Exam 4 Lecture 1: Cell Cycle I

Question 1

Which kind of cells are the most abundant in your body?

Answer 1

RBCs / erythrocytes are the most abundant type of cell in your body in total cell count

Question 2

Explain what happens in S phase and how long it takes

Explain what happens in M phase and how long it takes

Answer 2

S phase: DNA synthesis (10-12 hours)

M phase: Mitosis (nuclear division) and cytokenesis (cytoplasmic division) takes roughly 1-2 hours

Question 3

What steps make up interphase?

Answer 3

Interphase: G1, S, G2

and then mitosis completes the cell cycle

Question 4

What are the four phases of the cell cycle?

what is the specialized resting state that some cells get stuck in?

Answer 4

Four phases: G1, S, G2, M

Go is a specialized resting state that some cells get stuck in, it is essentially when they never leave G1

Question 5

Mitosis: splitting of the ______

Cytokinesis: splitting of the ______

Answer 5

Mitosis is splitting of the nuclei

cytokinesis is splitting of the cytoplasm

Question 6

What is the longest phase in the cell cycle?

Answer 6

Longest phase in the cell cycle is S phase

Question 7

What are some model systems used to study the cell cycle?

Answer 7

Xenophus (frogs)

Cell and Cell Free systems

Yeast

Question 8

Explain HeLa cells

Answer 8

They are “immortilized”, never have a Go phase

continually proliferate

Question 9

The time required for the cell cycle phases is remarkably consistent between cells and even between different organisms. This results in _______ of division in developing organisms

Answer 9

The time required for the cell cycle phases is remarkably consistent between cells and even between different organisms. This results in apparent synchronization of divisions in developing organisms.

Question 10

The cell cycle is controlled by the products of ____ genes. Mutational studies have demonstrated which genes orchestrate each part of the cell cycle

Answer 10

Cell cycle is controlled by the products of cell division cycle genes (CDC genes)

Question 11

Cells that are synthesizing DNA in S phase can be identified by the incorporation of a ________

Cells that are not in S phase appear red

Answer 11

Cells that are making DNA in S phase can be identified by the incorporation of a fluorescently labeled thymidine analog (BrdU green)

Question 12

The DNA content doubles during _____, so researches can staing the DNA and measure the brightness of each cell using a cytometer

Answer 12

DNA doubles during S phase

you can stain DNA and measure brightness with cytometer

Question 13

What are the three major checkpoints in the cell cycle

Answer 13

Checkpoints in the cell cycle:

Start checkpoint at end of G1 to enter S phase

G2/M checkpoint

Metaphase to Anaphase transition

Question 14

Explain what cyclin dependent kinases do

Answer 14

Cyclin dependent kinases (Cdk’s) are enzymes that phosphorylate cell cycle machinery at the appropriate time. The activity of Cdk’s is controlled by a regulatory partner cyclin. Without cyclin, Cdk’s are inactive.

There are G1/S Cdk , S-Cdk, and M-Cdk’s

level remains same at all time, its their activity that changes

Question 15

Cdk activity is also regulated by the ___________ at multiple sites. One site activates the kinase, while another deactivates it.

Cdk activity is also decreased by _____

Answer 15

Cdk activity is also regulated by phosphorylation of the kinase itself at multiple sites. One site activates the kinase, the other deactivates it.

Cdk activity is also decreased by Cdk inhibitor proteins (CKIs)

Question 16

Explain how unfavorable conditions inhibit Cdks

Answer 16

Question 17

Explain the activation of M-Cdk

Answer 17

Feedback mechanisms control the activity of Cdk. Cdk phosphorylates a phosphatase, which removes the inhibitory phosphate on Cdk

M-Cdk activates its own activator (CAK) and inactivates its own inactivator (Wee1). Allows abrupt and complete activation and inactivation of the cell cycle.

Question 18

Explain the checkpoints by explaining what the cell is looking for at each spot

Answer 18

Start Checkpoint (end of g1): is the enviornment favorable to start DNA synthesis?

G2/M checkpoint: is all the DNA replicated? and is the enviornment favorable to enter mitosis?

Metaphase to Anaphase transition: are all of the chromosomes attached to the spindle?

Question 19

Explain the Initiation of DNA Replication:

Its accomplished by the formation of a large multiprotein complex called the ________, which binds to specific regions of DNA and initiates the recruitment of a prereplicative complex. This complex is composed of _____

Answer 19

Initiation of DNA Replicaiton:

Accomplished by formation of large multiprotein complex called the “origin recognition complex (ORC)” which binds to specific regions of DNA and initiates the recruitment of a prereplicative complex. This complex is composed of DNA polymerase and other replication proteins such as helicase, which unwinds DNA and allows replication to begin.

Question 20

What is so important about the G2/M checkpoint?

Answer 20

It allows for the cell to check and make sure the DNA is replicated and that the DNA is NOT damaged/is of quality to proceed to mitosis.

Question 21

Most important checkpoint?

Answer 21

Start checkpoint: G1/S checkpoint

Question 22

What happens during the beginning of M phase?

Answer 22

Beginning of M phase:

M-Cdk is “stockpiled”

Induces assembly of mitotic spindle

Triggers chromosome condensation

Initiates breakdown of the nuclear envelope

Question 23

Explain prophase

Answer 23

Prophase:

• the replicated chromosomes (each containing two sister chromatids) condense.
• Outside the nucleus, the mitotic spindle assembles

Question 24

Sister chromatids are held together by ____

It’s important that they stay together so that they can be found by the spindle apparatus and segregated to opposite poles

Answer 24

Sister chromatids are held together by cohesins

Question 25

Explain condensin

Answer 25

Condensin is a five subunit complex that is structurally similar to cohesin. It supports the condensation of the DNA. This is important because otherwise the DNA would get tangled up and break during segregation in anaphase.

Question 26

Explain what happens in prometaphase

Answer 26

Prometaphase: starts abruptly with the breakdown of the nuclear envelope. Chromosomes can now attach to spindle microtubules via their kinetochores and undergo active movement.

Question 27

Explain what happens during metaphase

Answer 27

Metaphase: chromosomes are aligned at the equator of the spindle, midway between the spindle poles.

The kinetochore microtubules attach sister chromatids to opposite poles of the spindle.

Question 28

Explain what happens during anaphase

Answer 28

Anaphase: the sister chromatids seperate to form daughter chromosomes, and each is pulled apart toward spindle pole

Kinetochores get shorter, spindle poles move apart

Question 29

Explain what happens during telophase

Answer 29

During telophase:

two sets of daughter chromosomes arrive at poles of the spindles and decondense.

two distinct nuclei

Question 30

During cytokinesis:

the cytoplasm is divided in two by a contractile ring composed of _____ and ____ (and also ____), which pinches the cell in two to create two daughter cells, each with one nucleus

Answer 30

Cytokinesis:

contractile ring is composed of actin and myosin filaments

(and septins)

Question 31

Cdc15 mutation leads to a cell that____

Answer 31

Cdc15 mutation: cell gets stuck in anaphase