AP Practice #1 2023

Oncogenes are genes that can cause tumor formation as a result of a particular mutation. Which of the following potential therapies would be most effective at preventing the expression of an oncogene?

• Reducing the number of ribosomes in the cell to prevent the creation of the oncogene’s proteins

• Blocking membrane-bound receptors of transcription factors

• Introducing a chemical that binds to transcription factors associated with the oncogene’s promoter

• Producing additional transcription factors for tumor suppressor genes in the cell

Answer explanation

If a transcription factor is bound to a chemical, it cannot bind to the oncogene promoter, thus preventing gene expression that would result in tumor formation.

Ultraviolet (UV) radiation can damage DNA by breaking weak bonds. Which of the following best explains how this occurs?

• UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs.

• UV radiation disrupts the double helix structure by breaking the covalent bonds between the nitrogenous base pairs.

• UV radiation is able to break DNA strands in two by breaking covalent bonds between the sugar-phosphate backbone molecules.

• UV radiation is able to break DNA strands in two by breaking hydrogen bonds between the sugar-phosphate backbone molecules.

Answer explanation

Hydrogen bonds, like those found between nitrogenous base pairs, are weaker than covalent bonds and are easily broken by UV radiation.

Scientists are interested in determining the evolution of seven lizard species found on different islands of the Canary Island group. They isolated DNA from individuals of each species and sequenced the mitochondrial gene that encodes cytochrome b. The numbers of genetic differences between species are shown in the table.

Based on the table which two lizard species are most closely related?

• C and B

• E and D

• F and B

• G and A

Answer explanation

Which species have the fewest mitochondrial genetic differences?

Figure 1 shows a model of the endocrine signaling pathway that regulates ovulation. Which of the following observations would provide evidence of a positive feedback mechanism in this system?

• Estrogen from the ovaries inhibits the release of GnRH from the hypothalamus.

• Progesterone from the ovaries stimulates the thickening of the uterine lining.

• Progesterone from the ovaries inhibits the release of LH and FSH from the anterior pituitary.

• Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.

Answer explanation

Which choice describes an observation in which the production of estrogen stimulates systems at earlier stages in the signaling pathway to produce hormones that further stimulate the ovaries?

A scientist designed an experiment to test an artificial membrane that mimics the phospholipid bilayer of a cell.

The scientist built a tube that was divided by an artificial membrane and filled with distilled water. The scientist put a known amount of a protein into the water on one side of the membrane. After some time, the scientist measured the concentration of the protein on either side of the membrane but found that there had been no change.

Which of the following experimental changes would allow the scientist to observe transport of a solute across the artificial membrane?

• Increase the solute concentration in the solution

• Use a small, nonpolar solute instead of a protein

• Increase the temperature of the solution

• Add artificial aquaporins to the membrane

Answer explanation

Small, nonpolar molecules are able to diffuse through cell membranes, while large proteins are not.

Which of the following best illustrates the flow of information required for the synthesis of proteins encoded in the genome of a retrovirus?

• DNA --> RNA --> protein

• RNA --> DNA --> protein

• RNA --> DNA --> RNA --> protein

• DNA --> RNA --> DNA --> protein

Answer explanation

The genome of a retrovirus is composed of RNA. It must first be reverse-transcribed into DNA and integrated into a host cell’s DNA before it is transcribed and the RNA is translated.

Which of the following best describes the process by which gas from the atmosphere is obtained by plants and used to build lipids?

• Gas is fixed by plants as part of the sulfur cycle.

• Gas is fixed by plants as part of the nitrogen cycle.

• Gas is directly obtained by plants as part of the carbon cycle.

• Gas is directly obtained by plants as part of the magnesium cycle.

Answer explanation

Lipids are made of hydrocarbon chains whose main component is carbon. Plants obtain this carbon directly from the atmosphere in the form of carbon dioxide.

Which of the following best explains how the phospholipid bilayer of a transport vesicle contributes to cellular functions?

• The phospholipid bilayer allows the vesicle to fuse with the Golgi apparatus and the plasma membrane, allowing the exocytosis of proteins.

• The phospholipid bilayer physically connects the nuclear envelope to the rough endoplasmic reticulum, thus increasing the rate of transcription and translation.

• The phospholipid bilayer of a transport vesicle contains chemicals that digest the proteins made in the rough endoplasmic reticulum.

• The phospholipid bilayer contains enzymes that catalyze the conversion of hydrogen peroxide to water and oxygen.

Answer explanation

The phospholipid bilayer allows for the transport of proteins from inside the cell to outside through the use of vesicles.

The diploid number of chromosomes in the cell of a domesticated dog is 78. Which of the following options includes the correct number of chromosomes in a cell after each cellular process (G2 checkpoint, meiosis, and fertilization, respectively)?

• 
• 
• 
• 

Answer explanation

Which choice correctly identifies: although chromatids are duplicated after the G2 checkpoint, they still form 78 chromosome pairs. After meiosis, the chromosome number is divided in half. After fertilization, the chromosomes from two gametes are combined to form 78 chromosomes.

Scientists were interested in testing the effects of rotenone, a broad-spectrum pesticide, on a cell culture. Cell culture A was used as a control, while culture B was treated with rotenone. After a period of time, the scientists measured the concentration of several metabolites in the mitochondria of cells in both cultures. Their results are shown in the table below.

Based on the data in the table, which of the following best explains the effects of rotenone on cellular respiration?

• Rotenone acts as an inhibitor of the enzymes in the Krebs cycle.

• NADH, produced during glycolysis, is not able to enter the mitochondria because transport proteins are blocked from entering.

• Treated cells are not able to break down NADH because certain enzymes of the electron transport chain are inhibited.

• Rotenone acts as an allosteric inhibitor of glycolytic enzymes, thus inhibiting cellular respiration.

Answer explanation

The data indicate that NADH concentrations are significantly increased in cell culture B.