Microbiology: Cell Cycle

Question 1

How long does the S phase normally take?

Answer 1

10-12 hours

Question 2

How long does the M phase normally take?

Answer 2

1 hour

Question 3

Interphase

Answer 3

G1, S, G2

Question 4

At what phase is the cell at its lowest level of activity?

Answer 4

G1. It starts with a slightly smaller daughter cell.

Question 5

Why is biosynthetic rate so high in G1?

Answer 5

The cell is assembling the machinery necessary for DNA replication that will happen in S phase. It is also trying to get the smaller daughter cell up to speed.

Question 6

Why is the biosynthetic rate decreased during S phase?

Answer 6

There is a fixed amount of energy a cell can use. Biosynthetic rates of proteins decreases so histone synthesis rates can increase.

Question 7

What do you have at the end of S phase.

Answer 7

Two identical sister chromatids joined by a centromere.

Question 8

Why does biosynthesis increase again in G2 phase?

Answer 8

The cell synthesizes microtubules and centrosomes for the bipolar spindle apparatus.

Question 9

6 sub phases of M phase

Answer 9

Prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis

Question 10

What happens during prophase?

Answer 10

Sister chromatids begin condensing. Mitotic spindle apparatus begin aligning at polar sides of the cell.

Question 11

What pulls the centrosomes to different ends of the cell?

Answer 11

Motor proteins (dyneins and kinesins)

Question 12

What happens during pro metaphase?

Answer 12

Sudden breakdown of the nuclear envelope by phosphorylation of nuclear laminas. Kinetochore is established and microtubules attach to sister chromatids on both sides.

Question 13

What stabilizes microtubule attachment to the sister chromatids?

Answer 13

Opposite poles must establish equal tension on the centromere

Question 14

What happens during metaphase?

Answer 14

Tug-of-war of chromatids to center of cell by microtubules.

Question 15

What happens during anaphase?

Answer 15

Microtubules depolymerize and become shorter and shorter pulling chromatids apart. Centromeres polarize to opposite ends of the cell.

Question 16

What happens during telophase?

Answer 16

Chromosomes decondense, new envelop forms around each pole and contractile ring is formed.

Question 17

What composes the contractile ring?

Answer 17

Ring of motor proteins (actin) that will allow the cell to contract during cytokinesis

Question 18

What happens during cytokinesis?

Answer 18

The contractile ring pulls the cell membrane from within like a draw-string. The cells then fill in the mid body with plasma membrane and the cells separate.

Question 19

G1/S Checkpoint checks what?

Answer 19

Looking for appropriate cell size and undamaged DNA. No external inhibitory signals, only positive signals.

Question 20

G2/M Checkpoint checks what?

Answer 20

Make sure all DNA is replicated, environment is favorable, is the cell size okay and makes sure there are no external inhibitory cell signals

Question 21

Metaphase-Anaphase transition mitotic checkpoint checks what?

Answer 21

Are all the chromosomes attached and oriented in the correct fashion?

Question 22

Cell cycle regulators

Answer 22

Cyclin-dependent kinases, cyclins, cyclin dependent inhibitory proteins (CKIs)

Question 23

What determines CDK activity in cell cycle regulation?

Answer 23

They must be bound to a cyclin to be active. When active they phosphorylate targets to trigger cell cycle events.

Question 24

How do cyclins control cell cycle?

Answer 24

They are not always present. They undergo synthesis and rapid degradation. When absent, CDKs are inactive and cell cycle events do not happen. They control movement from one phase to another.

Question 25

What is the role of CDKIs?

Answer 25

They fine-tune CDK activity by forming complexes with cyclin and CDK to block activation of CDKs.

Question 26

How is cyclin activity limited at the end of mitosis?

Answer 26

Ubiquitination tags the cyclins for degradation. Then cyclins can no longer activate CDKs.

Question 27

M-CDK

Answer 27

Phosphorylates nuclear lamins to initiate nuclear envelope breakdown. Phosphorylates motor proteins on microtubules for chromatid separation.

Question 28

S-CDK

Answer 28

Phosphorylates origin recognition complex to initiate DNA replication. Phosphorylates CDC6 which leads to replication termination.

Question 29

Anaphase promoting complex (APC)

Answer 29

Signals for S and M cyclin degradation and CDK inactivation. Phosphorylates securin, protein that allows sister chromatids to separate in anaphase.

Question 30

What inhibitory signals regulate the cell cycle checkpoints?

Answer 30

p21, p27, p16 CDKIs. Activated by p53 after DNA damage or other similar events