Chapter 8 and 9 Test

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students' results are shown in graph 1. pH If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

lower than the level at pH 9

Which of the following describes a metabolic consequence of a shortage of oxygen in muscle cells?

A buildup of lactic acid in the muscle tissue due to fermentation

A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (Pi) is essential to cellular function.

ATP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy.

Butterflies of the genus Colias live in the Rocky Mountains, where they experience a wide range of temperatures. Different variants of a particular glycolytic enzyme in the flight muscles are optimally active at different temperatures. Within the same population, some individual butterflies fly most effectively at 29°C , while others fly most effectively at 40°C. Still others can be equally active at both temperatures. Which of the following claims is most consistent with the observed butterfly behavior?

Butterflies that express two variants of the enzyme are active over a greater range of temperature.

Which of the following statements about mitochondrial chemiosmosis is NOT true?

Heat energy is required to establish the electron transport chain.

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body. Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Coenzyme that transfers electrons from the Krebs cycle to the mitochondrial electron-transport chain at a lower energy level than that of electrons entering at the beginning of the chain

FADH2

Which metabolic process is common to both aerobic cellular respiration and alcoholic fermentation?

Glycolysis

For the following questions: Graphs I-IV depict the effect of pH on the activity of four different hydrolytic enzymes. Graphs representing enzymes sensitive to changes in pH include which of the following?

I, II, and III only

Which of the following questions will best direct an investigation of the mechanism of ATP synthase?

Is the phosphorylation of ADP by ATP synthase dependent on the formation of a proton gradient?

Amylase is a protein that catalyzes the conversion of starch to simple sugars. Amylase activity in an aqueous solution can be measured by using iodine as a starch indicator. A solution containing iodine and starch will have a dark-blue color, whereas a solution containing iodine but no starch will have a light-brown color. The color change of an iodine solution from dark blue to light brown can be used to measure the rate at which starch is converted to simple sugars. A student designs an experiment to investigate the effect of environmental pH on amylase function. The design of the experiment is presented in Table 1. Which of the following statements best justifies the inclusion of test tube V as a control in the experiment?

It will show the color change that occurs in the absence of enzyme activity.

An intermediate electron acceptor for oxidations that occur in both glycolysis and in Krebs cycle reactions

NAD+

Protein digestion in humans is primarily carried out by three enzymes. Pepsin is found in the stomach (pH2), where it aids in the breakdown of large proteins into smaller peptides, while trypsin and chymotrypsin are found in the small intestine (pH8), where they aid in the further breakdown of the proteins into amino acids and dipeptides that can be absorbed into the bloodstream. Graph 1 shows the effect of pH on the activity levels of the three enzymes. pH Which of the following best predicts how the structure and function of pepsin will change as it enters the small intestine?

Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease.

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product.

The enzyme's active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.

The figure above shows an organelle typically found in eukaryotic cells. Which of the following best describes the function of the double membrane system of this organelle?

The inner membrane has specialized proteins that create a hydrogen ion concentration gradient between the intermembrane space and the matrix.

Two nutrient solutions are maintained at the same pH. Actively respiring mitochondria are isolated and placed into each of the two solutions. Oxygen gas is bubbled into one solution. The other solution is depleted of available oxygen. Which of the following best explains why ATP production is greater in the tube with oxygen than in the tube without oxygen?

The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen.

Which of the following statements best helps explain the reaction specificity of an enzyme?

The shape and charge of the substrates are compatible with the active site of the enzyme.

Which of the following best describes the function of the coenzymes NAD+ and FAD in eukaryotic cellular respiration?

They accept electrons during oxidation-reduction reactions.

The reactions of glycolysis occur in the

cytosol

According to the chemiosmotic theory (chemiosmotic coupling), the energy required to move protons from the mitochondrial matrix to the intermembrane space against a concentration gradient comes most directly from

electrons flowing along the electron transport chain

Within the cell, many chemical reactions that, by themselves, require energy input (have a positive free-energy change) can occur because the reactions

may be coupled to the hydrolysis of ATP

When hydrogen ions are pumped out of the mitochondrial matrix, across the inner mitochondrial membrane, and into the space between the inner and outer membranes, the result is

the creation of a proton gradient