BIG QUIZ-AP clsrm (unit 5/6)

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. 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.

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. 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?

(Answer is attached image) 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.

Figure 1 illustrates a model of the molecules involved in DNA replication and their placement relative to each other. 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. The RNA primer marks the beginning of DNA synthesis in the 5' to 3′ direction. There is only one RNA primer present on the top strand in the diagram so DNA replication will begin there.

Which of the following statements best explains the structure and importance of plasmids to prokaryotes?

Plasmids are circular, double-stranded DNA molecules that provide genes that may aid in survival of the prokaryotic cell. Plasmids are small, circular, double-stranded DNA molecules. Plasmids can be acquired and can be replicated by prokaryotes. Plasmids may carry genes, such as antibiotic resistance genes, that may help the prokaryote survive.

Antibiotics interfere with prokaryotic cell functions. Streptomycin is an antibiotic that affects the small ribosomal subunit in prokaryotes. Specifically, streptomycin interferes with the proper binding of tRNA to mRNA in prokaryotic ribosomes. Which of the following best predicts the most direct effect of exposing prokaryotic cells to streptomycin?

Synthesis of polypeptides will be inhibited. Translation of mRNA involves assembling polypeptides from amino acids attached to tRNA specific for each amino acid. Streptomycin prevents the ribosome from interacting properly with tRNA, preventing the synthesis of needed proteins and leading to the death of the prokaryote.

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 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 The removal of introns and the addition of a 3′ poly‑A tail and a 5′ GTP cap are associated with mRNA processing in eukaryotic cells, and the diagram reflects these changes.

Antibiotics can be used to kill the specific pathogenic bacterium, Mycobacterium tuberculosis, that causes tuberculosis. The appearance of antibiotic-resistant strains has made it more difficult to cure M. tuberculosis infections. These antibiotic-resistant bacteria survive and pass on the genes to their offspring, making the resistant phenotype more common in the population. DNA analysis indicates that the genes for antibiotic resistance are not normally present in bacterial chromosomal DNA. Which of the following statements best explains how the genes for antibiotic resistance can be transmitted between bacteria without the exchange of bacterial chromosomal DNA?

The genes for antibiotic resistance are located on a plasmid that can be passed to neighboring bacteria. Bacteria can exchange and express the genes found on plasmids, which are foreign, extrachromosomal loops of DNA that they pick up. Genes for antibiotic resistance are located on these plasmids.

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. Figure 1. Model showing details of adding a deoxythymidine monophosphate (dTMP) nucleotide 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. Synthesizing a growing strand requires the interaction of the phosphate groups found at the 5′ location on the new deoxynucleotide with the OHOH group attached to the 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.

Molecular biologists are studying the processes of transcription and translation and have found that they are very similar in prokaryotes and eukaryotes, as summarized in Table 1. Based on the information in Table 1, which of the following best predicts a key difference in prokaryotes and eukaryotes with regard to transcription and translation?

The two processes will occur simultaneously in prokaryotes but not eukaryotes. Since transcription and translation both occur in the cytoplasm, they can occur simultaneously in prokaryotes. Note that the spatial separation of these two processes in eukaryotes increases the capacity for gene regulation.