BSC2010 Ch. 11

Which of the following statements describes the process regulated by the lac operon?

Buildup of a small molecule induces expression of the enzymes that metabolize the small molecule.

Operons

Consist of a promoter, an operator and two (or more) structural genes

_____ genes are expressed at a constant rate most of the time

Constitutive

Epigenetics may be defined as changes in the expression of a gene or set of genes by ____ and _____

DNA methylation; chromosomal protein alteration

Which statement about RNA polymerase is true?

Eukaryotes use different RNA polymerases to transcribe rRNA and mRNA

What is the function of the operator region of the trp operon?

Provides a site for the repressor to bind

In the initiation of the transcription of protein-coding genes in eukaryotes, ____ cannot bind directly to ____. Initiation requires ___ and the other regulatory proteins called ____.

RNA polymerase II; the initiation site; TFIID; transcription factors

Which of the following is/are not involved in the process of transcription?

Ribosomes

Gene expression cannot be regulated

during replication

Structural genes

encode proteins not involved in gene regulation

A retrovirus

encodes a reverse transcriptase

A(n) ____ operon is turned off unless needed

inducible

A(n) ____ operon is turned on unless not needed

repressible

Bacterial viruses (phages)

require a host cell to replicate

____ are present in prokaryotes and bind to and direct the polymerase to specific promoters

Sigma factors

Predict what would happen to the synthesis of the enzyme HMG CoA reductase (an enzyme that catalyzes an initial step in the synthesis of cholesterol) if trichostatin A, a histone deacetylase inhibitor, is added to liver cells

The amount of HMG CoA reductase would increase

A student claims that the lac operon is an example of a mechanism that an organism uses to conserve energy. Evaluate the validity of the student's claim.

The claim is valid because the lac operon allows a bacterial cell to shut down a metabolic pathway if it is not immediately needed.

How does a repressible system such as the trp operon compare to an inducible system such as the lac operon?

The repressible system involves repression of gene expression in response to a signal; the inducible system involves activation of gene expression in response to a signal

Refer to the table below. A student constructed the table as a study guide. He summarized the activities of the various components of the trp operon under low and high tryptophan conditions. Evaluate the accuracy of the information shown.

The repressor gene is expressed at the same level under high and low tryptophan levels.

Which of the following does not regulate gene expression after transcription?

Transcription factor binding

Under what conditions does the trp repressor become active?

When it binds to the tryptophan

In the _____ of lactose, the lac ____ binds to the lac _____ site

absence; repressor; operator

Regulation of gene expression during the phage lytic cycle does not include

enhancement of the host's gene transcription

Refer to the figure below. A mutant E. coli cell expresses z, y, and a genes at the same levels in the presence and absence of lactose. These levels correspond to those observed in wild-type E. coli cells in the presence of lactose. Which region of the DNA shown in the figure could contain the mutation?

i

DNA methylation

involves the modification of the pyrimidine cytosine

The expression of the lac structural genes is ____ when lactose is absent from the culture medium and is ____ when lactose is added, because lactose binds to the_____ and inactivates it

low; high; lac repressor

Prokaryotes and eukaryotes differ in transcription inthat

there are three RNA polymerases in eukaryotes

An enzyme adds a(n) _____ tag to proteins that are recognized by proteasomes for destruction

ubiquitin