Question 1

If you were able to look very closely at a portion of DNA and find methylated histones,you would

Accepted Answer

Methylated histones are associated with inactive chromatin. This is because the addition of methyl groups to histones can cause them to condense, resulting in a tighter packing of the DNA and a less accessible state for gene expression. Therefore, if methylated histones were observed in a portion of DNA, it would suggest that the region is in an inactive state.

Question 2

Although the specific mechanism of RNA interference has not been fully defined,it involves

Accepted Answer

RNA interference (RNAi) involves double stranded RNA interfering with mRNA. This double stranded RNA can be naturally occurring in the cell or introduced through experimental techniques. The double stranded RNA is processed into small interfering RNAs (siRNAs) that target complementary mRNA molecules for degradation or translational repression. This process can regulate gene expression and is used as a research tool to study gene function.

Question 3

What is the difference between a gene that is derepressed and one that is induced?

Accepted Answer

A derepressed gene is turned on because a repressor protein is not bound without its cofactor. An induced gene is turned on because an inducer molecule prevents binding of the repressor. Therefore, derepression and induction are different mechanisms of turning on a gene.

Question 4

Vertebrate cells possess a protein that binds to clusters of 5-methylcytosine and ensures the gene will stay in the "off" position.This control of gene regulation is a result of

Accepted Answer

The protein that binds to clusters of 5-methylcytosine is called a methyl-CpG binding protein, which specifically recognizes and binds to methylated cytosines. Methylation is a key epigenetic modification that can regulate gene expression by either inhibiting or promoting transcription. In this case, the binding of methyl-CpG binding protein to methylated regions in DNA ensures that the associated gene will remain in the "off" position by preventing transcription factors from binding to the DNA and initiating transcription.

Question 5

Elucidation of the histone code might

Accepted Answer

The histone code hypothesis suggests that specific combinations of histone modifications can regulate gene expression by turning genes on or off.

Question 6

Production of the iron-storing protein ferritin is regulated by aconitase,which binds to a 30-nucleotide sequence at the beginning of the ferritin mRNA and interferes with ribosome binding.Aconitase must be a

Accepted Answer

Aconitase interferes with ribosome binding, indicating that it affects translation rather than transcription. Therefore, it must be a translation repressor protein.

Question 7

The p300/CBP (CREB-binding protein)proteins are histone acetyltransferases that help regulate the transcription of many genes.Based on this information you can conclude that these proteins

Accepted Answer

The statement directly mentions that these proteins help regulate gene transcription by acetylating histones, which is a key step in chromatin remodeling. Therefore, the most appropriate choice is B), remodeling chromatin. The other choices are not mentioned in the statement and are not likely based on the given information.

Question 8

You are studying the function of a recently identified gene in C.elegans.You perform genetic screens for several months in an attempt to isolate loss-of-function gene mutations,but your efforts are unsuccessful.Your advisor suggests you try another approach to eliminate gene function.The best technique to accomplish this goal would be

Accepted Answer

RNA interference (RNAi) is a technique used to silence gene expression through the degradation of mRNA. By specifically targeting the mRNA of the gene of interest, RNAi can effectively knock down its expression, allowing for the study of its function. This would be the most appropriate technique to eliminate the function of the gene in question, as the genetic screens for loss-of-function mutations were unsuccessful.

Question 9

Within its core a nucleosome contains ________ histones.

Accepted Answer

Within its core, a nucleosome contains eight histones. These histones are arranged in two copies each of histones H2A, H2B, H3, and H4, forming an octamer core around which DNA is wrapped.

Question 10

The gene encoding apolipoprotein B exists in two isoforms,APOB100 and APOB48.These two forms are produced as a result of

Accepted Answer

APOB100 and APOB48 are produced from the same gene through a process called RNA editing. In this process, a specific cytidine nucleotide in the APOB mRNA is deaminated to uridine, creating a stop codon that results in the shorter APOB48 isoform. This editing occurs in the intestine, leading to the production of APOB48, while the liver produces the full-length APOB100.

Question 11

DNA methylation is the only known natural modification of DNA.It affects

Accepted Answer

DNA methylation affects cytosine bases where a methyl group is added to the fifth carbon of the cytosine ring. This modification regulates gene expression and plays a role in processes such as embryonic development, X-chromosome inactivation, and genomic imprinting. There is no known natural modification of adenine, guanine or thymine bases in DNA.

Question 12

You work for a pharmaceutical company that designs small RNAs,used to control expression of disease genes.The primary focus area of your research should be

Accepted Answer

Small RNAs, such as siRNAs and miRNAs, primarily function to repress translation by binding to target mRNA, preventing protein synthesis and thus controlling gene expression.

Question 13

The enzyme dicer chops dsRNA molecules into small pieces of

Accepted Answer

Dicer chops double-stranded RNA (dsRNA) molecules into small pieces of microRNA (miRNA) and small interfering RNA (siRNA). Therefore, the best choice is B, which includes both miRNA and siRNA.

Question 14

In vertebrates,DNA methylation - the addition of a methyl group to DNA nucleotides - ensures that

Accepted Answer

DNA methylation plays a crucial role in regulating gene expression. Once a gene is methylated and turned off, it will remain off as the presence of methyl groups inhibits the binding of transcription factors and other proteins necessary for gene expression. This ensures that certain genes are only expressed when needed, and helps establish cell differentiation and specialization.

Question 15

Small RNAs can regulate gene expression.One type,called micro RNA (miRNA),acts by binding directly to

Accepted Answer

Micro RNA (miRNA) acts by binding directly to mRNA to prevent translation, not transcription or binding to tRNA.

Question 16

You are studying the effects of specific transcription factors on the activation of gene expression.You notice that one particular transcription factor binds far away from the promoter of its target gene.What can explain this?

Accepted Answer

DNA looping brings the transcription factor closer to the promoter and initiates gene transcription.

Question 17

The primary transcripts in eukaryotes are most accurately described as

Accepted Answer

Primary transcripts, also known as pre-mRNA, are the initial RNA copies of the entire gene including both exons and introns. They are transcribed by RNA polymerase and require further processing to remove introns and join exons together in order to become functional mRNA molecules.

Question 18

Eukaryotic cell mRNA transcripts can remain in the cell for hours because they are

Accepted Answer

Eukaryotic cell mRNA transcripts are stable because they undergo post-transcriptional modifications that protect them from degradation. These modifications include the addition of a 5' cap and a poly(A) tail, which help stabilize the transcript and prevent degradation by exonucleases. This stability allows the mRNA to remain in the cell for hours and be used for protein synthesis.

Question 19

Histones that are tightly wound by DNA and are the basic unit of chromatin are called

Accepted Answer

Histones that are tightly wound by DNA and are the basic unit of chromatin are called nucleosomes.

Question 20

You are working to identify enhancer regions of a particular gene.The best place to look is

Accepted Answer

Enhancer regions can be located upstream of the promoter, sometimes at a considerable distance away, and can even be found within introns. They work by interacting with the promoter region to increase transcriptional activity, so looking upstream of the promoter is the best place to start. Downstream regions and exons are involved in other processes, such as splicing and mRNA stability, and are less likely to contain enhancer elements.

Quiz 16: Control of Gene Expression