Biology 1202-Ch.18 Quiz

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Why is the lac operon said to be an inducible operon?

When allolactose is present, it induces the inactivation of the lac repressor.

DNA methylation is a mechanism used by eukaryotes to do what?

inactivate genes

In humans, the hormone testosterone enters cells and binds to specific proteins, which in turn bind to specific sites on the cells' DNA. These proteins probably act to do what?

help RNA polymerase transcribe certain genes

It is possible for a cell to make proteins that last for months; hemoglobin in red blood cells is a good example. However, many proteins are not this long-lasting; they may be degraded in days, hours, or even minutes. What is the advantage of short-lived proteins?

Short-lived proteins enable the cells to control their activities precisely and efficiently.

miRNAs can control gene expression by what action?

binding to mRNAs and degrading them or blocking their translation

Which of these is true of the cytoplasm of an unfertilized egg?

It is an unevenly distributed mixture of mRNA, proteins, organelles, and other substances.

How do master regulatory genes function in cell differentiation?

They are often capable of changing some fully differentiated cells of different types into their particular cell type. They produce proteins that act as transcription factors to produce proteins specific to the function of the particular cell type. The transcription factors they produce coordinately control related genes. They may produce proteins that stimulate production of more of the master regulatory gene.

How do cells become differentiated?

Different genes are expressed so that different proteins are produced.

Which of the following would be most likely to lead to cancer?

amplification of a proto-oncogene and inactivation of a tumor-suppressor gene

All your cells contain proto-oncogenes, which can change into cancer-causing genes. Why do cells possess such potential time bombs?

Proto-oncogenes are necessary for the normal control of cell growth and division.

A lack of which molecule would result in the cell's inability to "turn off" genes?

corepressor

Two potential devices that eukaryotic cells use to regulate transcription are

DNA methylation and histone modification.

Which of the following best describes siRNA?

a short double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA

Which of the following statements describes proto-oncogenes?

They can code for proteins associated with cell growth.

In response to chemical signals, prokaryotes can do which of the following?

alter the level of production of various enzymes

The tryptophan operon is a repressible operon that is

turned off whenever tryptophan is added to the growth medium.

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