Enzymes STAAR Review

Taq polymerase is an enzyme used in the polymerase chain reaction (PCR) to replicate fragments of DNA. A study published in 1976 examined the properties of Taq polymerase after the enzyme was isolated from Thermus aquaticus, a thermophilic bacterium that lives in the hot springs of Yellowstone National Park. The graph shows one of the results of the study. Which statement about enzyme activity is best supported by this graph?

• An enzyme must be composed of multiple polypeptides, or subunits, to be active.

• An enzyme’s rate of activity increases with time until it becomes inactive.

• An enzyme functions best under specific temperature conditions.

• An enzyme works equally well in bacteria that are adapted to high temperatures and in eukaryotic cells such as human cells.

Some foods that are rich in complex carbohydrates can be difficult to digest. Gas often forms as the foods are slowly digested by bacteria in the large intestine. The advertisement is for a nutritional supplement that prevents intestinal gas. Which of the following represents evidence that could be used to support the claims about this product?

• Complex carbohydrates are found in vegetables and grains, which are good sources of fiber, vitamins, antioxidants, and minerals. Vegetables and grains are known to reduce the risk of heart disease.

• Some nutritional supplements provide vitamins and minerals that are missing from a person’s diet. These types of nutritional supplements contain important nutrients that reduce the risk of malnutrition.

• Consuming enzymes specific for carbohydrate digestion helps the body digest complex carbohydrates more quickly in the stomach and small intestine.

• Some nutritional supplements add beneficial bacteria to a person’s diet. These bacteria populate the stomach and prevent carbohydrate digestion.

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The diagram represents one way an enzyme can be inhibited. Which statement explains the effect of an inhibitor on an enzyme?

• A substrate will be able to bond with the enzyme.

• The enzyme will likely be attacked by immune cells.

• The enzyme will be unable to produce more enzymes.

• A substrate will be unable to attach to the enzyme.

People who have Alzheimer’s disease experience an increasing loss of brain function and cognition over time. Alzheimer’s is characterized by a buildup of abnormal protein fragments that damage brain cells. Recently scientists have discovered an enzyme, BACE2, that decreases these abnormal protein fragments in the brain of a person with Alzheimer’s disease. Which statement explains how BACE2 most likely works?

• BACE2 breaks down into smaller pieces that react with the abnormal protein fragments, forming more complex molecules.

• BACE2 speeds up the reaction that breaks down the abnormal protein fragments.

• BACE2 molecules link several abnormal protein fragments together, forming a complete protein.

• BACE2 is a reactant that combines with the abnormal protein fragments.

Fireflies emit light. The production of light by an organism is called bioluminescence. To generate visible light, cells in a firefly’s tail produce thousands of luciferase enzymes. Luciferase binds to a chemical called luciferin. Once bound, the luciferase enzyme speeds up a chemical reaction that combines an oxygen molecule and luciferin to produce oxyluciferin. This reaction requires energy and releases light. Which of the following best describes how the luciferase enzyme speeds up the chemical reaction?

• Luciferase increases the amount of time the light is visible.

• Luciferase decreases the amount of energy required for the reaction to start.

• Luciferase increases the number of sites on luciferin that must bind to oxygen.

• Luciferase decreases the temperature of the environment inside the body of the firefly.