Pollev

You pulse label cells in culture briefly with [H3] thymidine. The cells are at all different stages of cell cycle (unsynchronized). You know that your cells complete the entire cell cycle in 24 hours, and that the S phase is 6 hours and M-phase is 2 hours.

Question 1: what fraction of cells in M phase will be labeled after you wash out the pulse and wait a few minutes?

none (0%)

You pulse label cells in culture briefly with [H3] thymidine. The cells are at all different stages of cell cycle (unsynchronized). you know that your cells complete the entire cell cycle in 24 hours, and that the S phase is 6 hours and M-phase is 2 hours.

Question 2: after several different chase (no label) lengths - 8, 9, or 10 hours -, you only find labeled cells in M when you wait 10 hours. what do you conclude?

the G2 phase is between 9-10 hours long

If a cell in the G2 phase is fused with a cell in the M phase

the G2 nucleus will enter the M phase

Cyclin concentrations are highest during which periods of the cell cycle?

late G2 and early M

Which of the following statements is NOT true regarding the wee1 gene?

The normal wee1 gene product causes the cells containing it to be smaller, hence the name "wee."

What enzyme below does diacylglycerol (DAG) recruit and activate?

protein kinase C

What role do activated steroid receptors play in the cell?

ligand-regulated transcription factors

Which of the following has NOT been identified as a second messenger?

ATP

If you break liver cells by homogenization, separate the broken cell membranes (particulate) from the cytoplasm (soluble), and add epinephrine to the soluble portion, the result will be:

no change in glycogen phosphorylase activity

Sometimes an enzyme is activated by a receptor and brings about the cellular response by generating a second messenger. Such an enzyme is called a(n)

effector

Phosphorylation of a protein can change its behavior in all of these ways EXCEPT:

it can initiate protein synthesis

Epinephrine binds to the same type of receptors in liver and smooth muscle cells. Yet liver cells break down glycogen and smooth muscle cells relax. How can the same hormone produce such different responses?

The same hormone and its second messengers activate different intracellular proteins with different functions.