Control of Eukaryotic Cell Cycle 1

Question 1

What is the cell cycle?

Answer 1

It is the ordered sequence of events that ensures duplication of the entire genome and equal partitioning of the two copies into two genetically identical daughter cells

Question 2

What is the main (basic) function of the cell cycle?

Answer 2

To duplicate the vast amounts of DNA in the nucleus which is packaged into chromosomes and then segregate these copies evenly into 2 genetically identical daughter cells

Question 3

What is the first gap phase called?

Answer 3

G1

Question 4

What happens in G1?

Answer 4

Cells prepare for DNA replication

Question 5

What is the second gap phase called?

Answer 5

G2

Question 6

What happens in G2?

Answer 6

Cells prepare for cell division

Question 7

What happens during S phase?

Answer 7

Chromosomes are replicated

Question 8

What happens in M phase?

Answer 8

Cells carry out nuclear and cytoplasmic division

Question 9

How long does chromosome replication (S phase) take?

Answer 9

10-12 hours

Question 10

What is cell division dependent on?

Answer 10

Activation and deactivation of cyclin-dependent kinase complexes and the switching between DNA duplication and DNA segregation in all cells

Question 11

What can occur is unwanted/uncontrolled cell division occurs?

Answer 11

Cancer

Question 12

What are oncogenes/TS genes?

Answer 12

A gene which in certain circumstances can transform a cell into a tumour cell

Question 13

What can chromosome segregation errors lead to?

Answer 13

Inaccurate distribution of the genetic material to the daughter cells during cell division

Question 14

What defects can chromosome segregation errors cause?

Answer 14

Gain/loss of material; gain/loss of entire chromosomes (aneuploidy)

Question 15

What does a mutation in the Wee1 gene mean?

Answer 15

That yeast cells enter mitosis too early while still too small

Question 16

Explain biochemical regulation of the eukaryotic cell cycle?

Answer 16

G1 and S phase cells mixed (G1 nucleus started replicating early); Cells in S phase contain a dominant activator of DNA replication; G2 nucleus waited and did not re-replicate its DNA and is resistant to S phase promoting factor; Interphase cell starts to segregate chromosomes early even if replication was incomplete;
Both nuclei enter mitosis synchronously even if replication is incomplete

Question 17

What are the 3 major checkpoints in the cell cycle?

Answer 17

G1/S Phase checkpoint (Restriction Point); G2/M Phase checkpoint; Metaphase/Anaphase checkpoint

Question 18

What do checkpoints do?

Answer 18

They render the transition between different cell cycle stages sensitive to the completion of key cellular tasks and to the presence of errors

Question 19

What does the G1/S checkpoint do?

Answer 19

Determines whether all conditions are favourable for cell division to proceed and checks for DNA damage

Question 20

What are the requirements for the cell in order for it to progress to the S phase?

Answer 20

It must be the appropriate size and have adequate energy reserves

Question 21

What happens if the cell does not reach the requirements?

Answer 21

The cell can halt the cycle and attempt to remedy the problematic condition or the cell can advance into the G0 phase and await further signals when conditions improve, or apoptosis can occur is DNA is damaged beyond repair

Question 22

What does the G2/M do?

Answer 22

It ensures that all of the chromosomes have been accurately replicated without mistakes or damages

Question 23

What happens if problems are detected?

Answer 23

The cell cycle is halted and the cell attempts to either complete the DNA replication or repair the damaged DNA (if it is not repairable, then apoptosis occurs)

Question 24

What does the Metaphase/Anaphase checkpoint do?

Answer 24

Checks chromosome correctly aligned and attached to the spindle microtubules

Question 25

What happens if replicated chromosomes are not correctly segregated in the Metaphase/Anaphase checkpoint?

Answer 25

Aneuploidy

Question 26

How do cyclins work in the G1 phase?

Answer 26

G1/S-cyclins bind to and activate specific G1/S-phase Cdks to help progression through the restriction point

Question 27

What do S-cyclins do?

Answer 27

They bind to specific S-phase Cdks soon after progress through the restriction point and help stimulate DNA replication, and help control some early mitotic

Question 28

What do M-phase cyclin-cdk complexes do?

Answer 28

They are inactive at the start G2 and are activated at the end of G2 and trigger entry into M phase at the G2/M transition

Question 29

How are cyclins degraded during the cell cycle?

Answer 29

Via protein ubiquitinylation

Question 30

How are ubiquitin molecules added to other molecules?

Answer 30

By E3 ubiqutin ligases

Question 31

How are ubiquitin molecules removed from other molecules?

Answer 31

Deubiquitinating enzymes

Question 32

What is the name of the cell cycle regulator that processes E3 ubiquitin ligase activity?

Answer 32

APC/C

Question 33

How is Cdk activity regulated during the cell cycle?

Answer 33

Binding to a partner cyclin and by phosphorylation

Question 34

What happens when kinases are activated?

Answer 34

They transfer phosphate groups from ATP to serine and threonine side chains on target proteins

Question 35

What is protein phosphorylation?

Answer 35

It is reversible PTM event that is mediated by opposing actions of protein kinases and protein phosphatase

Question 36

How does protein phosphorylation happen?

Answer 36

It occurs through protein kinases and consits of the addition of a phosphate group (PO4) to the polar R group of amino acids

Question 37

What does the addition of phosphate group on a protein do?

Answer 37

Modifies the protein from hydrophobic apolar to hydrophilic polar

Question 38

What does the addition of a phosphate group on an amino acid do?

Answer 38

After an amino acid is phosphorylated, it can bind molecules with other proteins and assemble and detach proteic complexes

Question 39

Since some cellular phosphate esters are phosphorproteins, how are they formed?

Answer 39

Via catalytic enzyme and ATP, with phosphate anhydride acting as a donor

Question 40

What is the name of the third protein that is required for full activation of Cdk?

Answer 40

Cdk-activating kinase

Question 41

What does Cdk-activating kinase do?

Answer 41

It adds a phosphate group to a threonine in the T loop, which enables Cdk to bind to and phosphorylate target proteins

Question 42

What binds to the active site of the cyclin-Cdk complex?

Answer 42

Target peptides

Question 43

What does the binding of target peptides to the active site of the cyclin-Cdk complex do?

Answer 43

It ensures that the target Serine/Threonine side chains are correctly positioned with respect to the g phosphate of the bound ATP

Question 44

What can inhibit the activity of Cyclin-Cdk complexes?

Answer 44

Additional phosphorylation of CDKs on inhibitory sites

Question 45

What is CDK activity controlled by?

Answer 45

Positive regulation by cyclin protein levels; inhibitory/stimulatory phosphorylation of the CDK subunit

Question 46

What is able to suppress cyclin-Cdk activity?

Answer 46

The binding of Cdk inhibitors

Question 47

What is the p27 protein?

Answer 47

A cell cycle inhibitory protein

Question 48

What is the major function of the p27 protein?

Answer 48

Stop or slow down the cell division cycle

Question 49

How is the p27 protein able to carry out its major function?

Answer 49

By inhibiting the activity of specific cyclin-Cdk complexes and prevents substrate and ATP binding

Question 50

What can the p27 protein also be classed as?

Answer 50

A tumour suppressor gene because it is often inactivated or deleted in cancer

Question 51

Where can Cdk inhibitor proteins bind?

Answer 51

Either directly at the kinase active site (blocking kinase activity by interfering with ATP binding) or near the active site (inhibiting substrate binding)