Gene Expression Bio Questions

In the diagrams below, the horizontal line represents the lac operon and the bent arrow represents the transcription start site of the lac operon. Which of the following diagrams best represents the scenario in which lactose is available to the cell and glucose is absent?

Lactose binded to repressor protein; repressor protein is not bound to the operon; RNA polymerase is synthesizing mRNA

The following the DNA sequence is a small part of the coding (nontemplate) strand from the open reading frame of β-hemoglobin gene. Given the codon chart listed below, what would be the effect of a mutation that deletes the G at the beginning of the DNA sequence?

The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point.

Which of the following messenger RNA sequences could code for both of the two amino acid sequences above, simply by a shift in the reading frame?

. . . AGCAGCAGCAGC . . .

Cells that contain only circular chromosomes are most probably which of the following?

Bacterial cells

Enzyme used during replication to attach Okazaki fragments to each other

DNA ligase.

Which of the following is most likely to create genetic variation in a population?

DNA polymerase errors during replication

Which of the following modifications of the DNA would produce the greatest change in the primary structure of the polypeptide chain?

Deleting the first T in the second triplet

Enzyme used in the synthesis of mRNA

RNA polymerase

Process in which a protein is assembled at a ribosome

Translation

The mRNA transcribed from the DNA would read

5' AUC AAG UUU GGC GCA UUG UAA 3'

The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following is the most likely consequence of a mutation at the operator locus that prevents binding of the repressor protein?

Beta-galactosidase will be produced, even in the absence of lactose.

Which of the following correctly explains where DNA replication will begin on the strand oriented 5'→3', reading from left to right?

DNA replication will be initiated immediately to the left of the RNA, since DNA polymerase requires an RNA primer. Correct. The RNA primer marks the beginning of DNA synthesis in the 5'5′ to 3'3′ direction. There is only one RNA primer present on the top strand in the diagram so DNA replication will begin there.

When DNA replicates, each strand of the original DNA molecule is used as a template for the synthesis of a second, complementary strand. Which of the following figures most accurately illustrates enzyme-mediated synthesis of new DNA at a replication fork?

Discontinuous replication on top strand (moving away from the fork) and continuous replication on bottom strand (moving towards the fork). This option is correct. It demonstrates an understanding of the structure of DNA and the process of replication. The two strands of the DNA molecule run antiparallel to each other; the 5' end of one strand pairs with the 3' end of the other strand. Replication is semi-conservative, with each strand serving as the template for the creation of new complementary strands. Helicase unzips the DNA molecules between the hydrogen bonds connecting the two strands. DNA polymerase "reads" each template strand in the 3'-to-5' direction and assembles the growing DNA chain in a 5'-to-3' direction. The "leading" strand is produced continuously, but on the "lagging" strand, Okazaki fragments are produced and are connected by ligase to produce the daughter molecule.

Based on the universal genetic code, which of the following represents the correct polypeptide that will result from translation of the mRNA molecule shown, beginning with the first available start codon?

Met−Val−Thr−Lys−Phe−Gly−His

Mutations in DNA are usually caused by chemical or radiation damage to DNA molecules, followed by imperfect repair of the damage. Immediately after this kind of imperfect repair, there may be a mismatched base pair in the DNA. The illustration below shows an example of a mismatch, with the relevant pair bases in bold. Which of the following best represents the DNA of the two daughter cells produced when a bacterial cell with this particular mismatch replicates its DNA and divides?

Mutant- A and T; Normal- G and C

A model of a process involving nucleic acids is shown in Figure 1. Which of the following best explains what process is represented in Figure 1 ?

New DNA strands are being synthesized in the 5' to 3' direction from their DNA templates. Correct. New DNA strands are synthesized in the 5' to 3' direction from the DNA template, and this is depicted in the diagram. The leading strand is being synthesized on the bottom, while the lagging strand is being synthesized in fragments on top.

Which of the following best describes an event during step 2 in the simplified model above?

Noncoding sequences are removed from a newly synthesized RNA molecule.

The p53 protein regulates a cellular response to DNA damage. Based on the diagram above, which of the following best describes the role of p53 in the response to DNA damage?

Phosphorylated p53 stimulates transcription of p21, and the the resulting p21 protein suppressed cell division until DNA damage is repaired.

Genetic engineering techniques can be used when analyzing and manipulating DNA and RNA. Scientists used gel electrophoresis to study transcription of gene L and discovered that mRNA strands of three different lengths are consistently produced.

Pre-mRNA of gene L is subject to alternative splicing, so three mRNA sequences are possible. Correct. Excision of different introns and splicing and retention of different exons can generate different versions of the resulting mRNA, which may have different lengths.

The figure above depicts the DNA-protein complex that is assembled at the transcriptional start site of gene X when the expression of gene X is activated in liver cells. Previous studies have shown that gene X is never expressed in nerve cells. Based on the diagram, which of the following most likely contributes to the specific expression pattern of gene X ?

The activator is a sequence-specific DNA-binding protein that is present in some tissues but not in other tissues.

Figure 1 represents part of a process essential to gene expression. Which of the following best explains what strand X represents?

The antisense strand, because it is serving as a template. Correct. Strand X is serving as the template strand for the synthesis of a complementary strand of RNA. The template strand is also called the antisense strand.

Figure 1 represents part of a process that occurs in eukaryotic cells. There are untranslated regions (UTR) in this sequence. Which of the following best explains the process represented by Figure 1 ?

The enzyme-regulated processing of pre‑mRNA into mature mRNA. Correct. The removal of introns and the addition of a 3′ poly‑AA tail and a 5′GTP cap are associated with mRNA processing in eukaryotic cells, and the diagram reflects these changes.

Figure 1 shows some relevant details of a model of how a deoxynucleotide, in this case dTMP, is added to a growing strand of DNA. The features of this model provide evidence for which explanation of why all growing strands are synthesized in a 5′ to 3′ direction?

The phosphate group, attached to the 5′ carbon of the dTMP, forms a covalent bond with the oxygen atom attached to the 3′ carbon of the growing strand. Correct. Synthesizing a growing strand requires the interaction of the phosphate groups found at the 5′5′ location on the new deoxynucleotide with the OH group attached to the 3′3′ carbon of the existing end of the growing strand. These specific interactions and the release of diphosphate explain the directionality requirement for a growing strand of DNA.

Process in which RNA is produced by using a DNA template

Transcription

Analysis of DNA sequences from two individuals of the same species results in a greater estimate of genetic variability than does analysis of amino acid sequences from the same individuals because

different DNA sequences can code for the same amino acid

tRNA molecules deliver amino acids to ribosomes where the amino acid next

is covalently bonded to a growing polypeptide

Maximal transcription of the lac operon requires

the presence of cyclic AMP and lactose

A scientist is using an ampicillin-sensitive strain of bacteria that cannot use lactose because it has a nonfunctional gene in the lac operon. She has two plasmids. One contains a functional copy of the affected gene of the lac operon, and the other contains the gene for ampicillin resistance. Using restrictions enzymes and DNA ligase, she forms a recombinant plasmid containing both genes. She then adds a high concentration of the plasmid to a tube of the bacteria in a medium for bacterial growth that contains glucose as the only energy source. This tube (+) and a control tube (-) with similar bacteria but no plasmid are both incubated under the appropriate conditions for growth and plasmid uptake. The scientist then spreads a sample of each bacterial culture (+ and -) on each of the three types of plates indicated below. If the scientist had forgotten to use DNA ligase during the preparation of the recombinant plasmid, bacterial growth would most likely have occurred on which of the following?

1 and 4 only

Erwin Chargaff investigated the nucleotide composition of DNA. He analyzed DNA from various organisms and measured the relative amounts of adenine (A), guanine (G), cytosine (C), and thymine (T) present in the DNA of each organism. Table 1 contains a selected data set of his results. Which of the following statements best explains the data set?

Since the %A and the %T are approximately the same in each sample, adenine and thymine molecules must pair up in a double-stranded. DNA molecule. Correct. The percentages of adenine and thymine are approximately the same because adenine aligns with thymine in double-stranded DNA and they are therefore present in each organism in the same amounts.

Nuclear pores regulate the passage of substances into and out of the nucleus. Antibodies such as mAb414 have been used to inhibit the movement of substances through the nuclear pores of rat liver cells. Scientists cultured rat liver cells (eukaryotic) and bacteria cells (prokaryotic) in separate dishes with radioactively labeled amino acids. A specific gene in both cell types was engineered to synthesize identical polypeptide chains, and translation of this gene was measured. The procedure was repeated with mAb414 (the inhibitor) added to each of the two cell cultures, and translation was monitored again. Which of the following sets of graphs best summarizes the results of the experiments?

Prokaryotic- goes up and constant; eukaryotic- stay the same/ flat (horizontal line). Correct. In eukaryotes, transcription and translation occur at different areas in the cell, whereas in prokaryotes, they occur simultaneously. In the experimental dish with the eukaryotes, the drug inhibited the translocation of mRNA to the cytoplasm, thereby preventing the translation, so no polypeptide chain was formed. However, in the prokaryotes, with no nucleus and both processes occurring simultaneously, translation occurred and the polypeptide chain was formed.

Which of the following DNA strands will code for the amino acid sequence shown above?

. . . CCTTCGCCT . . .

Enzyme used to position nucleotides during DNA replication

DNA polymerase

A model that represents a process occurring in a cell of a particular organism is shown in Figure 1. Which of the following correctly explains the process shown in Figure 1 ?

Initiation of transcription is occurring because a strand of RNA is being produced from a DNA template strand. Correct. Transcription is occurring. Since uracil (U) is present in the new strand being formed, RNA is being formed from a DNA template.

Lactose digestion in E. coli begins with its hydrolysis by the enzyme β-galactosidase. The gene encoding β-galactosidase, lacZ, is part of a coordinately regulated operon containing other genes required for lactose utilization. Which of the following figures correctly depicts the interactions at the lac operon when lactose is NOT being utilized? (The legend below defines the shapes of the molecules illustrated in the options.)

No RNA polymerase or lactose present. The repressor protein is bound to the operator portion of the operon. This option is correct because the lac operon is an inducible operon, which means that the regulatory system is turned off until lactose or its analog turns it on. The mechanism for preventing its transcription is the binding of a repressor protein to the operator region.

Which of the following normally leads to the production of functional messenger RNA in eukaryotic cells?

The removal of portions of RNA known as intervening sequences (introns)

Figure 1 represents a metabolic process involving the regulation of lactose metabolism by E. coli bacteria. Lactose is utilized for energy by E. coli when glucose is not present. Allolactose is an isomer of lactose that is in the environment of these bacteria when lactose is present. The CAP site prevents the binding of RNA polymerase when glucose is present in the environment. The lacZ, lacY, and lacA genes code for proteins needed for lactose metabolism. Which is a scientific claim that is consistent with the information provided and Figure 1 ?

When bound to the operator, the repressor protein prevents lactose metabolism in E. coli. Correct. When the repressor protein is bound to the operator, the lac operon is turned off and the genes for lactose metabolism cannot be transcribed.