6

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4
Q

How many cells are there approximately in the body?

Liver cells are cycled at a rate of __ per year.

Intestinal cells live approximately how many days?

How many RBCs does a person produce per second?

__ is a disease of excessive cell proliferation.

A

3x10^(13). (30 trillion)

1.

3-4.

2.4 million.

Cancer.

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5
Q

T/F: The cell cycle control system responds to signals inside and outside the cell.

A

True.

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6
Q

Chromosome duplication occurs during the __ phase of the cell cycle.

Chromosome segregation and cell division occur during __ phase of the cell cycle.

After both phases, cell division, aka ___, occurs.

A

S (DNA synthesis) phase.

M (mitosis).

Cytokinesis.

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7
Q

What are the 4 phases of mitosis of eukaryotic cell division?

During __, chromosomes condense into rigid rods called sister chromatids.

Sister-chromatids line up at the cell equator attached to opposite poles of spindle during what phase?

During __, sister chromatids become daughter chromosomes, and are pulled to opposite poles of spindle.

During __, the spindle disassembles, and the chromosomes are packaged into separate nuclei, cytokinesis occurs.

A

PMAT (prophase, metaphase, anaphase, telophase)

Prophase.

Metaphase (metaphase plate).

Anaphase

Telophase.

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8
Q

What is the order of the four phases of the cell cycle?

What phases are part of interphase?

During this phase, __, the cell decides to either proceed further into the cell cycle or stay at a resting phase, aka __.

A

M, G1, S, G2.

G1, S, G2.

G1, G0.

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9
Q

Name the three cell cycle checkpoints and their purpose (what each checkpoint is looking for).

A

Checkpoint 1, Start Checkpoint (Between G1 and S): Is environment favorable to enter cell cycle and proceed to S phase?

Checkpoint 2, G2 to M: Is all of the DNA replicated, environment favorable to proceed to mitosis?

Checkpoint 3, Metaphase-to-anaphase transition: Are chromosomes attached to spindle and should anaphase (sister chromatid separation) be triggered to continue mitosis and cytokinesis.

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10
Q

Cdc (cell-division cycle) genes were first discovered in what organism?

In the budding type of this organism, the bud first appears at this phase, __, and grows until mitosis phase.

A

Yeast.

G1.

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11
Q

T/F: cells will continue into the cell cycle after passing the start checkpoint, even if transferred to a poor nutrient medium.

A

True.

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12
Q

Fibroblasts are a mammalian cell line used to study the cell-cycle, but these cells stop dividing after approximately how many divisions?

A

25-40.

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13
Q

This type of cell line, ___, are cells that grow forever and are useful for studying development of RBCs.

Name two examples of these types of cells.

A

Immortalized.

MEL = murine erythroleukemia cells.

HEL = human erythroleukemia cells.

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14
Q

The cell cycle control system uses a series of biochemical switches made of these proteins ___, the heart of the cell-cycle control system.

A

Cyclin dependent kinases (Cdks)

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15
Q

Cdks ___ proteins downstream to activate them and regulate cell cycle events.

One example: Cdk activity can increase activity of proteins controlling chromosome condensation and spindle assembly.

A

phosphorylate.

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16
Q

T/F: Levels of Cdks rise and fall during the cell cycle.

A

False!!! Cdk LEVELS remain constant, only their ACTIVITIES fluctuate.

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17
Q

These proteins, ___, regulate Cdks.

T/F: The levels of these proteins fluctuate during the cell cycle.

A

cyclins.

True. (hence their name “cyclin”) Therefore, expression of cyclin controls what step the cell is in the cell cycle.

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18
Q

T/F: cyclin must be bound to Cdks for Cdks to have protein kinase activity, and without cyclins, Cdks are inactive.

A

True. (Hence their name cyclin-dependent kinase).

19
Q

Name the three classes of cyclins given in lecture.

A
  1. G1/S cyclins: start cell cycle, helps trigger progression/commitment through START checkpoint. Starts in late G1 and levels drop in S phase.
  2. S-cyclins: duplicates DNA and helps stimulate chromosome duplication. Levels remain high until mitosis.
  3. M-cyclins: Activates Cdks that stimulate entry into mitosis at G2/M checkpoint. Levels drop mid-mitosis.
20
Q

Name the three vertebrate Cdks given in lecture, and name the cycle(s) that they are most active.

A

Form complexes with cyclin to make:

G1/S-Cdk: Most active during G1.

S-Cdk: Most active during S and G2.

M-Cdk: Most active during M-phase.

21
Q

___ initiates metaphase to anaphase transition.

A

APC/C

22
Q

__ blocks the active site of an inactive Cdk.

What happens when cyclin binds to the Cdk?

What enzyme makes the Cdk “fully active?”

A

T-loop.

The binding of cyclin causes the T-loop to move out of the active site, and the Cdk is partly active.

CAK (Cdk activating kinase) phosphorylates the T-loop, making the Cdk fully active.

23
Q

The level of ___ controls the changes in the cell cycle. Name two other cell cycle control mechanisms.

A

cyclins.

inhibition and proteolysis.

24
Q

These two proteins, ___ and ___, are involved with inhibiting and increasing, respectively, the activity of Cdks.

What do these two proteins do to the Cdks?

A

Wee1 kinase and Cdc25 phosphatase.

Wee1 kinase phosphorylates “roof” site of Cdk. Cdc25 phosphatase dephosphorylates “roof” site, increasing Cdk activity.

25
Q

p27 is this kind of protein? What subunit(s) do these proteins attach to? What Cdks do these proteins primarily control?

A

CKI (Cdk Inhibitory protein).

CKIs bind to both the Cdk and the cyclin.

CKIs primarily control the two early Cdks (G1/S-Cdk and S-Cdk)

26
Q

This CKI, ___, is involved in the G1 phase of the cell cycle and a mutation, causing loss of activity, is associated with familial hereditary melanoma.

A

INK4A.

27
Q

Is p53, which influences the expression of many genes, a tumor suppressor or CKI?

Does p53 upregulate or downregulate p21?

What is the normal function of p21 and what happens if p53 function fails?

A

p53 is a major tumor suppressor.

p53 upregulates p21.

p21 is a CKI to stop cell division. No p53 function results in lower p21 expression and will lead to cancer.

28
Q

This process, ___, done to CKI’s, can turn on S-Cdk’s.

This process can be aided by this protein, ___, which adds ubiquitin to phosphorylated CKIs in G1 phase.

A

proteolysis.

SCF-ubiquitin ligase.

29
Q

This Cdk, ___, which also induces S cyclin production, is important to move through START.

This complex, ___, is important to start DNA replication.

A

G1/S-Cdk

S-cyclin-Cdk complex

30
Q

The ___ subunit helps SCF recognize target proteins.

A

F-Box

31
Q

Towards the end of G2 phase, before M phase, a lot of primed cyclin-M-Cdk complexes are formed. These are inactive. What protein activates them?

A

Cdc25 protein phosphatase (removes inhibitory phosphates).

32
Q

When M-Cdk becomes active, what two things occur that result in a double-circuit positive feedback loop, resulting in fast M-Cdk activation?

A
  1. Activates Cdc25 phosphatase to remove inhibitory phosphate from roof site.
  2. Inhibits Wee1 kinase, which is responsible for adding the inhibitory phosphate.
33
Q

What triggers the mitosis progression from metaphase to anaphase?

The key regulator of this process is this protein.

A

protein destruction (NOT PROTEIN PHOSPHORYLATION).

APC/C (anaphase-promoting complex)

34
Q

APC/C is a member of the ___ family of enzymes. Its activation affects these two chromosomal proteins.

A

ubiquitin ligase.

cohesin and securin.

35
Q

Sister chromatids are glued together by ___.

___ protects the above protein by inhibiting what other protein?

APC/C levels rise in mid-mitosis, causing the destruction of ___. That destruction allows ___ to undo the glue holding chromatids together (cleaves cohesin).

A

Cohesin.

Securin. Securin protects cohesin by inhibiting separase.

Securin. Separase.

36
Q

Inactive APC/C is activated by binding to ___. APC/C also destroys all of the ___ in the cell cycle.

A

Cdc20.

Cyclins.

37
Q

Why does APC/C, when the cell goes into anaphase, get rid of S-cyclins and M-cyclins?

A

Because we don’t want more DNA and chromosomes.

38
Q

List the 5 steps of the cell cycle control system.

A
  1. G1-Cdk activation.
  2. G1-Cdk stimulates genes making G1/S-cyclin + S-cyclin.
  3. G1S-Cdk activity induces S-Cdk activity (DNA replicates)
  4. M-Cdk drives expression through G2/M checkpoint (triggers prophase, metaphase, assembly of mitotic spindle, attachment to sister chromatids).
  5. APC/C and Cdc20 triggers destruction of securin and cyclins (at metaphase-anaphase transition).
39
Q

How many times does S-Cdk initiate DNA replication per cycle?

A

Once.

40
Q

What two events occur during the G1 and S phase of the cell cycle with regards to DNA replication?

A
  1. Prereplicative complex (Pre-RC) assembles at origins of replication during the G1 phase.
  2. Replication forks are created during S phase.
41
Q

Between G1 and what other timepoint are no new Pre-RCs formed?

A

No new Pre-RCs are between G1 and the next G1 cycle.

42
Q

Assembly of Pre-RC is inhibited by __ activity.

A

Cdk

43
Q

No Pre-RC is formed during __ stage and __ stage, even though S-CDk and M-Cdk are high.

A

S stage and M stage.

MCB - Exam 3 (11 decks)

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