Ch. 9 Advanced

_________ operons often contain genes coding for anabolic enzymes and are usually turned off by the end product of the reactions catalyzed by these enzymes.

Repressible

The mechanisms of _________ transformation involve genes that can regulate cellular genomes and control the onset of cell division.

oncogenic

A(n) __________ is a section of prokaryotic DNA that contains one or more genes along with a corresponding operator to control transcription.

operon

Gene expression in prokaryotes is regulated through _______.

operons

Prokaryotic DNA is arranged into systems called _____

operons

The _____ protein is capable of repressing an operon.

repressor

While studying the infection process and life cycle of a newly discovered virus, it was determined that the virus never entered the nucleus of the host cell. This virus may have any of the following genomes except DNA. single (+) strand RNA. double-stranded RNA. single (-) strand RNA.

DNA

All viruses require the use of host cell ribosomes and host cell tRNA to translate viral mRNA into viral proteins. T/F

T

An operon is a group of genes that is under the control of a singe operator site. T/F

T

Repressible operons are normally turned on in the cell. T/F

T

Which part of the control locus acts as an on/off switch for transcription?

operator

Two components of an operon include the ___________ that acts as an on/off switch, and the _____________ gene sequences.

operator structural

Which are components of an operon in a sequence of DNA? RNA polymerase inducer repressor operator structural genes

operator structural genes

The ______ is the gene that codes for a protein capable of repressing the operon.

regulator

True or false: Viral genomes are always composed of either single or double stranded DNA.

F

Which of the following is the genetic pattern of viral genomes?

Single or double stranded DNA or RNA

Place the steps of replication of a dsDNA virus in the correct order, from viral penetration to assembly of mature virus particles.

Viral DNA enters a host nucleus. Viral DNA is transcribed into mRNA. Viral mRNA is translated by host ribosomes. Viral DNA is replicated in the nucleus. Viral DNA is packaged into capsids.

_______ of positive-strand ssRNA requires the synthesis of a negative strand which becomes a master template to create new daughter strands.

replication

The protein product of a repressor gene is the __________ which binds the operator to stop transcription.

repressor

The protein product of a repressor gene is the ___________ which binds the operator to stop transcription.

repressor

The analysis of the nitrogenous bases of the nucleic acid of a newly discovered virus showed 20% adenine, 40% guanine, 10% thymine, and 30% cytosine. The viral nucleic acid is most likely

single-stranded DNA.

Short lengths of RNA called __________ have the ability to control the expression of certain genes.

small interfering RNA (siRNA)

True or false: The promoter of an operon is the location where RNA polymerase binds, whereas the operator acts as the on/off switch for transcription of the structural genes.

T

Short interfering RNAs affect gene expression in eukaryotes by

blocking the action of other RNAs.

Transcription of the structural genes of the arg operon is inhibited when arginine

builds up and binds to and activates the repressor.

Viruses require host transcription machinery because they do not have their own RNA polymerases. T/F

F

Control mechanisms ensure that _____ are active only when their products are required.

genes

Which is incorrect about inducible operons?

have genes turned off by a buildup of end product

The arg operon is usually transcriptionally active because the repressor is ______ until the levels of arginine ______.

inactive; build up

The ______ protein is capable of repressing an operon.

repressor

Which of the following are true of RNA viruses compared to DNA viruses? Smaller genomes Virus cycle occurs in cytoplasm Enter host cell in RNA form Virus cycle occurs in nucleus

Smaller genomes Virus cycle occurs in cytoplasm Enter host cell in RNA form

Which are parts of the lactose operon? Control locus Regulator Corepressor Structural locus

Control locus Regulator Structural locus

dsDNA

Herpesvirus

Which viruses insert their DNA into the host genome increasing the risk of cancer? Herpesvirus Ebola virus Hepatitis B virus

Herpesvirus Hepatitis B virus

_________ operons are usually turned on by the substrate of the enzyme for which the structural genes code.

Inducible

Which type of operon is typically in the "off" position until the appropriate substrate is present?

Inducible operon

Select all of the true statements about RNA viruses.

Positive-strand genomes are ready to be translated into protein. Negative-strand genomes must be converted into positive strands before translation. Positive-strand genomes can be converted into dsRNA genomes.

What is the term for the gene that codes for a protein capable of repressing the operon?

Regulator

Viral DNA inserted into the host genome may cause the transformation of the host cell into a _________ cell.

cancer

Inducible operons often encode __________ enzymes, while repressible operons often encode __________ enzymes.

catabolic, anabolic

The lactose operon is composed of the regulator, the ______ locus, and the structural locus.

control

A ______ binds to an inactive repressor to make an active repressor.

corepressor

In eukaryotic cells, gene expression is regulated in response to ______ stimuli such as nutrient and toxin levels, and also during growth and ________

environmental development

A(n) ___________ operon, such as the lac operon, is usually in the "off" position, but can be turned on when the appropriate substrate is present.

inducible

Transcription of the structural genes of the lac operon will be inhibited when

lactose concentration is low and glucose concentration is high.

Transcription of the structural genes of the lac operon will be greatest when

lactose is present in high concentrations but glucose is absent.

Replication of the genome of DNA viruses occurs in the __________, whereas replication of the genome of RNA viruses occurs in the __________.

nucleus; cytoplasm

Several DNA viruses are known to be initiators of cancers and are thus termed __________

oncogenic

ssRNA

poliovirus

The ________ of an operon is the location where RNA polymerase binds, whereas the _________ acts as the on/off switch for transcription of the structural genes.

promoter/operator

Retroviruses contain the enzyme ________

reverse transcriptase

_______ genes code for proteins.

structural

The ssRNA of positive-strand viruses come ready to be ______ into proteins.

translated

Put the following steps in order describing the viral process of a retrovirus, such as HIV.

viral rna ss dna ds dna new viral rna

What binds with an inactive repressor to make an active repressor?

Corepressor

In a repressible operon, excess product acts as a corepressor to increase transcription of the operon. T/F

F

_______ RNA may exert control on several levels in both prokaryotes and eukaryotes.

Regulatory

Which type of organisms have their DNA arranged into operons?

eukaryotes

Lactose is a corepressor in the lac operon. T/F

f

retrovirus

hiv

Synthesis of an inducible enzyme requires

substrate bound to repressor

Synthesis of a repressible enzyme is inhibited by

the corepressor-repressor binding to the operator

Riboswitches exert effects on __________ whereas repressors and inducers exert effects on __________.

translation; transcription