Exam 8: An Introduction to Metabolism

In order to attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an aminoacyl-tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur in order for the final attachment to occur?

The following questions are based on the reaction A + B ↔ C + D shown in Figure 8.1. Figure 8.1 -Which of the following represents the activation energy required for a noncatalyzed reaction in Figure 8.1?

In experimental tests of enzyme evolution, where a gene encoding an enzyme is subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity, the resulting enzyme had multiple amino acid changes associated with altered substrate specificity. Where in the enzyme were these amino acid changes located?

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?

Chemical equilibrium is relatively rare in living cells. Which of the following could be an example of a reaction at chemical equilibrium in a cell?

A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. -With respect to the enzyme that converts X to Y, substance A functions as

Activity of various enzymes at various temperatures (a) and at various pH (b). -Which curve(s)on the graphs may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher?

The following questions are from the end-of-chapter "Test Your Understanding" section in Chapter 8 of the textbook. -Which of the following metabolic processes can occur without a net influx of energy from some other process?

How might an amino acid change at a site distant from the active site of the enzyme alter the enzyme's substrate specificity?

The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are)correct?

The following questions are based on the reaction A + B ↔ C + D shown in Figure 8.1. Figure 8.1 -Which of the following represents the difference between the free-energy content of the reaction and the free-energy content of the products in Figure 8.1?

The following questions are from the end-of-chapter "Test Your Understanding" section in Chapter 8 of the textbook. -Most cells cannot harness heat to perform work because

Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. -Based on this information, which of the following is correct?

The following questions are based on the reaction A + B ↔ C + D shown in Figure 8.1. Figure 8.1 -Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in Figure 8.1?

Which of the following is an example of potential rather than kinetic energy?

Which of the following is an example of cooperativity?

Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?

Which of the following statements is true concerning catabolic pathways?

An important group of peripheral membrane proteins are enzymes such as the phospholipases that cleave the head groups of phospholipids. What properties must these enzymes exhibit?

When 10,000 molecules of ATP are hydrolyzed to ADP and ᵢin a test tube, about twice as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?