English Quiz

Question 1

Which cell in the human body only uses glycolysis for ATP production?

Possible Answers:
Erythrocyte

Hepatocyte

Myocyte

Neuron

Answer 1

Erythrocyte

Explanation:
Erythrocytes (red blood cells) have no mitochondria, and thus cannot use oxidative phosphorylation to produce additional ATP from pyruvate derived from glycolysis.

Liver cells (hepatocytes), neurons, and muscle cells (myocytes) can derive some ATP from glycolysis, but then feed the resulting pyruvate into the Krebs cycle in the mitochondria for additional energy production.

Question 2

Which of the following biological processes will occur under both aerobic and anaerobic conditions in humans?

Possible Answers:
Krebs cycle

Fermentation

All of the these processes occur in both environments

Citric acid cycle

Glycolysis

Answer 2

Glycolysis

Explanation:
The correct answer is glycolysis. Fermentation is a pathway that requires anaerobic conditions to activate. The citric acid cycle and Krebs cycle are two terms for the same process, and require aerobic conditions to proceed. Glycolysis has pathways that account for situations both in the presence and absence of oxygen.

Question 3

Which statement about glycolysis is correct?

Possible Answers:
Resulting pyruvate molecules are always directly incorporated into the Krebs cycle

Two net molecules of ATP are produced through substrate-level phosphorylation

Glycolysis cannot proceed under anaerobic conditions

Three molecules of NADH2 and one molecule of FADH2 are produced

A proton gradient is established across the mitochondrial membrane

Answer 3

Two net molecules of ATP are produced through substrate-level phosphorylation

Explanation:
In glycolysis, four ATP molecules made from each unit of glucose, however, two ATP molecules are used during this process, so the net result of one round of glycolysis is two ATP molecules. These products are made via substrate-level phosphorylation, a process in which a phosphorylated molecule transfers its phosphate to ADP or GDP (producing ATP or GTP).

The other choices are incorrect. Three NADH2 and one FADH2 are made in one round of the Krebs cycle, not glycolysis. Glycolysis is an anaerobic process and takes place in the cytoplasm, not the mitochondria. Finally, pyruvate products do not necessarily have to enter the Krebs cycle—they can be metabolized anaerobically if insufficient oxygen is present.

Question 4

Which of the following is a product of glycolysis?

Possible Answers:
O2

Acetyl CoA

GTP

Glucose

NADH

Answer 4

NADH

Explanation:
In glycolysis, one glucose molecule and two NAD+ molecules yield two molecules of pyruvate, two molecules of ATP, and two molecules of NADH.

Acetyl CoA is formed from pyruvate at the beginning fo the Krebs cycle. GTP is a product of the Krebs cycle. Oxygen and glucose are both reactants in metabolic processes that are derived from external intake (respiration and digestion).

Question 5

Given the process of glycolysis, which of the following would serve to allosterically inhibit the rate of glycolysis?

Possible Answers:
Increased fructose

Increased glucose

Increased ATP

Decreased ATP

Increased oxygen

Answer 5

Increased ATP

Explanation:
The product of glycolysis is ATP, and each cycle gives a net of two ATP, thus if there were already high levels of ATP in the body, glycolysis would not have to occur as frequently since the body’s energy demands are already being met. High levels of ATP would serve as an allosteric inhibitor.

Decreased ATP and increased glucose would increase the rate of glycolysis. Increased oxygen or fructose may indirectly increase the rate of glycolysis, depending on other cellular factors.

Question 6

Which of the following products is not created by glycolysis?

Possible Answers:
Pyruvate

Lactic acid

ATP

NADH

Answer 6

Lactic acid

Explanation:
Glycolysis is the first step of cellular respiration. It is responsible for the production of two ATP molecules, two pyruvate molecules, and two NADH molecules. Lactic acid is a byproduct of anaerobic respiration in skeletal muscle.

Question 7

What is the location of glycolysis?

Possible Answers:
The cytosol

The intermembrane space

The outer mitochondrial membrane

The mitochondrial matrix

Answer 7

The cytosol

Explanation:
The first step of respiration is glycolysis. All of the steps of glycolysis take place in the cytosol of the cell; this allows prykarotes to perform glycolysis, as well as eukaryotes.

Once pyruvate is generated from glycolysis, it is transported to the mitochondria to complete the citric acid cycle. The electron transport chain, the final step of cellular respiration, is located on the inner mitochondrial membrane, and utilizes the proton gradient in the intermembrane space.

Question 8

Which of the following is not true of glycolysis?

Possible Answers:
It produces NADH

It requires an input of ATP to begin

It occurs in the cytoplasm

It produces four net ATP

It is anaerobic

Answer 8

It produces four net ATP

Explanation:
Glycolysis produces four total ATP molecules, but only produces two net ATP. The process requires an initial investment of two ATP to initiate the glycolysis pathway. By using two ATP and producing four, there is a net production of two ATP.

Glycolysis is an anaerobic process that occurs in the cytoplasm. In addition to making ATP, glycolysis also generates NADH, which goes to play a role in the electron transport chain.

Question 9

Which of the following is not a product in the net reaction for glycolysis?

Possible Answers:
Water

NADH

ATP

Pyruvate

ADP

Answer 9

ADP

Explanation:
The glycolysis reaction follows two step. The initiation requires the input of two ATP, which become converted to ADP. Later in the process, however, four ADP are required to produce four ATP products. ADP is consumed in a greater quantity than it is produced, eliminating it from the net products.

Glucose+2ADP+2NAD+→2Pyruvate+2ATP+2NADH+2H2O

Question 10

What type of enzyme is responsible for initiating the process of glycolysis?

Possible Answers:
Kinase

Hydrolase

Phosphorylase

Phosphotase

Answer 10

Kinase

Explanation:
The initial reactants for glycolysis are glucose, ATP, ADP, and NAD+. The final products are pyruvate, ATP, ADP, and NADH. To get from glucose to pyruvate, a number of enzymes are needed. While knowing the names of each enzyme is not usually necessary, it is important to have a general understanding of the glycolytic process. The first step is phosphorylation of the reactant glucose, which is accomplished by hexokinase in most cells, and by glucokinase in the liver and pancreas specifically. The resultant glucose-6-phosphate then continues through the remaining steps in glycolysis to produce pyruvate.

Question 11

Which of the following does not occur in the mitochondrion?

Possible Answers:
Citric acid cycle

Pyruvate dehydrogenase complex

Oxidative phosphorylation

Krebs Cycle

Glycolysis

Answer 11

Glycolysis

Explanation:
Glycolysis is the only metabolic process of the choices listed that does not occur in the mitochondrion; it occurs in the cytoplasm. Citric acid cycle and Krebs cycle refer to the same process, which occurs in the mitochondrion.

Question 12

For eukaryotes, the total yield of ATP from NADH is not always maximized when the NADH is manufactured by which of the following?

Possible Answers:
Glycolysis

Pyruvate dehydrogenase complex

Electron transport and oxidative phosphorylation

Fermentation

Citric acid cycle

Answer 12

Glycolysis

Explanation:
For the NADH produced during glycolysis to be used in the electron transport chain (ETC), the electrons have to be sent into the inner membrane of the mitochondria from the cytoplasm, since glycolysis takes place in the cytoplasm. When the NADH is sent inside, sometimes it skips over NADH dehydrogenase and goes directly to coenzyme Q. The NADH does not always skip over NADH dehydrogenase, but it depends on the shuttle it takes into the mitochondrial matrix. The two shuttles are malate-aspartate, which maximizes NADH’s ATP production, and glycerol-3-phosphate, which oxidizes one molecule of NADH, resulting in a decrease in the number of protons pumped. The type of shuttle depends on the cell type. This results in fewer protons being pumped out of the mitochondrial matrix, and thus fewer ATP being formed.

Question 13

Within the Krebs cycle, L-malate and NAD+ come together to form oxaloacetate, NADH, and H+. What type of chemical reaction is responsible for this step in the cycle?

Possible Answers:
Decarboxylation

Oxidation

Dehydration

Hydration

Answer 13

Oxidation

Explanation:
In order for oxaloacetate to be formed, malate must lose electrons, which is the definition of an oxidation reaction. Alternately, NAD+ is reduced (gains electrons) to form NADH and H+.

Question 14

During cellular respiration, where is NADH produced?

Possible Answers:
The nucleus

The endoplasmic reticulum

The mitochondrial intermembrane space

The cytosol

The cytosol and mitochondrial matrix

Answer 14

The cytosol and mitochondrial matrix

Explanation:
NADH is produced during glycolysis, which occurs in the cytoplasm. NADH is also produced during the Krebs cycle, which occurs in the mitochondrial matrix. The protons generated in the production of NADH are later used in the intermembrane space to power ATP synthase during oxidative phosphorylation.

Question 15

If the Krebs cycle is overstimulated, the body will produce too much of which of the following molecules?

Possible Answers:
Acetyl CoA

Glucose

Carbon dioxide

Oxygen

Pyruvate

Answer 15

Carbon dioxide

Explanation:
Of the answer choices, only carbon dioxide is a product of the Krebs cycle. If the cycle is overstimulated, too much of the products will be formed and the body will have too much carbon dioxide.

Glucose is the reactant that fuels glycolysis to produce pyruvate, which is then converted to acetyl CoA for the Krebs cycle. As such, each of these would be depleted as reactants fueling an overstimulation of the Krebs cycle.

Question 16

Where is the Krebs cycle carried out in eukaryotic cells?

Possible Answers:
Cytosol

Nucleus

Inner membrane of the mitochondria

Mitochondrial matrix

Answer 16

Mitochondrial matrix

Explanation:
During the Krebs cycle, or citric acid cycle, acetyl CoA is oxidized to CO2 and NAD+ and FADH are reduced to NADH and FADH2, respectively. This process is carried out in the mitochondrial matrix of eukaryotic cells.

The electron transport chain is carried out in the inner membrane of the mitochondria, while glycolysis is carried out in the cytosol.

Question 17

Cellular respiration is the set of metabolic reactions that occur in cells to produce energy in the form of ATP. During cellular respiration, high energy intermediates are created that can then be oxidized to make ATP. During what stage are these intermediates produced?

Possible Answers:
Oxidative phosphorylation and the citric acid cycle

The citric acid cycle

The citric acid cycle and glycolysis

Oxidative phosphorylation

Glycolysis

Answer 17

The citric acid cycle and glycolysis

Explanation:
The citric acid (Krebs) cycle and glycolysis yield high energy intermediates that can then be used to make ATP. Each turn of the citric acid cycle generates NADH and FADH2, and each cycle of glycolysis generates NADH. These intermediates can then donate their electrons and become oxidized in the electron transport chain. Production of these electron donors is essential to the function of the electron transport chain.

Question 18

Acetyl-CoA is a react in the citric acid cycle, while NADH and FADH2 are products. If twelve molecules of NADH are produced over a period of time, how many FADH2 molecules are produced during this period?

Possible Answers:
Twenty-four

Four

Twelve

Two

Answer 18

Four

Explanation:
Each turn of the citric acid cycle is powered by one molecule of acetyl-CoA, resulting in three NADH and one FADH2. The net reaction is:

Acetyl-CoA+3NAD++FAD+ADP+HPO−24→2CO2+CoA+3NADH+FADH2+ATP

Since twelve NADH are produced, there must have been an input of four acetyl-CoA molecules and four total turns in the cycle. As a result, four FADH2 molecules were produced.

Question 19

Which statement is false regarding the citric acid cycle?

Possible Answers:
It occurs in the mitochondrial matrix for eukaryotes

6 GTP molecules would be produced starting with 3 glucose molecules

All of these

Another name for it is the Krebs cycle

Oxygen is directly required for the citric acid cycle to occur

Answer 19

Oxygen is directly required for the citric acid cycle to occur

Explanation:
Oxygen is needed for the electron transport chain to occur which oxidizes NADH and FADH2. If there is no oxygen available then Krebs cycle would not occur since there would be no oxidized electron carriers. Therefore oxygen is only indirectly required for the Krebs cycle to occur, not directly.

Question 20

James took a neural sample and separated the cell body from the axon. He noticed that when he placed both parts on a glucose plate, the cell body began releasing carbon dioxide. What could explain the result?

Possible Answers:
The carbon dioxide came from the plate

None of these

The cell body is degrading

The cell body contains mitochondria

The carbon dioxide is used as a messenger to communicate with the axon

Answer 20

The cell body contains mitochondria

Explanation:
The cell body of a neuron is where the mitochondria and all other organelles are located. Recall from the Krebs cycle that carbon dioxide is produced as a byproduct. Anaerobic respiration, which occurs in the cytoplasm does not release carbon dioxide (in humans) and produces lactic acid instead. Note that in certain organisms like yeast, fermentation produces ethanol (two-carbons) and carbon dioxide since pyruvate, the product of glycolysis is a three-carbon molecule.

Question 21

The drug, DNP, destroys the H+ gradient that forms in the electron transport chain. What is the most likely consequence?

Possible Answers:
Glycolysis will stop.

Oxygen consumption will increase.

No effect will occur.

The cells will be forced to perform fermentation.

ATP production will increase.

Answer 21

The cells will be forced to perform fermentation.

Explanation:
If the proton gradient of the electron transport chain were to be destroyed, the cell would need to perform cellular respiration without an electron transport chain. The only option would be to move to anaerobic respiration, which requires fermentation.

Question 22

Given a healthy individual with a normal metabolic rate, which of the following compounds is the most energy rich?

Possible Answers:
FADH2

GTP

ATP

NADH

Answer 22

NADH

Explanation:
This question is asking about ATP production during cellular respiration. During oxidative phosphorylation (the electron transport chain), each 1 ATP is produced for each GTP, 2 ATP are produced for each FADH2, and 3 ATP are produced for each NADH.

Question 23

A person is born with a mutation that causes their cells to not have the ability to produce the NADH dehydrogenase complex, the complex that allows the electron transport chain to make ATP from NADH. Will this patient be able to produce any enery at all from the ETC?

Possible Answers:
No—there are no other molecules the ETC uses.

Yes—NAD+ can still enter the ETC.

No—NADH is necessary for the ETC to use other molecules to make ATP.

Yes—FADH2 can still enter the ETC.

No—FAD can still enter the ETC.

Answer 23

Yes—FADH2 can still enter the ETC.

Explanation:
FADH2 enters the ETC at the succinate-Q oxidoreductase complex. While this doesn’t generate as much energy as NADH will because the electrons travel a shorter distance, there are still 2 ATP molecules made for each FADH2.

Question 24

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

Cancer cells require large amounts of energy in the form of ATP. Which of the following processes results in the greatest production of ATP?

Possible Answers:
Oxidative phosphorylation

Fermentation

Substrate-level phosphorylation

The Krebs cycle

Glycolysis

Answer 24

Oxidative phosphorylation

Explanation:
Oxidative phosphorylation in the mitochondria is the major contributor to the total ATP pool in most eukaryotic cells. Keep in mind that it is oxidative phosphorylation in concert with the proton gradient that drives the electron transport chain.

Question 25

A new treatment for bladder cancer is developed that targets energy production in malignant cells. Which of the following potential target sites would directly involve the synthesis of most of the ATP in a cell?

Possible Answers:
ATP synthase, an enzyme housed on the inner mitochondrial membrane

Lactate dehydrogenase, an enzyme in the cytosol

Ribosomes

ATP synthase, an enzyme housed in the mitochondrial matrix

ATP synthase, an enzyme housed on the outer mitochondrial membrane

Answer 25

ATP synthase, an enzyme housed on the inner mitochondrial membrane

Explanation:
ATP synthase is housed on the inner mitochondrial membrane, and is the main ATP production agent in oxidative phosphorylation. It provides a channel for protons to enter the matrix from the intermembrane space, and in so doing, drives ATP production.

Question 26

What phase of cellular respiration has the highest ATP yield?

Possible Answers:
Glycolysis

Fermentation

Gluconeogenesis

Krebs cycle

Oxidative phosphorylation

Answer 26

Oxidative phosphorylation

Explanation:
Oxidative phosphorylation, which traps energy in a high-energy phosphate bond and uses an electron gradient and ATP synthase to create ATP, yields the most ATP. Oxidative phosphorylation is linked with the electron transport chain.

Glycolysis only gives a net of two ATP per glucose, and the Krebs cycle gives two GTP for every turn of the cycle. Gluconeogenesis is not a part of cellular respiration, and fermentation is very low-yield since it occurs in the absence of oxygen.

Question 27

Why is oxygen necessary in aerobic cellular respiration?

Possible Answers:
It is needed for glycolysis, which begins the process of respiration in cells.

It is important in creating oxaloacetic acid in the Kreb’s cycle.

It provides the hydrogen nuclei needed to create a proton gradient in the intermemberane space.

It is the final electron acceptor in the electron transport chain.

Answer 27

It is the final electron acceptor in the electron transport chain.

Explanation:
Oxygen is the final electron acceptor in the electron transport chain, which results in the production of water. Glycolysis does not require oxygen, and can be done in anaerobic environments. NADH is the molecule which is oxidized in order to establish the proton gradient. Finally, oxygen is not needed to create oxaloacetic acid is the Kreb’s cycle, as it is regenerated after each turn of the cycle.

Question 28

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

One of the main arguments in favor of the theory of endosymbiosis is that mitochondria have their own genome. Which of the following cellular structures is most likely to be coded for only by mitochondrial DNA?

Possible Answers:
Electron transport chain proteins

Glycolytic enzymes

Insulin-like growth factor 1

Sodium-potassium ATPase

Growth hormone

Answer 28

Electron transport chain proteins

Explanation:
Electron transport chain (ETC) proteins are encoded by the the mitochondrial DNA. This makes sense, as we find ETC proteins only in the mitochondrial membrane (remember, as the passage states, aerobic metabolism is limited to the mitochondria).

It may be tempting to select glycolytic enzymes, as the free living predecessors to mitochondria presumably underwent glycolysis; however, these genes have been lost as the symbiosis matured and glycolysis was localized to the cellular cytosol.

Question 29

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

With regard to the energy production by the mitochondria discussed in the passage, what is the main factor driving ATP production at the terminal step of aerobic metabolism?

Possible Answers:
The reduction of glucose to lactate

The oxidation of glucose to lactate

The oxidation of glucose to pyruvate

Energy from the electrochemical proton gradient is captured by ATP synthase

The reduction of glucose to pyruvate

Answer 29

Energy from the electrochemical proton gradient is captured by ATP synthase

Explanation:
The final step in aerobic metabolism is the capture of the stored energy of protons existing in the intermembrane space. The electrochemical gradient in the intermembrane space forces protons through ATP synthase, phosphorylating ADP.

Glucose is converted to pyruvate during glycolysis, and to lactate during anaerobic respiration.

Question 30

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

The primary purpose of the electron transport chain of mitochondria described in the passage is __________.

Possible Answers:
to synthesize ATP synthase

to carry ADP into the mitochondrial matrix

to directly phosphorylate AMP

to directly phosphorylate ADP

the generation of energy to sequester protons in the intermembrane space

Answer 30

the generation of energy to sequester protons in the intermembrane space

Explanation:
The electron transport chain serves to pump protons into the intermembrane space. The result is the buildup of the electrochemical gradient, and the passage of protons through ATP synthase. Essentially, the electron transport chain establishes the conditions for oxidative phosphorylation to occur.

Question 31

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

A scientist is studying typical mitochondria as described in the passage. In the course of his study, he measures the generation of NADH and FADH2. What is the normal destination of NADH and FADH2?

Possible Answers:
Pyruvate dehydrogenase

Electron transport chain proteins

The mitochondrial matrix

ATP synthase

The intermembrane space

Answer 31

Electron transport chain proteins

Explanation:
NADH and FADH2 are electron carriers. They bring electrons from their production point (glycolysis or the Kreb’s cycle) to the electron transport chain proteins. The electrons are then passed down the electron transport chain to generate energy.

Question 32

Which of the following areas of the mitochondria has the lowest pH?

Possible Answers:
The mitochondrial christae

The cytosol

The intermembrane space

The mitochondrial matrix

Answer 32

The intermembrane space

Explanation:
ATP synthase, which is located on the inner mitochondrial membrane, requires a proton gradient in order to create ATP. This means that the protons need to be pumped across the inner mitochondrial membrane into the intermembrane space. This results in the intermembrane space having the lowest pH in the mitochondria, due to the high proton concentration.

The mitochondrial matrix is the interior of the inner mitochondrial membrane, while the cytosol is not a part of the mitochondria. Neither of these have particularly low pH values. Christae are the folds of the inner mitochondrial membrane that increase its surface area for the electron transport chain processes; though structurally useful in facilitating respiration, the pH of christae is roughly the same as that of the mitochondrial matrix.

Question 33

During aerobic respiration, which of the following pathways correctly orders the process of cellular metabolism after glycolysis in eukaryotic cells?

Possible Answers:
Citric acid cycle → Pyruvate decarboxylation → Oxidative phosphorylation

Pyruvate decarboxylation → Oxidative phosphorylation → Citric acid cycle

Citric acid cycle → Oxidative phosphorylation → Pyruvate decarboxylation

Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation

Answer 33

Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation

Explanation:
After glycolysis is complete, we have generated pyruvate from glucose. We would then expect pyruvate decarboxylation to be the first step after glycolysis in aerobic respiration. When pyruvate is decarboxylated, we generate acetyl CoA, which fuels the Krebs cycle (aka TCA, and citric acid cycle). We would expect the next step after decarboxylation to be the citric acid cycle. In the citric acid cycle we generate FADH2 and NADH, which release free energy in oxidative phosphorylation to generate the proton gradient across the mitochondrial membrane to fuel ATP synthase.

Question 34

A deficiency in which of the following within the mitochondrial matrix will not limit a cell’s rate of oxidative phosphorylation?

Possible Answers:
NAD+

A deficiency in any of these will limit the rate of oxidative phosphorylation

FADH2

O2

Answer 34

A deficiency in any of these will limit the rate of oxidative phosphorylation

Explanation:
Oxidative phosphorylation is dependent on the functionality of the electron transport chain. In the electron transport chain, NADH and FADH2 act as electron donors. The donated electrons are used by protein complexes along the inner mitochondrial membrane to establish the proton gradient in the intermembrane space. Once the electrons have passed through the complexes, they are donated to an oxygen molecule to create water. Oxygen is the final electron acceptor in the chain, and is essential for oxidative phosphorylation to occur.

NAD+ is the precursor of NADH, making it another crucial molecule for cell metabolism. NAD+ is converted to NADH during glycolysis and the Krebs cycle. A deficiency of NAD+ in the mitochondrial matrix will slow the Krebs cycle, which will turn slow oxidative phosphorylation.

Question 35

Which of these processes in aerobic respiration would not be possible in the absence of oxygen?

Possible Answers:
The Krebs cycle

Glycolysis

The electron transport chain

Formation of NADH from NAD+

Substrate-level phosphorylation

Answer 35

The electron transport chain

Explanation:
Oxygen is necessary to be the last electron acceptor in the electron transport chain. This results in the formation of water.

Oxygen is not involved in glycolysis, which utilizes substrate-level phosphorylation, nor is it needed for the Krebs cycle. NAD+ is converted to NADH during glycolysis and the Krebs cycle without involving oxygen.

Question 36

Which of these are examples of passive transport?
I. Simple diffusion
II. Voltage-gated channels
III. Channel proteins
IV. Proton pump
Possible Answers:
I only

I and II

I, II, and III

I, II, III, and IV

II and IV

Answer 36

I, II, and III

Explanation:
The two main classifications for transport are active transport and passive transport. Active transport requires the conversion of ATP to ADP, and generally involves pumping molecules against their concentration gradients. Passive transport, in contrast, does not require the use of cellular energy.

Any form of diffusion, either simple diffusion through a membrane or facilitated diffusion via a channel protein, qualifies as passive transport and does not require ATP mediation. Similarly, voltage-gated channels require a certain electrical environment to mediate their function, but do not require the presence of ATP. Proton pumps act to push protons against their concentration gradient, and require the input of cellular energy, thus qualifying as active transport.

Question 37

Imagine that a toxin is introduced to the body and inhibits the establishment of the proton gradient in the intermembrane space. What would you predict would be the result?

Possible Answers:
NADH would be oxidized

Substrate-level phosphorylation would be inhibited

ATP synthase would be unable to produce ATP

Pyruvate would be unable to enter the Krebs cycle

Fermentation could not occur

Answer 37

ATP synthase would be unable to produce ATP

Explanation:
ATP synthase is dependent on a proton gradient in the intermembrane space in order to produce ATP. As a result, the toxin will make it inactive. Oxidative phosphorylation would be inhibited in this case, as opposed to substrate-level phosphorylation.

Pyruvate is a product of glycolysis, and would not be affected by the toxin. NADH is key in the establishment of the proton gradient, so we would expect that it would be unable to be oxidized due to the toxin. Protons produced in the conversion of NADH to NAD+ (+H+) establish the proton gradient. If the gradient is absent, NADH is likely not be oxidized.

Question 38

When a certain bacterium undergoes aerobic respiration, which area would have the lowest pH?

Possible Answers:
Cytoplasm

Golgi body

Mitochondrial matrix

Extracellular

Nucleus

Answer 38

Extracellular

Explanation:
Bacteria are prokaryotes. Since prokaryotes do not have any membrane bound organelles, during respiration, protons are pumped from the cytoplasm to the extracellular region between the plasma membrane and the cell wall. This results in a gradient between those two regions, thus extracellular would have a lower pH.

Question 39

Cyanide is very toxic in high enough doses because it binds irreversibly to cytochrome C. Which of the following is not an effect of cyanide’s inhibition of cytochrome C?

Possible Answers:
Build up of NADH

Increase in the rate of the citric acid cycle’s activity

Increased pH in the mitochondrial intermembrane space

Increase in fermentation activity

Increased ratio of ADP:ATP

Answer 39

Increase in the rate of the citric acid cycle’s activity

Explanation:
The inhibition of cytochrome C means that the electron transport chain is no longer able to shuttle electrons from complex III to complex IV, which means it is no longer able to accept electrons from electron carriers. As a result, the citric acid cycle would slow down since there would be a build-up of NADH, which allosterically inhibits several enzymes in the citric acid cycle.

Since the electron transport chain no longer functions properly, there wouldn’t be as many H+ ions being pumped into the intermembrane space, which would increase the pH in the intermembrane space. Also, with the decline in the H+concentration, oxidative phosphorylation would no longer be efficient, and the cell would have to increase rate of fermentation to increase energy output.

Question 40

What is the purpose of the formation of lactic acid during anaerobic respiration?

Possible Answers:
It allows NAD+ to reform

It allows FADH2 to reform

It allows NADH to reform

It allows FAD to reform

It allows glucose to reform

Answer 40

It allows NAD+ to reform

Explanation:
Cells need a constant supply of NAD+ to accept electrons during glycolysis in order to produce pyruvate from glucose.

Question 41

Which statement is FALSE when comparing aerobic to anaerobic respiration?

Possible Answers:
Aerobic repsiration is responsible for the muscle pain felt during strenuous exercise.

Aerobic respiration creates more ATP from each glucose molecule used.

Both processes begin with glycolysis.

Both processes produce pyruvate.

Answer 41

Aerobic repsiration is responsible for the muscle pain felt during strenuous exercise.

Explanation:
Anaerobic respiration creates the byproduct lactic acid. Accumulation of lactic acid in the muscles due to lack of oxygen results in the pain we experience during exercise. Remember that aerobic respiration creates 36 ATP molecules per glucose, while anaerobic repiration forms only 2 ATP molecules per glucose. Since both processes begin with glycolysis, pyruvate is still generated.

Note that while lactic acid is responsible for the “burn” in muscles during exercise, other agents are responsible for muscle soreness after exercise.

Question 42

While running a marathon, an individual feels pain and a burning sensation in her legs. One reason for this is the conversion of pyruvate into lactic acid which the body does in order to __________.

Possible Answers:
regenerate NAD+ from NADH

regenerate FADH2 from FADH

regenerate FADH from FADH2

regenerate NADH from NAD+

Answer 42

regenerate NAD+ from NADH

Explanation:
In the absence of available oxygen, the body conducts metabolism anaerobically in a process known as fermentation. During strenuous exercise, like running a marathon, the body needs to generate ATP at a rate faster than oxygen is becoming available.

To combat this issue, the body converts pyruvate and NADH, generated in glycolysis, into lactic acid and NAD+, respectively. This regenerated NAD+ can participate in further glycolysis to generate more ATP, even in the absence of oxygen. Oxygen only becomes a necessary reactant in the electron transport chain; thus, glycolysis can continue to generate limited amounts of ATP in an anaerobic environment as long as NAD+ is present.

Question 43

Which choice accurately states the amount of ATP produced from a single glucose molecule in an anaerobic environment and in an aerobic environment, respectively?

Possible Answers:
Anaerobic respiration produces 34 ATP; aerobic respiration produces 2

Anaerobic respiration produces 4 ATP; aerobic respiration produces 8 ATP

Anaerobic respiration produces 2 ATP; aerobic respiration produces 36 ATP

Anaerobic respiration produces 40 ATP; aerobic respiration produces 4 ATP

Anaerobic respiration produces 2 ATP; aerobic respiration produces 2 ATP

Answer 43

Anaerobic respiration produces 2 ATP; aerobic respiration produces 36 ATP

Explanation:
In an anaerobic environment, two net ATP are produced from glycolysis. Since glycolysis requires an investment of two ATP and produces four ATP, it has a total net yield of two ATP. In an aerobic environment, however, the cell performs glycolysis, pyruvate decarboxylation, the citric acid cycle, and oxidative phosphorylation. These processes together yield a net of 36 ATP.

Question 44

What is the purpose of fermentation?

Possible Answers:
To generate NAD+

To generate ATP

To oxidize pyruvate

To generate carbon dioxide

To produce disaccharides

Answer 44

To generate NAD+

Explanation:
Fermentation occurs in the absence of oxygen, and reduces pyruvate to the end product of either ethanol or lactic acid. Since pyruvate is being reduced, NADH is oxidized to NAD+, which is needed for the initial glycolysis reaction to produce pyruvate. During anaerobic respiration, glycolysis is still able to function, but only if NAD+ is available; thus, fermentation allows the regeneration of NAD+ in order for glycolysis to proceed in the absence of oxygen.

Question 45

Which of the following products cannot be directly formed from pyruvate?

Possible Answers:
Acetyl-CoA

None of these can be formed from pyruvate

Ethanol

Lactic acid

Acetaldeyde

Answer 45

Ethanol

Explanation:
Pyruvate can be decarboxylated to make acetyl-CoA. This is the process that initiates the citric acid cycle. Pyruvate can also undergo fermentation, and be reduced to either lactic acid or acetaldehyde. Acetaldehyde can then be reduced to ethanol, however, pyruvate cannot directly be converted to ethanol.

Question 46

Which process can occur under anaerobic conditions?

Possible Answers:
Pyruvate dehydrogenase complex (PDC)

Electron transport chain

Oxidative phosphorylation

Glycolysis

Kreb’s cycle

Answer 46

Glycolysis

Explanation:
Glycolysis occurs in the cytosol and does not require oxygen. The pyruvate dehydrogenase complex (PDC) and Kreb’s cycle require oxygen indirectly, while the electron transport chain and oxydative phosphorylation require oxygen directly. After glycolysis produces pyruvate, either aerobic respiration or anaerobic respiration can proceed depending on the availability of oxygen.

Question 47

How many molecules of ATP would be produced and available for use if four molecules of glucose were used during anaerobic respiration?

Possible Answers:
12

8

20

16

Answer 47

8

Explanation:
Two net molecules of ATP are produced via anaerobic cellular respiration.

Question 48

What is the net ATP production if 4 glucose molecules are oxidized in anaerobic conditions?

Possible Answers:
16

12

4

8

32

Answer 48

8
Explanation:
During anaerobic conditions only glycolysis occurs. Glycolysis alone produces 4 ATP per glucose, but requires an input of 2 ATP per glucose. Thus, 2 ATP per glucose are yielded through glycolysis.

Question 49

The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves. The supply of glycogen is limited, and eventually the body must break down free fatty acids (FFAs) through a process called beta-oxidation.

Which organ in the body cannot perform beta-oxidation, thus requiring the use of ketone bodies when stores of glucose are depleted?

Possible Answers:
Muscle

Heart

Liver

Brain

Answer 49

Brain

Explanation:
The brain is unable to perform beta-oxidation of free fatty acids in the event of a prolonged fasting state. It is important to know this aspect of metabolism. In a fasting state, the liver beta-oxidizes free fatty acids into ketone bodies for the brain to use. Additionally, when energy demands are high, muscles can break down fat for additional ATP.

Unlike other organs in the body, the heart relies almost entirely on beta-oxidation for its energy needs.

Question 50

The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves. The supply of glycogen is limited, and eventually the body must break down free fatty acids (FFAs) through a process called beta-oxidation.

What is the end-product of beta-oxidation?

Possible Answers:
Glucose

Pyruvate

Acetyl-CoA

Acetoacetate

Answer 50

Acetyl-CoA

Explanation:
Free fatty acids are chains of acetyl-CoA molecules linked together. When a free fatty acid undergoes beta-oxidation, it is returned to its component parts of acetyl-CoA. It is important to know that free fatty acids cannot be used to make glucose; they can only be fed into the Krebs cycle.

Question 51

In which of the following places does the breakdown phase of beta-oxidation occur?

Possible Answers:
Mitochondrial intermembrane space

Cytosol

Mitochondrial matrix

Nucleus

Endoplasmic reticulum

Answer 51

Mitochondrial matrix

Explanation:
Beta-oxidation is the metabolization of fatty acids to generate acetyl CoA, which can be used in the Krebs cycle. This process always occurs in the mitochondrial matrix.

Question 52

Which of the following describes a beta oxidation reaction?

Possible Answers:
Acetyl-CoA is converted to fatty acid

Protein is converted to alpha-keto acid

Fatty acid is converted to acetyl-CoA

Glucose is converted to glycogen

Glycogen is converted to glucose

Answer 52

Fatty acid is converted to acetyl-CoA

Explanation:
Beta oxidation is the process by which fatty acid molecules are broken down in the mitochondria to produce acetyl-coA, which can then enter the citric acid (Krebs) cycle. The correct transition from reactant to product for beta oxidation is fatty acid to acetyl-CoA.

Question 53

Fatty acids and cholesterol are stored in tissues as __________ and __________, respectively.

Possible Answers:
triacylglycerols . . . high-density lipoprotein (HDL)

cholesteryl esters . . . ketone bodies

triacylglycerols . . . cholesteryl esters

sphingolipids . . . cholesteryl esters

eicosanoids . . . triacylglycerols

Answer 53

triacylglycerols . . . cholesteryl esters

Explanation:
Fatty acids are stored as triacylglycerols in adipose tissue, while cholesterol is stored as cholesteryl esters in a number of different tissues. Both fatty acids and cholesterol are hydrophobic molecules, which is why they are stored as lipid droplets within their respective tissues.

Question 54

The cellular membrane is a very important structure. The lipid bilayer is both hydrophilic and hydrophobic. The hydrophilic layer faces the extracellular fluid and the cytosol of the cell. The hydrophobic portion of the lipid bilayer stays in between the hydrophobic regions like a sandwich. This bilayer separation allows for communication, protection, and homeostasis.

One of the most utilized signaling transduction pathways is the G protein-coupled receptor pathway. The hydrophobic and hydrophilic properties of the cellular membrane allows for the peptide and other hydrophilic hormones to bind to the receptor on the cellular surface but to not enter the cell. This regulation allows for activation despite the hormone’s short half-life. On the other hand, hydrophobic hormones must have longer half-lives to allow for these ligands to cross the lipid bilayer, travel through the cell’s cytosol and eventually reach the nucleus.

Cholesterol allows the lipid bilayer to maintain its fluidity despite the fluctuation in the body’s temperature due to events such as increasing metabolism. Cholesterol binds to the hydrophobic tails of the lipid bilayer. When the temperature is low, the cholesterol molecules prevent the hydrophobic tails from compacting and solidifying. When the temperature is high, the hydrophobic tails will be excited and will move excessively. This excess movement will bring instability to the bilayer. Cholesterol will prevent excessive movement.

Which of the following hormones utilizes cholesterol as a precursor?

I. Cortisol

II. Aldosterone

III. Mineralocorticoid

Possible Answers:
II only

I, II and III

None of these

III only

I only

Answer 54

I, II and III

Explanation:
Both cortisol and aldosterone are synthesized in the adrenal cortex with cholesterol as the precursor. Mineralocorticoid refers aldosterone, which is also secreted by the adrenal cortex. All of these hormones are steroidal, which means they are derived from cholesterol. Other steroid hormones are the sex hormones.

Question 55

The body attempts to maintain a steady concentration of glucose in the blood, promoting consistent brain function and red blood cell survival. When glucose levels fall, however, the body breaks down glycogen to replenish stores for a short period of time before new glucose molecules are made through the process of gluconeogenesis.

In which organ does gluconeogenesis occur?

Possible Answers:
Liver

Heart

Skeletal muscle

Brain

Answer 55

Liver

Explanation:
Gluconeogenesis, the process of creating new glucose from precursors, occurs in the liver and to a very small extent in the cortex of the kidney. The largest stores of glycogen are also located in the liver, but become quickly depleted in situations of low blood glucose.

Question 56

The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves.

What molecule is broken down by a phosphorylase in the liver to yield glucose-1-phosphate?

Possible Answers:
RNA

Glycosylated protein

Triacylglycerol

Glycogen

Answer 56

Glycogen

Explanation:
Glycogen is the polymer form of glucose, stored in the liver and other tissues when glucose is abundant. When glucose levels are high, glucose-1-phosphate is assembled into branching chains of glycogen. When glucose levels fall, glycogen is broken down by glycogen phosphorylase back into glucose-1-phosphate units. These monomers can be used in glycolysis and cellular respiration. Glycogen is the first source of energy that is used when glucose stores are low.

Question 57

Which of the following cannot be directly converted to acetyl-CoA?

Possible Answers:
Pyruvate

All of these answers can be directly converted to acetyl-CoA

Alpha-keto acid

Glucose

Fatty acids

Answer 57

Glucose

Explanation:
Pyruvate can be converted to acetyl-CoA by decarboxylation. Beta oxidation can convert fatty acids to acetyl-CoA. Transaminases can be used to make alpha-keto acids, which can be converted to acetyl-coA. Glucose cannot be directly converted to acetyl-CoA; it must be transformed into pyruvate first.

Question 58

Which of the following is not an adequate alternative energy source for humans?

Possible Answers:
Glycogen

Cellulose

Alpha-keto acids

Triglycerides

Fatty acids

Answer 58

Cellulose

Explanation:
Carbohydrates can be stored as glycogen in the liver, fats can be stored as triglycerides or fatty acids in adipose tissue, and proteins can be made into alpha-keto acids. Hence, all of these are forms of energy storage that can be used as alternative energy sources.

Cellulose is a polysaccharide that is found in plants. Humans cannot digest cellulose due to its beta-glycosidic linkages.

Question 59

When the body is unable to renew its glucose stores through glycogenolysis and gluconeogenesis, it makes ketone bodies derived from beta-oxidation of free fatty acids. Which of the following is not a ketone body utilized by the brain during periods of starvation?

Possible Answers:
Beta-hydroxybutyrate

Acetone

Aldehyde

Acetoacetate

Answer 59

Aldehyde

Explanation:
The three ketone bodies utilized by the body are acetoacetate, beta-hydroxybutyrate, and acetone. These are produced from acetyl-CoA during beta-oxidation. Acetyl-CoA undergoes conversion reactions to the three ketone bodies in the liver.

Even if you did not know the names of the ketone bodies, you should know that aldehyde is not a ketone because its carbonyl moiety does not have carbons connected from both sides to the carbonyl carbon.

Question 60

Which of these molecules is not a product of the citric acid cycle?

Flavin mononucleotide (FMN)

NADH

Your current choice:
Pyruvate

Ubiquinol (QH2)

CO2

Answer 60

Flavin mononucleotide (FMN)
Flavin mononucleotide (FMN) is not produced by the citric acid cycle. This flavin coenzyme is a reactant, but not a product, since FMN will get reduced to FMNH2.

The rest of the answer choices are products of the citric acid cycle (otherwise known as the Krebs cycle).

Question 61

The citric acid cycle is __________.

both anabolic and catabolic

anabolic

linear

catabolic

Answer 61

both anabolic and catabolic
The citric acid cycle is amphibolic—that is, both anabolic and catabolic. Anabolism occurs when the citric acid cycle generates reduced factors, such as NADH and FADH2. Catabolism occurs when the citric acid cycle oxidizes the two carbon atoms of acetyl CoA to carbon dioxide (CO2).

Question 62

Which enzyme catalyzes the conversion of citrate to isocitrate?

Aconitase

Citrate isomerase

Aldolase

Citrate synthase

Phosphate

Answer 62

Aconitase
Aconitase is the enzyme that catalyzes the conversion of citrate to isocitrate. This essential enzyme is vital in energy production, as it acts like an iron regulatory protein. The conversion of citrate to isocitrate is important since it is needed to react with isocitrate dehydrogenase.