Gene Regulation

5/29/13 Gene Regulation & Viruses

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Gene Regulation & Viruses

Due: 3:00pm on Monday, May 6, 2013

Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy

Regulation of Gene Expression in Bacteria

The operon model describes how bacteria control the production of groups of enzymes. In this model, synthesis of the messenger RNA coding for theseenzymes is switched on or off by regulatory proteins.

Part A - Operon vocabulary

Can you match terms related to operons to their definitions?

Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

Hint 1. Overview of operon control

An operon consists of a group of related genes that are transcribed into a single messenger RNA molecule from a single promoter. The switchthat controls the transcription of an operon is a segment of DNA called an operator, which is usually part of the promoter.An operon is regulated by a regulatory protein that is transcribed from a regulatory gene outside of the operon DNA. The regulatory protein canbe an activator, which in its active form stimulates gene transcription, or a repressor, which switches off the operon. However, a repressor canbe inactivated when a small molecule called an inducer binds to the repressor, altering its conformation.

Hint 2. Review of transcription

Transcription is the synthesis of RNA using DNA as a template. In bacteria, RNA polymerase binds to a stretch of DNA called a promoter. RNApolymerase then moves along a continuous stretch of DNA, synthesizing RNA.

Hint 3. What are the parts of an operon?

Drag the labels to their appropriate locations on the diagram of an operon. Labels can be used once or not at all.

ANSWER:

ANSWER:

Biol 1002 - Spring 2013

Gene Regulation & Viruses Resources

Signed in as Nora Trejos Help Close



Correct

An operon is made up of a promoter and the genes of the operon. The promoter, which includes an operator, is the stretch of DNA where RNApolymerase binds. Regulatory proteins bind to the operator. The genes of the operon code for a related set of proteins. A regulatory gene locatedaway from the operon codes for a protein that controls the operon.

Part B - Regulation of model operons

The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons?

Sort the statements into the appropriate bins depending on whether or not each operon would be transcribed under the statedconditions.

Hint 1. How are operons regulated?


ANSWER:



Hint 2. How is the trp operon regulated?

How is the trp operon regulated?

Select the three statements that apply.

ANSWER:

Hint 3. How is the lac operon regulated?

How is the lac operon regulated?

Select the four statements that apply.

ANSWER:

ANSWER:

The trp operon undergoes negative control.

When glucose is present, it binds to catabolite activator protein (CAP), which stimulates transcription of the operon.

When tryptophan is absent, the regulatory protein is active.

When tryptophan is absent, the regulatory protein is inactive.

When glucose is absent, cAMP binds to catabolite activator protein (CAP), which decreases transcription of the operon.

When tryptophan is present, it binds to the regulatory protein, activating it.

When lactose (and, therefore, allolactose) is absent, the regulatory protein is active.

When glucose is absent, cAMP binds to catabolite activator protein (CAP), activating CAP to decrease transcription of the operon.

When glucose is absent, cAMP binds to catabolite activator protein (CAP), activating CAP to increase transcription of the operon.

The lac operon undergoes negative control.

When lactose (and, therefore, allolactose) is absent, the regulatory protein is inactive.

The lac operon undergoes positive control.



Correct

The trp operon is regulated through negative control only. When tryptophan is present, the operon genes are not transcribed.

The lac operon is regulated through both negative control and positive control.

Negative control:

When lactose is absent, the repressor protein is active, and transcription is turned off.When lactose is present, the repressor protein is inactivated, and transcription is turned on.

Positive control:

When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rateof transcription if lactose is present.

Part C - Regulation of a hypothetical operon

You are studying a bacterium that utilizes a sugar called athelose. This sugar can be used as an energy source when necessary.Metabolism of athelose is controlled by the ath operon. The genes of the ath operon code for the enzymes necessary to use athelose as an energysource.

You have found the following:

The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high.When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible.The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon.

Based on this information, how is the ath operon most likely controlled?

Drag the labels onto the diagram to identify the small molecules and the states of the regulatory proteins. Not all labels will be used.

Hint 1. What terms describe operon control?

Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used.

ANSWER:



Hint 2. How is the ath operon controlled?

How do the various small molecules interact with regulatory protein(s) of the ath operon to regulate its expression?

You have found the following:

The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high.When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible.The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon.

Sort the small molecules into the appropriate bins depending on their direct effect on ath operon transcription.

ANSWER:

ANSWER:



Correct

Metabolism of the sugar athelose in this hypothetical system is controlled by an operon that exhibits both positive control and negative control.Transcription of the ath operon is turned on when athelose is present (negative control), and sped up when the bacterium runs out of glucose andmust rely on athelose for energy (positive control).

Regulation of Gene Expression in Eukaryotes

In all organisms, certain genes are expressed at any given time while other genes are not. Both prokaryotes and eukaryotes regulate gene expression atthe transcription stage. However, the greater complexity of eukaryotic cells makes it possible for gene expression to be regulated at many other stages aswell. The diagram below shows different stages at which gene expression may be regulated in eukaryotes.

Part A - Modification of chromatin structure

Which statements about the modification of chromatin structure in eukaryotes are true?

Select all that apply.

Hint 1. Chromatin structure

Eukaryotic DNA is packaged with proteins in a complex known as chromatin. Most of the proteins in chromatin are called histones. Theattraction between DNA and histones is partially due to the charges of the molecules: DNA is negatively charged, whereas histones arepositively charged because they contain positively charged amino acid residues, such as lysine.The basic structural unit of chromatin is the nucleosome, which consists of DNA wound twice around a cluster of eight histones. The amino



end, or tail, of each histone extends from the nucleosome.

Chromatin may exist in either a condensed or a decondensed form, as shown below. Chemical modifications of the chromatin determine whichform it has.

Hint 2. Do you understand acetylation and methylation of histones?

Sort the following phrases based on whether they pertain to acetylation of histone tails, methylation of histone tails, or both.

Drag each phrase to the appropriate bin.

ANSWER:

Hint 3. Epigenetic inheritance

Epigenetic inheritance is the inheritance of traits transmitted by mechanisms that do not directly involve differences in the genome sequence.Chromatin modifications, such as acetylation and methylation of histone tails, may be passed on to future generations of cells. Whereasmutations in the nucleotide sequence of DNA are permanent, modifications to chromatin structure may be reversed.

ANSWER:

Some forms of chromatin modification can be passed on to future generations of cells.

DNA is not transcribed when chromatin is packaged tightly in a condensed form.

Acetylation of histone tails in chromatin allows access to DNA for transcription.

Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA.

Methylation of histone tails in chromatin can promote condensation of the chromatin.

Acetylation of histone tails is a reversible process.



Correct

One of the mechanisms by which eukaryotes regulate gene expression is through modifications to chromatin structure. When chromatin iscondensed, DNA is not accessible for transcription. Acetylation of histone tails reduces the attraction between neighboring nucleosomes, causingchromatin to assume a looser structure and allowing access to the DNA for transcription. If the histone tails undergo deacetylation, chromatin canrecondense, once again making DNA inaccessible for transcription.

Recent evidence suggests that methylation of histone tails can promote either the condensation or the decondensation of chromatin, dependingon where the methyl groups are located on the histones. Thus, methylation can either inactivate or activate transcription, and demethylation canreverse the effect of methylation.

Changes in chromatin structure may be passed on to future generations of cells in a type of inheritance called epigenetic inheritance.

Part B - Regulation of transcription initiation

The diagram below shows two stretches of DNA in the genome of an imaginary eukaryotic cell. The top stretch of DNA includes the fantasin gene,along with its promoter and one of its enhancers. The bottom stretch of DNA includes the imaginin gene, its promoter, and one of its enhancers. Theslash marks (//) indicate that more than 1,000 nucleotides separate the promoter and enhancer of each gene.

Which statements about the regulation of transcription initiation in these genes are true?


Hint 1. Can you define terms related to transcription initiation?


ANSWER:



Hint 2. Activators and repressors

Specific transcription factors are proteins that either promote or inhibit the transcription of particular genes. Those that promote transcription arecalled activators. Many activators work by interacting with a specific distal control element and with one or more other proteins involved intranscription. These interactions are required for particular genes to be transcribed at high levels.

Specific transcription factors that inhibit transcription are called repressors. Many repressors work by preventing activators from interacting withcontrol elements or with other proteins.

ANSWER:

Correct

Only certain genes are transcribed in a eukaryotic cell at any particular time. The regulation of transcription initiation depends on the interaction ofspecific transcription factors with specific control elements in enhancers.In the imaginary eukaryotic cell used as an example here, the enhancers for the fantasin gene and imaginin gene are unique because theycontain different sets of control elements (A, B, and C for the fantasin gene; C, D, and E for the imaginin gene). Each gene will be transcribed at ahigh level when activators specific for all of the control elements in its enhancer are present in the cell.

Control elements C, D, and E are distal control elements for the imaginin gene.

The fantasin gene will be transcribed at a high level when activators specific for control elements A, B, and C are present in the cell.

Control elements A, B, and C are proximal control elements for the fantasin gene.

The imaginin gene will be transcribed at a high level when repressors specific for the imaginin gene are present in the cell.

The fantasin gene and the imaginin gene have identical enhancers.

Both the fantasin gene and the imaginin gene will be transcribed at high levels when activators specific for control elements A, B, C, D, andE are present in the cell.

Both the fantasin gene and the imaginin gene will be transcribed at high levels whenever general transcription factors are present in the cell.



Part C - Alternative RNA splicing

The diagram below shows a segment of DNA containing an imaginary gene (Z) and the primary RNA transcript that results from the transcription ofgene Z. Exons are represented in green and introns are represented in blue.

Which of the following choices represent mRNA molecules that could be produced from the primary RNA transcript by alternative RNA splicing? (Ineach choice, the yellow part on the left represents the 5' cap, and the yellow part on the right represents the poly-A tail.)


Hint 1. Exons and introns

Eukaryotic genes are composed of regions called exons and introns. Exons are regions of a gene that can be expressed because they can bepart of a final mRNA molecule. Introns are intervening regions of a gene that are not expressed because they are never part of a final mRNAmolecule.

A cell can produce different final mRNA molecules from the same gene by controlling which of the genes exons are included in each mRNAmolecule.

Hint 2. Can you describe the process of alternative RNA splicing?

Which choice(s) accurately describe(s) the process of alternative RNA splicing?


ANSWER:

ANSWER:

Correct

Alternative RNA splicing produces different mRNA molecules from the same primary RNA transcript. During alternative RNA splicing, all intronsare removed, and some exons may also be removed. The removal of different exons produces different mRNA molecules, which are thentranslated into different proteins. Alternative RNA splicing can greatly expand the number of proteins produced from the same gene.

All introns of the primary RNA transcript are removed.

Some exons of the primary RNA transcript may be removed.

All exons of the primary RNA transcript are removed.

Some introns of the primary RNA transcript are removed.



Activity: Control of Transcription

Click here to complete this activity.

Then answer the questions.

Part A

_____ bind(s) to DNA enhancer regions.

ANSWER:

Correct

Activators are a type of transcription factor that bind to enhancer regions.

Part B

What is the event that IMMEDIATELY follows the last event of this animation?To view the animation, click here. Then click on the image to start the animation.

ANSWER:

Correct

The bending of the DNA allows for the interaction of transcription factors and RNA polymerase.

Part C

Which of these indicates an enhancer region?

ANSWER:

RNA polymerase

Promoters

Introns

Activators

Exons

unbending of the DNA and the release of RNA polymerase from the promoter

binding of the activators to enhancers

transcription

binding of mRNA to the smaller ribosomal subunit

binding of RNA polymerase to the promoter



Correct

This is an enhancer region.

Part D

Which of these directly bind(s) to the promoter?

ANSWER:

Correct

Both RNA polymerase and transcription factors bind with the promoter.

Activity: Overview: Control of Gene Expression



Part A

The process of transcription is indicated by the letter _____.

A

B

C

D

C and D

A

B

C

D

C and D



ANSWER:

Correct

Transcription is the process by which information encoded in DNA is converted to information encoded in RNA.

Part B

The letter E is indicating a process of gene expression that involves _____.

ANSWER:

Correct

This is the process indicated by the letter E.

Part C

RNA processing is indicated by the letter _____.

ANSWER:

A

B

C

D

E

transcription

breakdown of mRNA

translation of mRNA

protein breakdown

unpacking of DNA



Correct

As you can see, introns have been removed and a cap and a tail added to the RNA molecule.

Part D

Which of the following processes is NOT indicated by the label A, B, C, D, or E?

ANSWER:

Correct

This process is indicated by the arrow that precedes arrow A.

Chapter 18 Pre-Test Question 5

Part A

miRNAs can control gene expression by what action?

Hint 1.

At what step in gene expression do miRNAs act?

ANSWER:

Correct

miRNAs can effectively "silence" genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable tophysically interact with the ribosomes to complete translation.

A

B

C

D

E

translation

RNA transcription

export of mRNA

DNA unpacking

RNA processing

binding to DNA and preventing transcription of certain genes

binding to mRNAs and degrading them or blocking their translation

inhibiting the catalytic activity of rRNA

seeking out viral DNA and destroying it

degrading proteins as soon as they are formed



Chapter 18 Question 27

Part A

The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA iscalled

ANSWER:

Correct


Part A

Among the newly discovered small noncoding RNAs, one type reestablishes methylation patterns during gamete formation and blocks expression ofsome transposons. These are known as

ANSWER:

Correct


Part A

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

Hint 1.

Consider which of these would promote unregulated cell division.

ANSWER:

RNA interference.

RNA targeting.

RNA disposal.

RNA blocking.

RNA obstruction.

miRNA.

snRNA.

RNAi.

siRNA.

piRNA.

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

hyperactivity of a proto-oncogene and activation of a tumor-suppressor gene

failure of a proto-oncogene to produce a protein and amplification of a tumor-suppressor gene

failure of both a proto-oncogene and a tumor-suppressor gene to produce proteins

hyperactivity of both a proto-oncogene and a tumor-suppressor gene



Correct

Excess copies of the proto-oncogene could stimulate cell division abnormally, and the inactivation of a tumor-suppressor gene would eliminate abrake on cell division.


Part A

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then

ANSWER:

Correct

Misconception Question 86

Part A

Which statement(s) about inducible operons is/are correct?


ANSWER:

Correct

An inducible operon is usually off but can be turned on when an inducer interacts with and inactivates the repressor. The enzymes in an inducibleoperon generally function in catabolic pathways. Read about inducible operons.


Part A

Which statement(s) about repressible operons is/are correct?


ANSWER:

Correct

A repressible operon is usually on but can be turned off when a corepressor interacts with and activates the repressor. The enzymes in aninducible operon generally function in anabolic pathways. Read about repressible operons.

the enzymes produced are called inducible enzymes.

the amino acid acts as a corepressor.

the amino acid turns on transcription of the operon.

the repressor is active in the absence of the amino acid.

the amino acid inactivates the repressor.

Inducible enzymes generally function in synthetic pathways that produce end products from raw materials.

In an inducible operon, the repressor is synthesized in an active form.

In an inducible operon, an inducer inactivates the repressor.

Repressible enzymes generally function in anabolic pathways.

A repressible operon is on unless a corepressor is present.

In a repressible operon, the repressor is synthesized in an active form.




Part A

A gene on human chromosome 15 is expressed throughout the body. However, in the brain, only the maternal copy of the gene is expressed, whereasthe paternal copy of the gene is silent and not transcribed. What accounts for this pattern of expression this gene displays in the brain?

ANSWER:

Correct

Imprinting of the paternal copy of the gene by DNA methylation inactivates it and prevents its expression in brain cells. Read about DNAmethylation and genomic imprinting.


Part A

Which noncoding RNAs are correctly matched with their function?


ANSWER:

Correct

Read about the multiple roles of noncoding RNAs.


Part A

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

Hint 1.

Is it normally on or normally off?

ANSWER:

Correct

The lac repressor keeps the production of lactose-digesting enzymes turned off. When allolactose is present, the lac repressor is inactivated,allowing the expression of lactose-digesting enzymes.

In the brain, the maternal copy of the gene is methylated whereas the paternal copy is un-methylated.

The copies of this gene in brain cells are coordinately controlled with the copies of the gene in body cells.

Through genomic imprinting, methylation regulates expression of the paternal copy of the gene in the brain.

MicroRNAs (miRNAs) bind to complementary sequences in mRNA and block its translation.

Piwi-associated RNAs (piRNAs) reestablish appropriate methylation patterns in the genome during gamete formation.

Small interfering RNAs (siRNAs) bind to complementary sequences in mRNA and block its translation.

When activated, the lac operon induces the production of lactose-digesting enzymes.

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

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

When allolactose is present, it induces repression of gene expression.

When activated, the lac operon induces repression of gene expression.




Part A

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

Hint 1.

DNA methylation accounts for genomic imprinting.

ANSWER:

Correct

DNA methylation, involving the attachment of methyl groups to certain bases, is a mechanism for the long-term inactivation of genes duringdevelopment.


Part A

Which of the following mechanisms is (are) used to coordinate the expression of multiple, related genes in eukaryotic cells?

ANSWER:

Correct


Part A

Two potential devices that eukaryotic cells use to regulate transcription are

ANSWER:

Correct

increase the rate of transcription

cause apoptosis

facilitate the binding of DNA to intermediate filaments

inactivate genes

terminate transcription

A specific combination of control elements in each genes enhancer coordinates the simultaneous activation of the genes.

A single repressor is able to turn off several related genes.

The genes share a single common enhancer, which allows appropriate activators to turn on their transcription at the same time.

Environmental signals enter the cell and bind directly to promoters.

The genes are organized into large operons, allowing them to be transcribed as a single unit.

histone amplification and DNA acetylation.

DNA methylation and histone modification.

DNA acetylation and methylation.

DNA methylation and histone amplification.

DNA amplification and histone methylation.




Part A

You are given an experimental problem involving control of a gene's expression in the embryo of a particular species. One of your first questions iswhether the gene's expression is controlled at the level of transcription or translation. Which of the following might best give you an answer?

ANSWER:

Correct


Part A

The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?

Hint 1.

Review the structure of a virus.

ANSWER:

Correct

The protein shell that encloses a viral genome is a capsid.

Viral Replication

Viruses are nonliving intracellular parasites that infect plants, animals, and bacteria. Viruses use host cell components to make copies of themselves.Often, but not always, the process of viral replication kills the host cell.

Part A - Virus structure

Sort the items according to whether they may be found only in free virus particles, only in uninfected host cells, or in both viruses and host cells.

Drag each item to the appropriate bin.

Hint 1. Viruses and host cells

Viruses are obligate intracellular parasites: They can reproduce within a host cell but cannot reproduce on their own. Although a few viruses caninfect a variety of species, many viruses are able to infect only one particular species. Host specificity typically results from the virussrecognition of certain proteins or glycoproteins on the surface of host cells.Once inside a cell, the virus takes over the cell, reprogramming it to manufacture viral proteins and duplicate viral nucleic acids. The host celldoes this using its own components (nucleosides, ribosomes, tRNA, etc.) and usually dies after releasing a new generation of viruses, whichcan go on to infect other cells.

An analysis of amino acid production by the cell shows you that there is an increase at this stage of embryonic life.

You measure the quantity of the appropriate pre-mRNA in various cell types and find they are all the same.

You use an antibiotic known to prevent translation.

You explore whether there has been alternative splicing by examining amino acid sequences of very similar proteins.

You assess the position and sequence of the promoter and enhancer for this gene.

envelope

capsid

nuclear envelope

nucleoid

genome



Hint 2. What are the parts of a virus?


ANSWER:

ANSWER:



Correct

Viruses are infectious particles that contain genetic material (either DNA or RNA) surrounded by a capsid (protein shell). Some viruses also havea membranous envelope that contains glycoproteins.

Part B - Reproductive cycles of a bacteriophage

Classify each phrase as applying to the lytic cycle, the lysogenic cycle, or both types of reproductive cycles of phages.

Drag the descriptions into the appropriate bins.

Hint 1. Bacteriophages

Bacteriophages (literally "bacteria-eaters") are viruses that infect bacteria. Bacteriophages contain double-stranded DNA and can duplicatethemselves by two alternative mechanisms: the lytic cycle and the lysogenic cycle.

Hint 2. Lytic cycle

In the lytic cycle, the bacteriophage binds to the surface of the bacterium. The virus then injects its own DNA into the cell, and the cell's DNA isbroken up (hydrolyzed).The viral DNA directs the replication of viral DNA and the synthesis of viral proteins, which self-assemble into new viruses. Finally, the virustriggers destruction of the bacterial cell wall, which causes the cell to lyse, releasing new viruses that can go on to infect other cells.

Hint 3. Lysogenic cycle

Unlike the lytic cycle, the lysogenic cycle does not lyse the host cell. After the bacteriophage attacks the cell, the viral DNA is integrated intothe bacterial chromosome and is duplicated with each cell division. In this manner, a large number of infected bacteria form.Occasionally, an infected bacterium in the lysogenic cycle can enter the lytic cycle, in which viral particles are produced and the cell iseventually ruptured.

Hint 4. What are the differences between the lytic and lysogenic cycles?

Label the diagram of the lytic and lysogenic cycles.

Drag the labels to their appropriate locations on the diagram of the cycle.

ANSWER:



ANSWER:



Correct

Bacteriophages, which contain double-stranded DNA, can reproduce by two alternative mechanisms: the lytic cycle and the lysogenic cycle.

In the lytic cycle, virus parts are made, new viruses are assembled, and the cell is lysed, releasing the newly assembled viruses.In the lysogenic cycle, the viral DNA incorporates into the bacterial DNA and is passed on to daughter bacterial cells when theinfected bacteria reproduce normally.

Occasionally, an infected bacterium in the lysogenic cycle can enter the lytic cycle, in which viral particles are produced and the cell is eventuallyruptured.

Part C - Virus properties

Which statements about viruses are true?

Select the four statements that are true.

Hint 1. Enveloped viruses and nonenveloped viruses

In an enveloped virus, the capsid is surrounded by a membrane called the envelope. If the envelope fuses with a host cells plasma membrane,the capsid and viral genome can enter the cell. When an enveloped virus emerges from an infected cell, it takes a small amount of cellmembrane with it (in the form of the viral envelope).In a nonenveloped virus, the capsid does not have a surrounding membrane.

Hint 2. Reproductive cycle of a retrovirus

A retrovirus is an enveloped virus that carries single-stranded RNA. In the host cell, a viral enzyme called reverse transcriptase synthesizes aDNA strand complementary to the viral RNA. The newly formed DNA goes on to make copies of the virus.

Hint 3. HIV

Human immunodeficiency virus (HIV) is a retrovirus that contains two copies of its RNA genome and two copies of reverse transcriptase in acapsid. The viral envelope facilitates binding to a white blood cell. After the virus enters the host cell, the capsid releases the RNA and reversetranscriptase.

Hint 4. What is the diversity of viral genetic material?

What genetic material has not been found in any virus?

ANSWER:

single-stranded DNA

double-stranded DNA

single-stranded RNA

double-stranded RNA

a combination of DNA and RNA (single- or double-stranded)



ANSWER:

Correct

Viruses are classified into two major groups: nonenveloped and enveloped.

Nonenveloped viruses (a) typically exit the host cell by bursting through the plasma membrane.Enveloped viruses (b) generally escape from the host cell by budding. Because of this, the viral envelope is often derived from thehost cell's plasma membrane.

Viruses contain either single-stranded DNA, double-stranded DNA, single-stranded RNA, or double-stranded RNA. Human immunodeficiency virus(HIV) is a retrovirus that contains two copies of its RNA genome and two copies of reverse transcriptase. The HIV viral envelope facilitates bindingto a white blood cell. After HIV enters the cell, the reverse transcriptase synthesizes viral DNA from viral RNA.

Activity: Phage Lysogenic and Lytic Cycles



Part A

A retrovirus contains RNA.

All viral genomes contain both DNA and RNA.

HIV contains two identical strands of DNA.

All RNA-containing viruses are retroviruses.

The capsid enters the host cell if the virus is enveloped.

HIV contains reverse transcriptase.

Enveloped viruses bud from the host cell.



Click on the diagram to start the animation. The arrow is indicating _____.

ANSWER:

Correct

Viral DNA incorporated into host DNA is referred to as a "prophage."

Part B

Click on the diagram to start the animation. This animation is illustrating an early stage of _____.

ANSWER:

Correct

Integration of viral DNA into host DNA is an early stage of the lysogenic cycle.

Part C

In the lysogenic cycle _____.

ANSWER:

Correct

Viral DNA, incorporated into host DNA as a prophage, is replicated along with host DNA.

Part D

Click on the diagram to start the animation. Which of these is the best description of this animation?

host cell DNA

a capsid

an envelope

a Golgi apparatus

a prophage

the lytic cycle

the lysogenic cycle

transcription

translation

lysis

host DNA is destroyed and viral DNA is replicated

a bacterium replicates without passing viral DNA to its daughter cells

viral DNA is destroyed and host DNA is replicated

a bacterium divides once before the lytic cycle is initiated

viral DNA is replicated along with host DNA



ANSWER:

Correct

Phage DNA has exited the bacterial chromosome as a prelude to taking over the host's metabolic machinery.

Part E

Cycle A is the _____ cycle and cycle B is the _____ cycle.

ANSWER:

Correct

The lytic cycle concludes with rupture of the host cell. The lysogenic cycle involves replication of viral DNA along with replication of the host.

Activity: Retrovirus (HIV) Reproductive Cycle



Part A

The genetic material of HIV consists of _____.

The lysogenic cycle has begun.

The lytic cycle is making a transition to the lysogenic cycle.

The bacterium has successfully fought off the viral infection.

The lysogenic cycle is making a transition to the lytic cycle.

The host cell has begun to reproduce.

lytic ... lysogenic

lytic ... phage

lysogenic ... phage

lysogenic ... lytic

phage ... lysogenic



ANSWER:

Correct

The genetic material of HIV consists of two molecules of single-stranded RNA.

Part B

Which of these binds to receptor molecules on the host cell membrane?

ANSWER:

Correct

Glycoproteins on the viral envelope recognize and bind to receptors on the host cell.

Part C

What is the function of reverse transcriptase?

ANSWER:

Correct

This is the function of reverse transcriptase.

Part D

What is the source of a viral envelope?

ANSWER:

single-stranded DNA

single-stranded RNA

double-stranded DNA

double-stranded RNA

none of the above

A

B

C

D

E

It catalyzes the formation of a polypeptide from an RNA template.

It catalyzes the formation of DNA from a polypeptide template.

It catalyzes the formation of RNA from a polypeptide template.

It catalyzes the formation of RNA from a DNA template.

It catalyzes the formation of DNA from an RNA template.



Correct

The viral envelope is derived from host cell membrane.

Part E

Which of these is reverse transcriptase?

ANSWER:

Correct

This is reverse transcriptase.

Part F

Which of these is the viral genome?

ANSWER:

Correct

HIV is an RNA virus.

host cell DNA

prophages

provirus

host cell membrane

viral glycoproteins

A

B

C

D

E

A

B

C

D

E



Part G

To view the animation, click here. Then click on the image to start the animation.

Click on the diagram to start the animation. What enzyme is responsible for the process seen here?

ANSWER:

Correct

Reverse transcriptase catalyzes the formation of DNA from an RNA template.

Part H

Double-stranded viral DNA is incorporated into a host cell as a _____.

ANSWER:

Correct

"Provirus" is the name given to double-stranded viral DNA that has been incorporated into a host cell's genome.


Part A

Identify all correct statements about how viroids differ from viruses.


ANSWER:

Correct

Unlike viruses, viroids do not encode proteins but can replicate in host plant cells, apparently using host cell enzymes. Read about viroids.


Part A

How do prions differ from viruses?


ANSWER:

RNA polymerase

DNA polymerase

reverse transcriptase

endonuclease

DNA ligase

promoter

provirus

transposon

lac

homeoboxes

Unlike viruses, viroids cause plant disease.

Unlike viruses, viroids do not encode proteins.

Unlike viruses, the genetic material of a viroid is protein.



Correct

Read about prions.

Score Summary:

Your score on this assignment is 99.6%.You received 23.91 out of a possible total of 24 points.

Unlike viruses, prions do not include any nucleic acids.

Unlike a virus, a prion is a single molecule.

Unlike viruses, prions are infectious proteins.

Gene Regulation

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Transcript of Gene Regulation