Unit 4 AP Biology

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1.

Figure 1. Amount of DNA per cell during different stages of the cell cycle, relative to the beginning of the G1 stage

Which of the following best describes how the cell's DNA changes during the M phase?

• The amount of DNA doubles as the DNA is replicated.

• The amount of DNA slightly increases as a result of new organelle synthesis.

• The amount of DNA does not change while the cell grows.

• The amount of DNA is halved as the cell divides into two daughter cells.

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What is the expected percent change in the DNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1 phase to the end of the G2 phase?

• −100%

• −50%

• +50%

• +100%

Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. 

Figure 1. Number of chromosomes in a human cell at different stages of cell division

Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?

• DNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes.

• New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis.

• Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells.

• At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.

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The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells

Question

A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher’s claim?

• Epinephrine is a signaling molecule that binds to a transmembrane protein.

• The G protein in the epinephrine signaling pathway consists of three different subunits.

• Phosphorylase kinase catalyzes the hydrolysis of ATP.

• Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

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Cancer cells behave differently than normal body cells. For example, they ignore signals that tell them to stop dividing.

Which of the following conditions will most likely cause a normal body cell to become a cancer cell?

• The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.

• The environment lacks signals that would otherwise tell the cell to stop dividing.

• The environment has an abundance of nutrients.

• The environment already contains cancer cells.

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Researchers determined the average amount of time that a particular type of eukaryotic cell spends in each phase of the cell cycle. The data collected by the researchers are represented in Figure 1.

Figure 1. The average amount of time spent by a particular type of eukaryotic cell in each phase of the cell cycle

Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase?

• 5%

• 95%

• 50%

• 35%

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Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?

• The yeast cells will initiate mitosis but will fail to complete the G2G2 phase.

• The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.

• The yeast cells will transition out of G0G0 but will fail to complete the G1G1 phase.

• The yeast cells will replicate their organelles but will fail to complete the S phase.

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Scientists have hypothesized that rinsing fruit in a salicylic acid solution may damage ethylene receptors in the fruit. If these plants were then exposed to ethylene gas what results would you expect to see if the researcher’s hypothesis was supported?

• The fruit would die immediately because of the damaging effects of the salicylic acid.

• The fruit would ripen quicker after exposure to the ethylene gas than in comparison to the negative control because the receptors would be more readily able to bind to the ethylene gas thereby initiating the signal transduction cascade.

• The fruit would ripen slower after exposure to the ethylene gas than in comparison to the negative control because the receptors would be made non-functional and therefore could not bind to ethylene gas and undergo the conformational change needed to initiate the transduction process.

• None of the above would support the hypothesis of the researcher.

Phosphodiesterase plays a vital role in maintaining cell signaling pathways. Phosphodiesterase belongs to a family of enzymes that help to hydrolyze cAMP in order to regenerate other important second messenger molecules. Interestingly, caffeine is an inhibitor of phosphodiesterase. In an experiment, cells were exposed to low levels of caffeine for one hour and then analyzed. What would you predict to find in the cells after being exposed to caffeine?

• High levels of cAMP since phosphodiesterase would be unable to hydrolyze it

• High levels of protein phosphatase since the signaling pathway would shut down

• Increased levels of proteins due to increased transcription factors

• Low levels of phosphodiesterase since caffeine acts as an inhibitor to phosphodiesterase

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Which of the following is not true regarding diploid cells?

•   Diploid cells contain

  Diploid cells divide by mitosis

• Diploid cells include sex cells (egg and sperm cells)

•   Diploid cells contain two sets of chromosomes (one from mom, one from dad)

• The diploid number for humans is 2n = 46

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