a signal received by the cell causes the attachment of

1. The diagram below shows the arrangement of chromatin (thick black strands) around histones on

a chromosome in the nucleus of a eukaryotic cell.

A signal received by the cell causes the attachment of acetyl groups (–COCH3) to the histones,

and the chromatin-histone complex changes, as shown below.

4.7 A: Factors Affecting Eukaryotic Gene Expression Quiz

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Which statement best explains how this change will affect cellular activity?

(A) Histone acetylation will reduce gene expression, because the acetyl groups prevent RNA

polymerase from accessing the coding regions.

Distractor Rationale:

This answer suggests the student may understand that RNA polymerase is involved in

transcribing DNA into mRNA, but does not understand that histone acetylation increases

gene expression by exposing DNA in order for transcription to take place, whereas

methylation reduces gene expression by restricting access of transcription factors to DNA.

(B) Histone acetylation will reduce gene expression, because the acetyl groups will bind to

chromatin and prevent proteins from initiating transcription.


This answer suggests the student may understand that acetylation of histones plays a role in

gene expression, but does not understand that histone acetylation does not repress

genes, and that, instead, it allows for gene transcription.

(C) Histone acetylation will increase gene expression, because the chromatin is no longer tightly

bound to the histones and can be transcribed.

Rationale:

This answer suggests the student understands that histone acetylation allows for gene

expression because it “uncoils” DNA from the histone and allows genes to be exposed to

transcription factors that initiate protein synthesis.

(D) Histone acetylation will increase gene expression, because the acetyl-histone complexes

can bind to promoter regions on the chromatin and activate the transcription of genes.


This answer suggests the student may understand that gene expression can be initiated

when compounds bind to a promoter, but does not understand that acetylated histone

complexes do not regulate genes by binding to promoter regions and that acetylated

histones instead act by separating from chromatin to expose genes for transcription.

Aligned to: LO 4.7 CA 4.7: Represent Mechanisms of Specialization


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2. A methyl group (CH3) can be attached to a cytosine base on DNA, as shown in the diagram

below. When a methyl group is attached to a base, enhancers and activator proteins are unable

to access the base.

A certain gene is identified that contains many methyl groups, compared to other regions of DNA.

Which statement best explains the significance of methylation to this gene?

(A) The gene will probably not be transcribed into RNA, because transcription factors will not be

able to bind to the gene to initiate transcription.

Rationale:

This answer suggests the student understands that DNA methylation blocks gene

expression by preventing the binding of transcription factors to DNA.

(B) The gene will probably be transcribed into RNA, but not translated into a polypeptide,

because enhancers will be unable to convert the nucleic acid code into amino acids.


This answer suggests the student may understand that DNA methylation blocks gene

expression, but does not understand that this process prevents transcription because

transcription factors cannot bind to DNA to initiate transcription, and that DNA methylation is

not involved in the translation of RNA into an amino acid sequence.

(C) The gene will probably not be transcribed into mRNA, because the mRNA will have

defective cytosine nucleotides that will be unable to bind with complementary DNA

nucleotides.


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This answer suggests the student may understand that DNA methylation blocks gene

expression, but does not understand that this process prevents transcription and the

formation of mRNA because DNA methylation prevents transcription factors from binding to

DNA and does not affect RNA.

(D) The gene will probably be transcribed and translated into an amino acid sequence, but the

process will continue for a long time and produce excess polypeptides, because the mRNA

cannot be properly degraded.


This answer suggests the student may understand that methylation of certain regulatory

genes (ribonuclease) may slow the breakdown of mRNA, which would result in greater

production of polypeptides, but does not understand that the methylation of this gene

would prevent expression because transcription factors would not be able to bind to the

DNA to initiate transcription.


3. Fur coloration in Himalayan rabbits is determined by genetic and environmental factors. The

pictures below show three genetically identical rabbits reared at three different temperatures.

Which statement best explains why fur coloration in Himalayan rabbits is different at different

temperatures?

(A) Fur coloration is different because cold temperatures cause mutations in genes governing

fur color in certain parts of rabbits.


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This answer suggests the student may understand that some environmental factors can

cause genetic mutations, but does not understand that cold temperatures are not

associated with an increased risk of genetic mutation and that the differential expression of

genes in Himalayan rabbits is caused by a difference in rearing temperature, not mutations.

(B) Fur coloration is different because warm temperatures denature dark-pigmented proteins,

which results in rabbits with only white fur.


This answer suggests the student may understand that high temperatures can denature

proteins, but does not understand that this outcome is unlikely because the temperature

range affecting Himalayan rabbits is lower than the temperature needed to denature most

biological enzymes, and the temperature is instead affecting gene expression and resulting

in different phenotypes.

(C) Fur coloration is different because different temperatures cause DNA to arrange into

different sequences, and this alters the genes that express fur color in rabbits.


This answer suggests the student may understand that environmental factors such as

temperature may change gene expression, but does not understand that this explanation

is unlikely because temperature may affect gene expression, but would not affect DNA

arrangement.

(D) Fur coloration is different because different temperatures cause differential expression of

certain genes, which produces different fur colors in rabbits.

Rationale:

This answer suggests the student understands that environmental factors such as

temperature may affect gene expression and that this may result in different phenotypes.



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4. The diagram below shows a hormone initiating a change in a cell.

Based on the process illustrated in the diagram, which statement best explains how the hormone

initiates a response in the cell?

(A) The hormone initiates a response in the cell by binding to a protein receptor on RNA

polymerase, allowing the enzyme to transcribe a gene.


This answer suggests the student may understand that gene expression involves initiating

the transcription of DNA by RNA polymerase, but does not understand that the hormone

shown in the diagram does not directly initiate this because the hormone is binding to a

protein receptor, not to RNA polymerase. The protein/hormone complex then binds to a

regulatory region on the gene (DNA), which activates the gene for transcription.

(B) The hormone initiates a response in the cell by binding to a protein receptor, initiating a

series of kinase reactions that result in transcription of a gene in the nucleus.


This answer suggests the student may understand that many hormones initiate gene

expression via protein kinase reactions, but does not understand that this is not the

pathway illustrated in the diagram because there is no indication that protein kinases are

active in the process; rather, the protein/hormone complex shown in the diagram is binding

to a regulatory region on the gene (DNA), which activates the gene for transcription.


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(C) The hormone initiates a response in the cell by binding to a protein receptor, allowing the

protein/hormone complex to bind to the gene and initiate transcription.

Rationale:

This answer suggests the student understands that the hormone shown in the diagram

controls gene expression by binding to a receptor protein and allowing the protein to activate

a gene for transcription.

(D) The hormone initiates a response in the cell by binding to a protein receptor on a ribosome,

initiating transcription and translation of a gene.


This answer suggests the student may understand that hormones and ribosomes are both

involved in gene expression, but does not understand that a hormone binding to a receptor

on a ribosome is not the correct description of the pathway shown in the diagram, because

regulatory proteins interact with hormones to regulate gene expression, and ribosomes are

involved with translation of the genetic code into polypeptides.



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a signal received by the cell causes the attachment of

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