Molecular and Cellular Biology 181 Module 4

Many cellular processes represent work that requires the expenditure of energy. Which of the actions is not a cellular process that requires the cell to expend energy?

diffusion of water into cells.

Which of the choices is an example of potential energy?
an electrochemical gradient across the cell membrane
flow of calcium ions through a membrane channel
chemical transport, as in the sodium-potassium pump
contraction of a muscle cell

electrochemical gradient across cell membrane

The transition state is that portion of the progress of a chemical reaction with a large amount of energy found in _______ reactions.

both exo and endothermic reactions

As your text notes, in XX females the dosage of X-linked genes is twice what it is in XY males. However, the level of expression of X-linked genes is about the same in both males and females. In mammals this dosage compensation is the result of X-inactivation in females. T/F

true

In the mammalian developing female (XX) embryo, a random inactivation of either the maternally derived X chromosome or the paternally derived X chromosome results in all the cells from subsequent cell divisions expressing only genes on the active X chromosome. T/F

true

"Turning off" or inactivating the X chromosome in cells of female mammals involves production of noncoding RNA by the Xist gene found in the X chromosome inactivation center (XIC) of the X chromosome. T/F

true

Proteins produced from the Xist RNA transcripts coats the X chromosome to inactivate it. T/F

false

When lactose is removed from the growth medium, the cells continued to divide by using other nutrients that are present. The amount of b-galactosidase in the culture remains constant for 30 minutes or more. What happens to the amount of b-galactosidase per cell?

It decreases by half with each cell division.

Monod found that, when lactose was removed from the growth medium, the amount of b-galactosidase in the culture remained constant for 30 minutes or more. How can this result be explained?

b-galactosidase is stable and does not break down for at least 30 minutes.

Monod discovered that the amount of b-galactosidase enzyme produced per minute reached a maximum at a certain level of lactose and could not be increased by adding even more lactose. Which explanation is consistent with this finding?
-Translation reaches a maximum rate that cannot be exceeded.
-All of the answer options are correct.
-Transcription reaches a maximum rate that cannot be exceeded.
-The permease limits the amount of lactose that can enter the cell.

B. all of the answers are correct

In Monod's experiment, the b-galactosidase enzyme appeared almost immediately when lactose was added to a growing culture. Which explanation is consistent with this finding?
-Presence of lactose activates a pre-existing, but inactive, b-galactosidase.
-Presence of lactose stimulates transcription of the gene for b-galactosidase.
-All of the answer options are correct.
-Presence of lactose stimulates translation of a pre-existing mRNA.

All of the answers are correct