Unit 6 Review 𖦹⋆｡°✩

Question 1

Erwin Chargaff investigated the nucleotide composition of DNA. He analyzed DNA from various organisms and measured the relative amounts of adenine, guanine, cytosine, and thymine 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?

Answer 1

A. Since the %A and the %G add up to approximately 50 percent in each sample, adenine and guanine molecules must pair up in a double-stranded DNA molecule.

B. 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.

C. Since the %(A+T) is greater than the %(G+C) in each sample, molecules must have a poly-A tail at one end.

D. Since the %C and the %T add up to approximately 50 percent in each sample, cytosine and thymine molecules must both contain a single ring.

Question 2

✩CORRECT ANSWER FOR 6.1, 1✩

Answer 2

B

Question 3

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?

Answer 3

A. The antibiotic-resistant bacteria release a hormone that signals neighboring bacteria to become resistant.

B. The genes for antibiotic resistance are located on a plasmid that can be passed to neighboring bacteria.

C. The antibiotic-resistant bacteria are the result of bacteria that specifically modify their own chromosomal DNA to neutralize the antibiotics.

D. The antibiotic alters the bacterial genome of each bacterium, which results in an antibiotic-resistant population.

Question 4

✩CORRECT ANSWER FOR 6.1, 2✩

Answer 4

B

Question 5

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

Answer 5

A. Plasmids are circular, single-stranded RNA
molecules that transfer information from the prokaryotic chromosome to the ribosomes during protein synthesis.

B. Plasmids are circular, double-stranded DNA molecules that provide genes that may aid in survival of the prokaryotic cell.

C. Plasmids are single-stranded DNA molecules, which are replicated from the prokaryotic chromosome, that prevent viral reproduction within the prokaryotic cell.

D. Plasmids are double-stranded RNA
molecules that are transmitted by conjugation that enable other prokaryotic cells to acquire useful genes.

Question 6

✩CORRECT ANSWER FOR 6.1, 3✩

Answer 6

B

Question 7

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 ?

Answer 7

A. New DNA strands are being synthesized in the 3’ to 5’ direction from their
templates.

B. New DNA strands are being synthesized in the 5’ to 3’ direction from their
templates.

C. A new RNA strand is being synthesized in the 3’ to 5’ end from its
template.

D. Two new RNA strands are being synthesized in both directions from their DNA templates.

Question 8

✩CORRECT ANSWER FOR 6.2, 1✩

Answer 8

B

Question 9

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 the 5’ to 3’ direction?

Answer 9

A. The two strands need to be antiparallel to bond properly.

B. Thymine and adenine would not bond properly if the strand grew from 3’ to 5’.

C. The translation of mRNA occurs in the 5’ to 3’ direction; therefore, the growing
strand must also grow in the 5’ to 3’ direction.

D. 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.

Question 10

✩CORRECT ANSWER FOR 6.2, 2✩

Answer 10

D

Question 11

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?

Answer 11

A. DNA replication will be randomly initiated along the unwound portion of the DNA strand since base pairing will occur.

B. DNA replication cannot occur since there is already RNA base pairing with the template strand.

C. DNA replication will be initiated immediately to the left of the RNA, since
polymerase requires an RNA primer.

D. DNA replication will be initiated at the site of the topoisomerase since that is where DNA begins to uncoil.

Question 12

✩CORRECT ANSWER FOR 6.2, 3✩

Answer 12

C

Question 13

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?

Answer 13

A. DNA replication is occurring because replication is semi-conservative and the new strand is a copy of the template strand.

B. Initiation of transcription is occurring because a strand of RNA is being produced from a DNA template strand.

C. Translation is occurring because the two strands have separated and a new strand is being produced.

D. Alternative splicing of mRNA is occurring because the mRNA strand is being synthesized from only one strand of DNA

Question 14

✩CORRECT ANSWER FOR 6.3, 1✩

Answer 14

B

Question 15

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?

Answer 15

A. The synthesis of mRNA in the 5’ to 3’ direction from DNA

B. The modification of a protein to produce a functional form of that protein

C. The translation of an mRNA molecule into a polypeptide

D. The enzyme-regulated processing of pre‑mRNA into mature mRNA

Question 16

✩CORRECT ANSWER FOR 6.3, 2✩

Answer 16

D

Question 17

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

Answer 17

A. A complementary RNA sequence, because it contains thymine

B. The coding strand in this process, because it is being read 3’ to 5’

C. The antisense strand, because it is serving as a template

D. The pre‑mRNA, because it does not yet have a
cap

Question 18

✩CORRECT ANSWER FOR 6.3, 3✩

Answer 18

C

Question 19

✩WAITING ON TRANSLATION QUIZ RESULTS✩

Question 20

Histone methyltransferases are a class of enzymes that methylate certain amino acid sequences in histone proteins. A research team found that transcription of gene R decreases when histone methyltransferase activity is inhibited. Which scientific claim is most consistent with these findings?

Answer 20

A. DNA methylation inhibits transcription of gene R.

B. Histone modifications of genes are usually not reversible.

C. Histone methylation condenses the chromatin at gene R so transcription factors cannot bind to DNA.

D. Histone methylation opens up chromatin at gene R so transcription factors can bind to DNA more easily.

Question 21

✩CORRECT ANSWER FOR 6.5, 1✩

Answer 21

D

Question 22

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 ?

Answer 22

A. The presence of excess lactose blocks the functioning of RNA polymerase in this operon.

B. When bound to the operator, the repressor protein prevents lactose metabolism in E. coli.

C. The binding of the repressor protein to the operator enables E. coli to metabolize lactose.

D. Allolactose acts as an inducer that binds to the operator, allowing E. coli to metabolize lactose.

Question 23

✩CORRECT ANSWER FOR 6.5, 2✩

Answer 23

B

Question 24

Figure 1 illustrates processes related to control of transcription and translation in a cell. Which of the following scientific claims is most consistent with the information provided in Figure 1 ?

Answer 24

A. Gene X codes for a transcription factor required for transcription of gene D.

B. A single transcription factor regulates transcription similarly, regardless of the specific gene.

C. Transcription of genes A, B, and C is necessary to transcribe gene E.

D. Different genes may be regulated by the same transcription factor.

Question 25

✩CORRECT ANSWER FOR 6.5, 3✩

Answer 25

D

Question 26

Arsenic is a toxic element found in both aquatic and terrestrial environments. Scientists have found genes that allow bacteria to remove arsenic from their cytoplasm. Arsenic enters cells as arsenate that must be converted to arsenite to leave cells. Figure 1 provides a summary of the arsenic resistance genes found in the operons of three different bacteria. E. coli R773 is found in environments with low arsenic levels. Herminiimonas arsenicoxydans and Ochrobactrum tritici are both found in arsenic‑rich environments. Researchers claim that bacteria that live in environments heavily contaminated with arsenic are more efficient at processing arsenic into arsenite and removing this toxin from their cells. Justify this claim based on the evidence shown in Figure 1.

Answer 26

A. There are multiple operons controlling the production of proteins that process and remove arsenite from cells in both H. arsenicoxydans and O. tritici. In contrast, E. coli has only one operon devoted to arsenic removal.

B. Both H. arsenicoxydans and O. tritici contain the arsR gene that codes for a repressor that turns on the operon to eliminate arsenite from the cell.

C. Both O. tritici and E. coli contain the arsD
gene, which codes for a protein that helps remove arsenite from the cell.

D. Both H. arsenicoxydans and O. tritici. have more arsenic resistance genes than has E. coli.

Question 27

✩CORRECT ANSWER FOR 6.6, 1✩

Answer 27

A

Question 28

Both liver cells and lens cells have the genes for making the proteins albumin and crystalline. However, only liver cells express the blood protein albumin and only lens cells express crystalline, the main protein in the lens of the eye. Both of these genes have enhancer sequences associated with them. The claim that gene regulation results in differential gene expression and influences cellular products (albumin or crystalline) is best supported by evidence in which of the following statements?

Answer 28

A. Liver cells possess transcriptional activators that are different from those of lens cells.

B. Liver cells and lens cells use different RNA polymerase enzymes to transcribe DNA.

C. Liver cells and lens cells possess the same transcriptional activators.

D. Liver cells and lens cells possess different general transcription factors.

Question 29

✩CORRECT ANSWER FOR 6.6, 2✩

Answer 29

A

Question 30

Phytochromes are molecules that change light stimuli into chemical signals, and they are thought to target light-activated genes in plants. A study was conducted to determine how certain cell proteins were made in a plant cell using a phytochrome. Figures 1 and 2 represent findings from the study. Use the response models shown in Figures 1 and 2 to justify the claim that phytochromes regulate the transcription of genes leading to the production of certain cellular proteins.

Answer 30

A. When inactive phytochrome Pr is activated by red light to become phytochrome Pfr, it is transported into the nucleus where it binds to the transcription factor PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Far-red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3.

B. Far-red light activates phytochrome Pr, causing it to travel to the nucleus where it binds to PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3.

C. MYP, and not Pfr, is activated by red light, causing it to bind to the promoter and stimulate transcription and translation of cellular proteins.

D. PIF3 binds to the promoter only in the presence of red light and Pfr. Any time PIF3
is bound to the promoter, MYB is transcribed, initiating transcription of various other proteins in the cell.

Question 31

✩CORRECT ANSWER FOR 6.6, 3✩

Answer 31

A

Question 32

✩WAITING ON MUTATION QUIZ RESULTS✩

Question 33

Antigens are foreign proteins that invade the systems of organisms. Vaccines function by stimulating an organism’s immune system to develop antibodies against a particular antigen. Developing a vaccine involves producing an antigen that can be introduced into the organism being vaccinated and which will trigger an immune response without causing the disease associated with the antigen. Certain strains of bacteria can be used to produce antigens used in vaccines. Which of the following best explains how bacteria can be genetically engineered to produce a desired antigen?

Answer 33

A. The gene coding for the antigen can be inserted into plasmids that can be used to transform the bacteria.

B. The bacteria need to be exposed to the antigen so they can produce the antibodies.

C. The DNA of the antigen has to be transcribed in order for the mRNA produced to be inserted into the bacteria.

D. The mRNA of the antigen has to be translated in order for the protein to be inserted into the bacteria.

Question 34

✩CORRECT ANSWER FOR 6.8, 1✩

Answer 34

A

Question 35

Students subjected three samples of five different molecules to gel electrophoresis as shown in Figure 1. Which of the following statements best explains the pattern seen on the gel with regard to the size and charge of molecules A and B?

Answer 35

A. Molecules A and B are positively charged, and molecule A is smaller than molecule B.

B. Molecules A and B are positively charged, and molecule A is larger than molecule B.

C. Molecules A and B are negatively charged, and molecule A is smaller than molecule B.

D. Molecules A and B are negatively charged, and molecule A is larger than molecule B.

Question 36

✩CORRECT ANSWER FOR 6.8, 2✩

Answer 36

C

Question 37

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. Which of the following explanations best accounts for this experimental result?

Answer 37

A. Gel electrophoresis can only be used with DNA (not mRNA), so experimental results are not interpretable.

B. RNA polymerase consistently makes the same errors during transcription of gene L.

C. Gene L is mutated, so RNA polymerase does not always transcribe the correct sequence.

D. Pre-mRNA of gene L is subject to alternative splicing, so three mRNA sequences are possible.

Question 38

✩CORRECT ANSWER FOR 6.8, 3✩

Answer 38

D