Biology Review

Which of the following best explains how the pattern of DNA arrangement in chromosomes could he used in most cases, to determine if an organism was a prokarvote or a eukarvote?

(D) Prokarvotic DNA: singular circular chromosome Eukarvotic DNA: multiple linear chromosomes

Labeled nucleotides were supplied to a cell culture before the cells began DNA replication. A simplified representation of the process for a short segment of DNA is shown in Figure 1. Labeled DNA bases are indicated with an asterisk (*). Figure 1. A simplified representation of the DNA replication process Which of the following best helos explain how the process represented in Figure 1 produces DNA molecules that are hvbrids of the original and the newlv sunthesized strands?

(D) Each newlv synthesized strand remains associated with its template strand to form two copies of the original DNA molecule.

Lynch syndrome is an inherited condition associated with an increased risk for colon cancer, as well as certain other cancers. Mutations in one of several genes involved in DNA repair during DNA replication have been associated with Lunch syndrome. DNA sequencing was performed for an individual. The results indicated that the individual carries one of the dominant alleles that has been associated with Lunch syndrome. Which of the following best explains how the results should be interpreted?

(B) the individual has an increased risk of developing colon cancer. Which of the following best explains how the results should be interpreted?

Scientists conducted a transformation experiment using E. coli bacteria and the pTru plasmid. Samples of the Tru plasmid (lane A) and the chromosomal DNA from two different E. coli strains that the scientists attempted to transform (lane B and lane C) were compared usina gel electrophoresis. The results are shown in Figure 1. Figure 1. Results of E. coli transformation with pTru plasmid Which of the following statements best explains the experimental results observed in Figure 1?

(C) E. coli in lane C have been successfully transformed and contain additional genetic information.

An evolutionary biologist hypothesizes that two morphologicallv similar plant species are not closelv related To test the hypothesis, the biologist collects DNA samples from each of the two plant species and then uses restriction enzymes to cut the DNA samples into fragments which are then subiected to gel electrophoresis. The results are shown in Fiqure 1. Figure 1. DNA analvsis of two species Given the results shown in Figure 1, which of the following correctlv describes a relationship between the two species?

(C) Species B has more short fragments of DNA than species A does.

Retroviruses such as HIV and hepatitis B virus Use RNA as their genetic material rather than DNA. In addition, they contain molecules of reverse transcriptase, an enzyme that uses an RNA template to synthesize complementarv DNA Which of the following best predicts what will happen when a normal cell is exposed to a retrovirus?

(C) The reverse transcriptase will produce DNA from the viral RNA, which can be incorporated into the host's genome and then transcribed and translated.

Cycloheximide (CHX) is a eukaryote protein synthesis inhibitor. It is used in biomedical research to inhibit protein synthesis in eukaryotic cells studied in vitro. Its effects are rapidly reversed by simply removing it from the culture medium. In a translation experiment using a fungus culture, radiolabeled amino acids were added to the culture, allowing the researchers to measure the growth of a single polvpeptide chain by measuring counts per minute (CPM). As the chain arew, the CPM increased. After a certain amount of time CHY was added to the mixture, and the experiment continued. After an additional amount of time, the CHX was removed from the culture medium. Which of the following graphs best predicts the data collected during the experiment?

(D) (graph CPM x Time) increase=> Inhibitor added=> constant=> inhibitor removed=> decrease

Exposure to ultraviolet (UV) radiation is the leading cause of skin cancer in humans. Figure I shows a model of how UV exposure damages DNA Figure 1. Model of damage to DNA caused by UV exposure Which of the following statements best exolains what is shown in Figure 1?

(D) UV photons cause dimers to form, leading to misshapen DNA, which results in replication and transcription errors

The tro operon in E. coli is an example of a repressible operon that consists of genes coding for enzymes used to synthesize tryptophan. When tryptophan levels are high, the operon is turned off and these genes are not transcribed. However, it is also known that tryptophan does not bind directly to the operator DNA sequence. A regulatory gene called troR has also been discovered although it is not part of the tro operon. The proposed model of how tryptophan acts as a corepressor is shown in Figure 1. Figure 1. Model of proposed requlation of the tro operon bu corepressors tro repressor and tryptophan boitalbits Which of the following evidence best supports a claim that tryptophan functions as a corepressor?

(D) When troR is mutated, the trp operon is transcribed regardless of tryptophan levels.

Both liver cells and lens cells have the gene for making the proteins 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? A.) Liver cells possess transcriptional activators that are different from those of lens cells B.) Liver cells and lens use different RNA polymerase enzymes to transcribe DNA C.) Liver cells possess the same transcriptional activators D.) Liver cells and lens cells possess different general transcription factors.

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

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 operon of three different bacteria. E.coli R773 is found in environment with low arsenic levels. Herminiimonas arsenicoxydans and Ochrobacteruim tritici are both found in arsenic-rich environments. Researchers claim that bacteria that live in environments heavily contaminated with arsenic into arsenic into arsenite and removing this toxin from their cells. Justify this claim based on the evidence shown in Figure 1. A.)There are multiple operons controlling the production of proteins that process and remove arsenite from cells in both H.arsenicoxydarus and O. tritici. In contrast E.coli has only operon devoted to arsenic removal. B.)Both H.aresenicoxydarus and O. triciti contain the ar s R gene codes for a repressor that turns on the operon to eliminate arsenite from the cell. C.) Both O. tritici and E.coli contain the ar s D gene, which codes for a protein that helps remove arsenite from the cell. D.)Both H.aresenicoxydarus and O. tritici have more arsenic resistance genes than has E.coli

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

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 ell using a phytochrome. Figures 1 and 2 represent findings from the study. Using the response 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. A.)When inactive phytochromes Pr is activated by red light to become phytochrome Per, it is transported into the nucleus where it binds to the transcription factor PIF3 at the promoter. This stimulates transcription, ultimately leading to the 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 activates the transcription, ultimately leading to protein production. Red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3. C.) MYB, and not Per, is activated by red light, causing it to bind to the promoter and stimulates 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.

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

The enzyme lactase aids in the digestion of lactose, a sugar found in the milk of most mammals. In most mammal species, adults do not produce lactase. Continuing to produce lactase into adulthood in people is called lactase persistence. A number of different alleles have been identified that results in lactase persistence. Figure 1 shows the percentage of people in different geographic areas parts of the Old World that exhibits lactase persistence. Which of the following best explains the distribution of lacatase persistence in the areas shown in Figure 1? A.) Lactase persistence developed because people were malnourished in Europe. B.) Lactase persistence alleles are present in all humans populations and are expressed when lactose is consumed. C.) Mutations conferring lactase persistence likely arose independently in different geographic areas and offered a selective advantage D.) The mutations are detrimental to humans and will eventually disappear from the gene pool.

C.) Mutations conferring lactase persistence likely arose independently in different geographic areas and offered a selective advantage

Sickle-cell anemia is an inherited blood disorder in which one of the hemoglobin subunits is replaced with a different form of hemoglobin. Partial DNA sequences of the HBB gene for normal hemoglobin and for sickle-cell hemoglobin are shown in Figure 1. Which of the following best describes the type of mutation shown in Figure 1 that leads to sickle-cell anemia? A.) Insertion B.)Deletion C.)Substitution D.)Frameshift

C.)Substitution

Nondisjunction during meiosis can negatively affect gamete information. A model showing a possible nondisjunction event and its impact on gamete formation is shown in Figure 1. Which of the following best describes the most likely impact on an individual produced from fertilization between one of the daughter cells shown and a normal gamete? A.) Because nondisjunction occurred in anaphase 1, all gametes will be normal and the resulting individual will be phenotypically normal. B.)Because nondisjunction occurred in anaphase 1, all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event. C.) Because nondisjunction occurred in anaphase 2, all gametes will be normal and the resulting individual will be phenotypically normal. D.)Because nondisjunction occurred in anaphase 2, all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event.

D.)Because nondisjunction occurred in anaphase 2, all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event.