Question 1

A histone code is the:

Accepted Answer

A histone code refers to the pattern of chemical modifications, such as acetylation or methylation, on the tails of the histone proteins. These modifications can affect the structure of the chromatin and regulate gene expression.

Question 2

Which of the following processes produce different proteins in different cells from the same primary transcript?

Accepted Answer

D, E

Question 3

A researcher notices that women working in the petrochemical industry who are exposed to aromatic hydrocarbons may have a greater incidence of breast cancer than women without such exposure. The researcher undertakes a study of the BRCA1 promoter using the restriction enzymes MspI and HpaII. MspI cleaves double-stranded DNA at 5'-CCGG-3' regardless of whether the CG in the middle has cytosine methylation, whereas HpaII cleaves double-stranded DNA at 5'-CCGG-3' only when the CG in the middle lacks cytosine methylation. For a region of double-stranded DNA in the promoter region of BRCA1, tumor cells from the breasts of exposed women with breast cancer and nontumor cells from breasts from the same women show the illustrated patterns of bands produced by MspI and HpaII:  Which of the following statements are supported by this evidence?

Accepted Answer

A, E

Question 4

Transcription of a gene can be increased or decreased according to the:

Accepted Answer

The combination of amino acid modifications in the histone tails can affect the accessibility of the DNA to transcription factors and RNA polymerase, thus increasing or decreasing transcription of the gene. Choices A, B, and C are not directly related to gene expression regulation through histone modifications.

Question 5

_____ is defined as the process by which information from a gene is used in the synthesis of a functional gene product.

Accepted Answer

Gene expression is the process in which information from a gene is used to synthesize a functional gene product, such as a protein or RNA molecule. This process involves the transcription of DNA to RNA and the translation of RNA to a protein or the activity of the RNA molecule itself. Gene expression is regulated by various mechanisms, including transcriptional and post-transcriptional regulation, chromatin remodeling, and epigenetic modifications.

Question 6

The methylation state of an individual CpG island:

Accepted Answer

The methylation state of an individual CpG island can change over time in response to environmental cues, allowing genes to be turned on or off as needed. This process is known as epigenetic regulation and plays a critical role in development, differentiation, and adaptation to changing environmental conditions. However, it should be noted that not all CpG islands are equally susceptible to epigenetic changes and some may be more stable or resistant to modification.

Question 7

Chromatin remodeling refers to the process by which:

Accepted Answer

Chromatin remodeling involves the repositioning of nucleosomes to expose different stretches of DNA to the nuclear environment, which can affect gene expression. This can involve changes in the acetylation or methylation of histone proteins, as well as the activity of ATP-dependent chromatin remodeling complexes. Choices B and C describe steps in transcription initiation, but do not accurately describe chromatin remodeling. Choice D refers to a specific type of DNA modification that can affect chromatin structure, but is not the same as chromatin remodeling. Choice E is incorrect, as mutations can affect DNA structure, but they do not necessarily involve chromatin remodeling.

Question 8

In the hierarchy of levels of gene regulation, in what order do the following levels of regulation take place? (1) post-translational modification
(2) RNA processing
(3) transcription
(4) chromatin remodeling

Accepted Answer

Chromatin remodeling occurs first in the hierarchy of levels of gene regulation, as it involves changing the accessibility of DNA to transcription factors and other regulatory proteins. Transcription occurs after chromatin remodeling, allowing for the synthesis of RNA. RNA processing, which includes splicing and other modifications, occurs after transcription. Finally, post-translational modification occurs after the RNA is translated into protein. Therefore, the correct order is (4)-(3)-(2)-(1).

Question 9

X-inactivation is caused by the accumulation of:

Accepted Answer

X-inactivation is indeed caused by noncoding RNA produced by the Xist gene, which coats the X chromosome and induces changes such as DNA methylation and histone modification, effectively silencing transcription from that chromosome.

Question 10

Which process produces multiple proteins from the same primary transcript in the same cell?

Accepted Answer

The answer of Which process produces multiple proteins from the...

Question 11

In humans and other mammals, X-inactivation takes place:

Accepted Answer

X-inactivation takes place early in development, with each new cell inheriting the same inactivated X chromosome as its parent cell. This process ensures that female mammals, who have two X chromosomes, do not produce twice as many X chromosome gene products as male mammals, who only have one X chromosome.

Question 12

A CpG island is:

Accepted Answer

A CpG island is a sequence of DNA with a high frequency of cytosine-guanine (CpG) dinucleotides. These regions occur predominantly in or near the promoter regions of genes, where they often play a crucial role in regulating gene expression. Furthermore, methylation of CpG islands is associated with transcriptional silencing, and changes in the methylation status of CpG islands may contribute to the development of various diseases.

Question 13

The diagram shown here is part of an RNA transcript containing four open reading frames (M, H, K, and L) and three introns (1, 2, 3). The sites labeled d1-d3 are nucleotides immediately before each intron on the 5' side and those labeled a1-a3 are nucleotides immediately after each intron on the 3' side. Splicing out an intron involves cleaving the DNA at the d and a sites at either end of the intron.  A missense mutation takes place in open reading frame K. In which possible alternative splice forms of the transcript would the missense mutation not affect the polypeptide product?

Accepted Answer

The answer of The diagram shown here is part of...

Question 14

The diagram shown here is part of an RNA transcript containing four open reading frames (M, H, K, and L) and three introns (1, 2, 3). The sites labeled d1-d3 are nucleotides immediately before each intron on the 5' side and those labeled a1-a3 are nucleotides immediately after each intron on the 3' side. Splicing out an intron involves a spliceosome facilitating the cleavage of the DNA at the d and a sites at either end of the intron.  A missense mutation takes place in open reading frame H. In which possible alternative splice forms of the transcript would the missense mutation not affect the polypeptide product?

Accepted Answer

The answer of The diagram shown here is part of...

Question 15

Modifications of histone tails can:

Accepted Answer

Modifications of histone tails can affect chromatin structure, activate transcription of some genes, repress transcription of some genes, and affect expression of some genes in response to the environment. Therefore, all of the given choices are correct.

Question 16

Sex-specific silencing of gene expression is known as:

Accepted Answer

X-inactivation is the process by which one of the X chromosomes in females is inactivated to compensate for the double dose of X-linked genes present in females compared to males. This silencing of one of the X chromosomes is an example of sex-specific gene expression regulation.

Question 17

In mammals, dosage compensation refers to a mechanism in which:

Accepted Answer

In mammals, dosage compensation refers to the mechanism by which X chromosome genes are regulated differently in males and females because members of one sex (females) have two X chromosomes, whereas members of the other sex (males) have only one. This allows for equal expression of X-linked genes between the sexes.

Question 18

In general, when cytosine bases in CpG islands are methylated:

Accepted Answer

Methylation of cytosine bases in CpG islands is a mechanism for gene silencing or transcriptional repression. When this occurs, the enzyme methyltransferase adds a methyl group to the cytosine, and transcription factors are unable to bind to the DNA, resulting in less gene expression or transcription. Therefore, the correct answer is C) transcription is repressed.

Question 19

The diagram shown here is part of an RNA transcript containing four open reading frames (M, H, K, and L) and three introns (1, 2, 3). The sites labeled d1-d3 are nucleotides immediately before each intron on the 5' side and those labeled a1-a3 are nucleotides immediately after each intron on the 3' side. Splicing out an intron involves a spliceosome facilitating the cleavage of the DNA at the d and a sites at either end of the intron.  How many processed transcripts are possible in which two d sites and two a sites are cleaved?

Accepted Answer

If two d sites and two a sites are cleaved, introns 1 and 3 will be spliced out, leaving only the exon between them. The potential transcripts are:
-MHKL (no splicing)
-MH-L (splice out intron 1)
-M-KL (splice out intron 3)
-M-L (splice out introns 1 and 3)

Therefore, there are two possible processed transcripts.

Question 20

Two related but distinct neurological disorders are Prader-Willi syndrome (PWS) and Angelman syndrome (AS). Children with PWS are obese, have weak muscle tone, and delayed development. Children with AS have severe speech impairment, developmental delay, intellectual disability, and problems with movement and balance. However, both disorders are due to the deletion of the same part of chromosome 15. When the deletion is in the copy of chromosome 15 that came from the father, the child has PWS, but when the deletion is in the copy of chromosome 15 that came from the mother, the child has AS. What hypothesis can explain these observations?

Accepted Answer

Parental imprinting occurs when one copy of a gene is silenced based on its parental origin. This phenomenon explains the difference in phenotype between PWS and AS despite the same genetic deletion on chromosome 15. The genes in the deleted region on chromosome 15 are normally subject to imprinting, with the paternal copy being active and the maternal copy being silenced. In individuals with PWS, the deletion removes the active paternal genes, resulting in the manifestation of PWS symptoms. In individuals with AS, the deletion removes the silenced maternal genes, resulting in the manifestation of AS symptoms.

Quiz 19: Genetic and Epigenetic Regulation