Question 1

You are treating cultured cells with an experimental compound. You find that addition of the compound results in a 2-fold increase in the expression of a specific gene. However, you find that the addition of the test compound causes a 10-fold increase in the level of the protein derived from the gene. The major effect of this experimental compound is most likely to be a decrease in which of the following?

Accepted Answer

The compound likely decreases the degradation of mRNA by nucleases, leading to more mRNA available for translation, which results in a greater increase in protein levels compared to mRNA levels.  The disconnect between the level of gene expression, which results in mRNA increases and the level of protein increases from the resultant mRNAs can be accounted for by numerous consequences. However, in this case the most likely cause of the dramatically elevated level of protein from a slight elevation in mRNA levels is increased mRNA stability. The more stable mRNA can be engaged by the translational machinery more often resulting in more protein being made. Therefore, the test compound is most likely inhibiting the degradation of mRNAs by ribonucleases.

Question 2

A transcriptional promoter is required for which of the following processes?

Accepted Answer

The transcriptional promoter is required for the initiation of RNA synthesis.  The promoter region is a specific sequence of DNA upstream of the transcription start site of a gene. Promoters stimulate the initiation of transcription. Promoters are located near the genes they transcribe, on the same strand and upstream on the DNA.

Question 3

The most common mechanism for the regulated expression of human genes during fetal development occurs at which of the following levels?

Accepted Answer

The initiation of RNA synthesis, or transcriptional regulation, is the primary mechanism for controlling gene expression during fetal development. This process determines which genes are transcribed into RNA, thus influencing the proteins that will be produced.  In eukaryotic cells, the ability to express biologically active proteins can be regulated at several different stages from the activity of the gene to the final functional protein. Transcriptional initiation is the most important mode for control of eukaryotic gene expression.

Question 4

Transcription factor proteins bind to specific DNA sequences present in their target genes. These factors subsequently lead to increased transcription of target genes by which of the following processes?

Accepted Answer

Transcription factors increase the rate of initiation by helping RNA polymerase bind to the promoter region of the gene, facilitating the start of transcription. Transcription factors are proteins that bind to specific DNA sequences, thereby controlling the activity of the gene whose regulatory sequences they bind. Transcription factors perform this function alone or with other proteins in a complex, by promoting or blocking the recruitment of RNA polymerase to specific genes. A defining feature of transcription factors is that they contain one or more DNA-binding domains (DBDs), which recognize and bind to specific sequences of DNA adjacent to the genes that they regulate.

Question 5

Which of the following mechanisms inhibits expression of imprinted genes?

Accepted Answer

Methylation of cytosine residues within the gene is a key mechanism for inhibiting the expression of imprinted genes, as it can silence gene expression by preventing transcription factor binding or recruiting proteins that compact chromatin.  Genomic imprinting refers to a genetic phenomenon whereby there is preferential expression of a gene from only 1 of the 2 parental alleles. This phenomenon of allele-specific expression results from allele-specific epigenetic modifications such as CpG dinucleotide methylation. These modifications are referred to as epigenetic modifications (also referred to as epigenetic "marks").

Question 6

You are studying the changes that have occurred in the genomes of members of a family susceptible to an inherited form of liver cancer. You find that afflicted family members harbor a mutation in the zinc-finger motif of a cell-cycle regulatory gene. Which of the following is the most likely result of this mutation?

Accepted Answer

The zinc-finger motif is a structural motif that interacts with DNA. A mutation in this motif would likely affect the binding of a transcription factor to a DNA sequence, leading to decreased binding. The zinc finger domain is a DNAbinding motif consisting of specific spacings of cysteine and histidine residues that allow the protein to bind zinc atoms. The metal atom coordinates the sequences around the cysteine and histidine residues into a fingerlike domain. The finger domains can interdigitate into the major groove of the DNA helix. The spacing of the zinc finger domain in this class of transcription factor coincides with a half turn of the double helix.

Question 7

Homeobox (HOX) genes play a role in controlling events of embryogenesis. These genes exert their functions through which of the following processes?

Accepted Answer

Homeobox (HOX) genes are transcription factors that regulate the expression of other genes, thereby controlling the transcription process during embryogenesis. HOX genes are a group of related genes that control the body plan of the embryo. All of the proteins encoded by the HOX genes are transcription factors that contain a DNA-binding domain and function by binding to specific target genes and regulating their rate of transcription.

Question 8

Classically it was considered that each gene encoded one protein, the so-called one gene-one enzyme hypothesis. However, this model was modified as a result of the discovery of which of the following?

Accepted Answer

The discovery of alternative splicing showed that a single gene could produce multiple protein isoforms, modifying the one gene-one enzyme hypothesis.  The precise splicing outcome of a transcribed gene is controlled by complex interactions between cis-regulatory splicing signals and trans-acting regulators. Alternative splicing is a prevalent mechanism for generating transcriptome and proteome diversity. Alternative splicing can modulate gene function, affect organismal phenotype, and cause disease.

Question 9

All cells contain the same compliment of DNA. However, adipose tissue cells and gastrointestinal epithelial cells are not composed of the same proteins. The differences in these cells, as well as all other cells, is most likely a result of differences in which of the following?

Accepted Answer

The differences in proteins between adipose tissue cells and gastrointestinal epithelial cells are due to differences in mRNA expression, which determines which proteins are synthesized.  The differentiation of cells into specific types, such as adipocytes and intestinal enterocytes, is the result of the pattern of genes that are allowed to be expressed in each cell type. This means that each distinct type of cell contains a unique and distinct set of mRNAs, directing the synthesis of cell-type specific proteins.

Question 10

You are studying the effects of exposure of mouse embryos to various concentration of retinoic acid. Your studies show that the developmental malformations you observe are due to retinoic acid-induced changes in the expression of several homeobox (HOX) genes. Both retinoic acid receptors and HOX gene products recognize and bind to specific DNA sequences at numerous sites on multiple chromosomes. Which of the following best describes the function of these molecules?

Accepted Answer

Retinoic acid receptors and HOX gene products function as transcription factors, which bind to specific DNA sequences to regulate gene expression.  Retinoic acid binds to a family of nuclear receptors called the retinoic acid receptors (RARs). Like all nuclear receptors, the RARs are ligandand DNA-binding transcription factors. All of the proteins encoded by the HOX genes are also transcription factors that contain a DNA-binding domain and function by binding to specific target genes and regulating their rate of transcription.

Quiz 36: Transcription: RNA Synthesis, Processing, and Regulation