Cell Bio Chapter 20

Only once all of the checkpoint conditions have been met can a cell transition to the next cell cycle phase.

True

Cells that pass through a checkpoint can sometimes revert back to the previous phase, but only if the conditions are right to do so.

False

At which checkpoint is it most important for the extracellular environment to be favorable and for the cell to have enough nutrients and resources?

restriction point

Which of the following is NOT a condition required to pass through the G2/M checkpoint?

the availability of nutrients

Once a cell enters G0 it can never return to the cell cycle.

False

Cells in G0 are usually not very active.

False

Which of the following proteins undergoes cycles of high and low intracellular concentrations throughout the cell cycle?

cyclins

CDK activity is dependent on cyclin binding.

True

Which of the following is NOT a factor in the activation of CDKs?

CDK concentration

Full CDK activation requires the displacement of the activation loop.

True

Which of the following events does NOT occur as a result of passing through the restriction point?

production of cyclin B

The detection of mitogens causes a cell to:

grow, and head towards the restriction point.

The detection of DNA damage by p53 can trigger the cell to enter G1 pause.

True

In which of the following situations will p21 NOT be removed from the cyclin-CDK complex?

if the DNA is damaged

DNA replication must occur only once during S phase.

True

Centrosome duplication occurs before DNA replication.

False

Which of the following proteins adds inhibitory phosphates to the ATP-binding site in CDK1?

WEE1

Which of the following proteins removes inhibitory phosphates from the ATP-binding site in CDK1?

CDC25

Which of the following proteins is NOT phosphorylated by CDK1?

B cyclin

The positive feedback loop that results in rapid CDK1 activation involves CDK1 and CDC25.

True

APC/C is inhibited by the binding of CDC20.

False

The release of CDC20 from kinetochores occurs when:

all sister chromatids are bi-oriented at the metaphase plate.

When all of the sister chromatids are bi-oriented at the metaphase plate, the kinetochores are NOT under tension.

False

As soon as cohesin is cleaved:

sister chromatids are pulled to opposite pole

Put the checkpoints in sequential order starting at
the beginning of G1.

Restriction, G1/S, G2/M, metaphase/anaphase

Many rainforest plants have potential anti-cancer
properties. One such plant, P. cupana, was used to treat cancer in mice. After treatment, tumor growth was inhibited, and the cancer cells had decreased expression of cyclin D. What checkpoint of the cell cycle did the cells stop at based on this evidence?

The restriction point

Which characteristics apply to cyclins?

Bind to and activate CDKs

For a CDK to become active, two enzymes are
involved in phosphorylation status. Choose the
correct answer of how these enzymes prepare CDK for activation below:

CAK must phosphorylate, a phosphatase must remove two more phosphate groups.

The restriction checkpoint differs between
unicellular prokaryotes and multicellular
eukaryotes in that:

prokaryotes must assess extracellular resources, multicellular cells need to wait for extracellular signals.

A common treatment for breast cancer is CDK4
(and 6) inhibitors. Normally, CDK4 phosphorylates
_____, preparing the cell for _____ by transcribing
cyclin E and A, and preparing DNA replication
machinery.

retinoblastoma; S phase

However, many breast cancers will develop resistance to CDK4/6 inhibitors by acquiring mutations in the retinoblastoma protein. To allow the cell to continue to proliferate uncontrollably, these mutations cause retinoblastoma to be _____.

active regardless of phosphorylation status