Question 1

High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. This is an example of ________.

Accepted Answer

The fact that citric acid binds to the enzyme at a different location from the active site suggests that it is an allosteric regulator, rather than a competitive inhibitor, which would bind to the active site. The mention of "key enzyme" and "glycolysis" also suggest that this is a regulatory mechanism rather than a specificity issue or positive feedback.

Question 2

Which of the following metabolic processes take place in the cytosol of a eukaryotic cell?

Accepted Answer

Glycolysis and fermentation both occur in the cytosol of eukaryotic cells, while oxidation of pyruvate to acetyl CoA and the citric acid cycle occur in the mitochondria. Chemiosmosis is a part of oxidative phosphorylation, which occurs in the inner membrane of the mitochondria.

Question 3

The enzyme phosphofructokinase (PFK) catalyses a key step in glycolysis. PFK is inhibited by high levels of which of the following molecules?

Accepted Answer

ATP and citrate are both high energy molecules that signal to the cell that there is already enough energy available, and that more glucose should not be broken down for further energy production. Therefore, they inhibit the enzyme PFK in order to regulate glycolysis. Glucose and NAD+ are not inhibitors of PFK, and AMP and ATP are both involved in regulating glycolysis, but in opposite ways (AMP promotes glycolysis while ATP inhibits it), so they cannot both be inhibitors of PFK. Similarly, citrate and CO₂ are both products of the TCA cycle and do not play a direct role in regulating glycolysis.

Question 4

Which of the following metabolic processes normally occurs regardless of whether or not oxygen (O₂) is present?

Accepted Answer

The answer of Which of the following metabolic processes normally...

Question 5

In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve?

Accepted Answer

The increased surface area of the inner mitochondrial membranes in liver cells allows for an increased surface area for oxidative phosphorylation, the process by which ATP is generated from the electron transport chain. This process occurs on the inner mitochondrial membrane, so the increased surface area allows for a higher rate of ATP production.

Question 6

Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolising which of the following carbon sources for energy?

Accepted Answer

Yeast cells with defective mitochondria cannot carry out oxidative phosphorylation to generate ATP from glucose. However, they can still use glucose as a source of carbon and energy through glycolysis, which does not require functional mitochondria. Therefore, of the options given, glucose is the only suitable carbon source for growth of these yeast cells. Cholesterol, fatty acids, and amino acids require functional mitochondria for metabolism and ATP production.

Question 7

A person on a strict diet and exercise regimen lost 7 kg (about 15 pounds) of body fat in just two weeks. What is the most likely way that the lost fat left the body?

Accepted Answer

When the body breaks down fat molecules for energy, it ultimately releases the carbon atoms as CO₂, which is then exhaled, and the hydrogen atoms bond with oxygen to form water (H₂O), which is excreted through urine, sweat, and breath. Therefore, it is most likely that the lost fat left the body as CO₂ and H₂O.

Question 8

What kinds of cells carry out ATP synthesis by chemiosmosis?

Accepted Answer

All respiring cells, whether prokaryotic or eukaryotic, use ATP synthesis by chemiosmosis. This process occurs in the cell membrane of prokaryotes or in the inner mitochondrial membrane of eukaryotes. Both oxygen and other electron acceptors can be used in this process. Therefore, Option D is the most comprehensive and accurate choice.

Question 9

An organism is discovered that thrives in both the presence and absence of oxygen. Interestingly, as oxygen is removed from the organism's environment, the rate of sugar consumption increases while the growth rate decreases. What do these observations suggest about the likely identity of this organism?

Accepted Answer

The fact that this organism can thrive in both the presence and absence of oxygen suggests that it is a facultative anaerobic organism. The increase in sugar consumption and decrease in growth rate when oxygen is removed suggests that this organism can use both aerobic and anaerobic respiration, but prefers aerobic respiration when oxygen is available. This is characteristic of facultative anaerobes.

Question 10

What is the oxidising agent in the following reaction?
Pyruvate + NADH + H⁺ → Lactate + NAD⁺

Accepted Answer

The answer of What is the oxidising agent in the...

Question 11

Fatty acids usually have an even number of carbons in their structures. Catabolism of fatty acids produces two-carbon fragments that are converted to acetyl CoA molecules. What is the most likely way in which these acetyl CoA molecules would be metabolised in aerobic cellular respiration?

Accepted Answer

Acetyl CoA is the molecule that enters the citric acid cycle. This is the most likely way in which these acetyl CoA molecules would be metabolized in aerobic cellular respiration. The citric acid cycle produces electron carriers that then enter the electron transport chain, which generates ATP. Therefore, option A is incorrect. Acetyl CoA cannot directly enter the energy-yielding phase of glycolysis, making option B wrong. While it is possible for pyruvate to be converted to acetyl CoA, it is not the usual way it occurs. Hence, option C is also incorrect.

Question 12

A young dog has never had much energy. He is brought to a veterinarian for help, and she decides to conduct several diagnostic tests. She discovers that the dog's mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of the dog's condition?

Accepted Answer

The dog's mitochondria cannot use pyruvate because the transport protein needed to move pyruvate into the mitochondria is missing, leading to increased lactate production.

Question 13

Which of the following statements describes a primary function of both alcohol fermentation and lactic acid fermentation?

Accepted Answer

The answer of Which of the following statements describes a...

Question 14

The enzyme phosphofructokinase (PFK) catalyses a key step in glycolysis. About 10% of Springer spaniels suffer from canine PFK deficiency. Given its critical role in glycolysis, which of the following conditions would be a likely consequence for dogs afflicted with this disorder?

Accepted Answer

Canine PFK deficiency would result in a decreased ability to generate ATP through glycolysis. This means that affected dogs would have difficulty meeting their energy demands during exercise, resulting in lethargy and fatigue. Elevated blood-glucose levels (option B) are not expected since PFK deficiency would lead to decreased glucose metabolism. Option A is incorrect since PFK is not required for embryonic development, and option D is unlikely since glycolysis would be impaired, leading to decreased energy production overall.

Question 15

Why is glycolysis considered to be one of the first metabolic pathways to have evolved?

Accepted Answer

Glycolysis is considered to be one of the first metabolic pathways to have evolved because it is a simple pathway that does not involve organelles or specialised structures, does not require oxygen, and is present in most organisms, including prokaryotes and eukaryotes. This suggests that glycolysis may have been present in the earliest forms of life and was able to persist and evolve over time due to its simplicity and adaptability.

Question 16

Even though plants cells carry out photosynthesis, they still use their mitochondria for oxidation of pyruvate. Under what conditions will plant cell mitochondria be active in this process?

Accepted Answer

Plant cell mitochondria are always active in oxidation of pyruvate, regardless of whether the cell is photosynthetic or not, and whether or not there is light. This is because oxidation of pyruvate is necessary for the production of ATP through cellular respiration, which is essential for the cell's energy needs.

Question 17

In the absence of oxygen, yeast cells can obtain energy by fermentation, which results in the production of which of the following sets of molecules?

Accepted Answer

In the absence of oxygen, yeast cells undergo alcoholic fermentation, which produces ATP, carbon dioxide (CO₂), and ethanol (ethyl alcohol) as the end products.

Question 18

Exposing inner mitochondrial membranes to ultrasonic vibrations will disrupt the membranes. However, the fragments will reseal "inside out". The little vesicles that result can still transfer electrons from NADH to oxygen and synthesise ATP. Which of the following statements about these inside-out membrane vesicles is true?

Accepted Answer

The answer of Exposing inner mitochondrial membranes to ultrasonic vibrations...

Question 19

Beta oxidation generates substrates for cellular respiration through which of the following processes?

Accepted Answer

Beta oxidation is the catabolism of fatty acids, which generates substrates for cellular respiration in the form of acetyl-CoA, NADH, and FADH2.

Question 20

Exposing inner mitochondrial membranes to ultrasonic vibrations will disrupt the membranes. However, the fragments will reseal "inside out". The little vesicles that result can still transfer electrons from NADH to oxygen and synthesise ATP. After the disruption, which components involved in oxidative phosphorylation must be present for electron transfer and ATP synthesis to still occur?

Accepted Answer

Both the electron transport system and the ATP synthase system must be present for electron transfer and ATP synthesis to still occur. The disruption of inner mitochondrial membranes does not affect the proteins that add CoA to acetyl groups.

Quiz 9: Cellular Respiration and Fermentation