MCB 181R Chapter 7 Homework

In what organelle is pyruvate oxidation carried out in a cell?

mitochondion

In eukaryotes, pyruvate oxidation takes place in the:

mitochondrial matrix.

The citric acid cycle takes place in the:

mitochondrial matrix.

Refer to the image. The reaction diagrammed:

occurs twice for each glucose oxidized; shows synthesis of the substrate that enters the citric acid cycle; occurs in the mitochondrial matrix.

The citric acid cycle is a cycle because the starting molecule, _____, is regenerated at the end.

oxaloacetate

The loss of electrons is referred to as:

oxidation

Which stages of cellular respiration use O2 as an input?

oxidative phosphorylation

Most of the ATP produced during cellular respiration is generated through:

oxidative phosphorylation.

The mitochondrial electron transport chain is part of:

oxidative phosphorylation.

A molecule that is _____ loses electrons, and a molecule that is _____ gains electrons.

oxidized; reduced

In cellular respiration, glucose is _____ to CO2 and oxygen is _____ to water.

oxidized; reduced

What is the final electron acceptor in the electron transport chain?

oxygen

A simplified overall equation for respiration is as follows: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy In this reaction, we can say that _____ is reduced and _____ is oxidized.

oxygen; glucose

When you exhale, there is more CO2 than was present in the air that you inhaled. This CO2 comes from reactions in:

pyruvate oxidation and the citric acid cycle.

In pyruvate oxidation, the electron donor is _____ and the electron acceptor is _____.

pyruvate; NAD+

What glycolysis products are transported into the mitochondria? Select all that apply.

pyruvate; NADH

The _____ forms of the electron carriers NAD+/NADH and FAD/FADH2 have high potential energy.

reduced

In the absence of oxygen, fermentation:

regenerates NAD+ from the reduction of pyruvate.

Glucose is stored in plants as _____ and in animals as _____.

starch; glycogen

At the end of glycolysis, the carbon originally found in the starting glucose molecule is now present in:

two pyruvate molecule.

The immediate source of electrons for the electron transport chain is:

NADH and FADH2

Which example represents the reduced forms of the two major electron carriers?

NADH and FADH2

Refer to VS Map: Harnessing Energy—Powering the Cell Tour. Which molecule(s) serve as electron donors for the mitochondrial electron transport chain? Select all that apply.

NADH; FADH2

Very low concentrations of detergent make membranes leaky to small molecules and ions without damaging proteins. In isolated mitochondria exposed to detergent, the molecules of the electron transport chain and of ATP synthase remain intact. Do you expect ATP synthesis to continue in the presence of low concentrations of detergent?

No, because with a leaky membrane, the proton gradient cannot be maintained.

Which statement best summarizes cellular respiration?

The chemical potential energy stored in organic molecules is converted to chemical energy that can be used to do the work of the cell.

Refer to the figure shown. Based on your interpretation of the model shown of phosphofructokinase-1 (PFK-1) activity, which alterations might result in an increase in PFK-1 activity? Select all that apply.

a mutation that increases binding affinity for fructose 6-phosphate; a mutation that decreases binding affinity for ATP; a mutation that increases binding affinity for AMP

Energy released by transferring electrons along the electron transport chain is stored as potential energy in the form of:

a proton gradient.

Which of the following are inputs, but not outputs, of glycolysis?

glucose

When a substance in a reaction is oxidized, it:

loses electrons.

Refer to VS Map: Harnessing Energy—Powering the Cell Tour. In which order does one molecule of glucose undergoing cellular respiration go through processes 1-4? 1. glycolysis 2. oxidative phosphorylation 3. pyruvate oxidation 4. citric acid cycle

1>3>4>2

A single molecule of glucose requires _____ "turn(s)" through the citric acid cycle for its chemical energy to be completely harvested.

2

Refer to Animation: Oxidation-Reduction Reactions. Nicotinamide adenine dinucleotide is an electron carrier in many important cellular reactions. It exists in an oxidized form (NAD+) and a reduced form (NADH). What is the missing component in the reaction: NAD+ + ____ + H+ → NADH?

2e-

The enzyme phosphofructokinase-1 (PFK-1) is thought of as a metabolic "valve" that regulates the rate of glycolysis. Which example correctly identifies its allosteric activators and inhibitors and their actions?

ADP-activator; citrate-inhibitor

During the citric acid cycle:

ATP is synthesized by substrate-level phosphorylation.

The conversion of the potential energy of a proton gradient to a form more useful to the cell is achieved by coupling the movement of protons down their electrochemical gradient with the synthesis of ATP. This coupling is made possible by:

ATP synthase.

Refer to VS Map: Harnessing Energy—Powering the Cell Tour. Why is pyruvate imported from the cytoplasm into the mitochondrial matrix?

Although pyruvate is made in the cytoplasm, the product of its oxidation, acetyl-CoA, is a substrate for the citric acid cycle, which is located in the mitochondrial matrix.

Complete oxidation of glucose to CO2 involves two different mechanisms for synthesizing ATP: oxidative phosphorylation and substrate-level phosphorylation. Which is true of substrate-level phosphorylation?

An enzyme catalyzes the transfer of a phosphate group from an organic molecule to ADP to form ATP.

Each molecule of acetyl-CoA that enters the citric acid cycle carries two of the carbon atoms from the original starting glucose molecule. These carbon atoms will ultimately leave the citric acid cycle as carbon atoms in:

CO2

What is the fully oxidized product that results from the pyruvate oxidation stage of cellular respiration?

CO2

When a single pyruvate is converted to acetyl-CoA during pyruvate oxidation, the other products of the reaction are:

CO2 and NADH.

We consume a variety of carbohydrates that are digested into a variety of different monosaccharides. How do these different sugars enter glycolysis?

Different sugars can be modified to form different intermediates of glycolysis.

ATP is not generated directly in the citric acid cycle. Instead, an intermediate is first generated by substrate-level phosphorylation. The intermediate is:

GTP

What happens when glucose is phosphorylated during phase 1 of glycolysis?

Glucose is destabilized so that it can be broken apart in phase 2.

The emperor penguins of Antarctica live on a diet of fish and crustaceans obtained from the cold Antarctic seawaters. During their annual breeding cycle, however, they migrate across the frozen continent to their breeding grounds 50 miles away from the sea (and 50 miles away from their source of food). For over two months, the male emperor penguins care for and incubate eggs, while the females return to the sea to feed. During this time, a male penguin can lose up to 50% of its biomass (by dry weight). Where does this biomass go?

It is converted to CO2 and H2O and then released.

What happens to pyruvate during fermentation?

It is reduced to ethanol or lactic acid.

Production of NADH by glycolysis requires an input of the oxidized molecule NAD+. Where does this supply of NAD+ come from in the absence of oxygen?

It is regenerated by reducing pyruvate to ethanol or lactic acid.

In order for a pathway to produce its products, it must have sufficient inputs. Which input that results from fermentation makes glycolysis possible in anoxic (no oxygen) conditions?

NAD+

Which example is an electron carrier in its reduced form?

NADH

Which statements are true regarding redox reactions? (Note that in redox reactions, the molecule that "causes" another to gain or lose electrons is referred to as the agent.) Select all that apply.

Oxidizing agents accept electrons; If a molecule accepts electrons, it has been reduced; A molecule that has gained H atoms is said to be reduced; Oxidizing agents may accept H+ ions; Redox reactions may involve the transfer of hydrogen ions (H+).

How would you explain why fermentation yields so much less ATP than the yield from aerobic cellular respiration? Select all that apply.

The end products of fermentation are only partially oxidized, compared to the end product of aerobic cellular respiration (CO2); The end products of fermentation retain much more of the starting free energy than CO2.

In 1937, two German biochemists published a paper proposing these reactions as part of glucose oxidation: citrate →isocitrate →α-ketoglutarate →succinate →fumarate →malate →oxaloacetate. Adding succinate, fumarate, or malate to thin slices of tissue increased oxygen consumption, supporting the hypothesis that these molecules are intermediates in the process. However, they were puzzled by the observation that these intermediates were still present in the reaction mixture at the end of the experiment. They had thought that intermediates would be consumed as they were converted to the next molecule in the pathway. What explains the observation that these intermediates were still present?

The pathway is a cycle, constantly regenerating intermediates as glucose is broken down.

Kangaroo rats live in the deserts of the southwestern United States. Kangaroo rats have many adaptations to minimize water loss. They obtain a small amount of water from seeds that they eat. However, the rest of the water they obtain is from cellular respiration.

This could be true, as water is produced in cellular respiration.

Glycolysis is a series of chemical reactions (endergonic and exergonic) by which the cell can obtain ATP. NAD+ plays a crucial role in the reactions of glycolysis by:

accepting electrons during glycolysis, with the overall result that glucose is partially oxidized to pyruvate.

Glycolysis is:

anaerobic.

Animals breathe in air containing oxygen and breathe out air containing less oxygen. The consumed oxygen is used:

as an electron acceptor in the respiratory electron transport chain.

Cellular respiration is a series of _____ reactions.

catabolic

The majority of the energy captured in the citric acid cycle is in the form of:

electrons donated to NAD+ and FAD.

An organism that carries out cellular respiration in its mitochondria:

could be a cell from a terrestrial (land) plant.

The first phase of glycolysis requires the input of two ATP molecules. It is therefore:

endergonic.

Fermentation occurs only in anaerobic conditions.

false

Fermentation produces nearly twice as much ATP as aerobic respiration, which explains why it is a preferred pathway for bacteria.

false

Pyruvate oxidation produces a large amount of ATP through substrate-level phosphorylation.

false

A research group has discovered an organism with cells that contain a previously undescribed organelle. Researchers perform some tests on the isolated organelle to see if it is involved in any major metabolic reactions. To do this, they incubate these organelles for a period of time and determine changes in the amount of various substances in the suspending solution. The results are shown in the table. Based on this analysis, which metabolic process would you conclude could be taking place in this organelle?

glycolysis

Refer to 3D Animation: Harnessing Energy: Aerobic Respiration and the Citric Acid Cycle. The first stage in the production of ATP via the oxidation of glucose molecules is referred to as:

glycolysis.

Glycolysis results in the partial oxidation of glucose to pyruvate. This means that:

in the process of the conversion of glucose to pyruvate, some potential energy is transferred to NADH and ATP.

Based on your interpretation of this model of phosphofructokinase-1 (PFK-1) activity, which of the following would increase PFK-1 activity?

increased concentration of AMP

Based on your interpretation of this model of phosphofructokinase-1 (PFK-1) activity, which of the following would decrease PFK-1 activity?

increased concentration of citrate

Certain complexes of the mitochondrial electron transport chain pump protons. Protons are pumped across the _____ mitochondrial membrane, from the _____ to the _____.

inner; matrix; intermembrane space

Refer to Animation: Harnessing Energy: Electron Transport Chain. Protons in a mitochondrion flow through an ATP synthase from the:

intermembrane space to the matrix.

On completion of either ethanol or lactic acid fermentation, the yield is only two ATP molecules per glucose molecule. The remaining chemical energy from the glucose is found primarily in:

lactic acid and ethanol.

In glycolysis, ATP is synthesized by:

substrate-level phosphorylation.

During glycolysis, _____ phosphorylation adds phosphate groups to ADP by _____.

substrate-level; enzymatic transfer

The energy in organic molecules is released in a series of steps, rather than a single step, because:

the amount of energy released would be too much to capture in one reaction.

Conditions that reduce the strength of the proton gradient across the inner mitochondrial membrane slow the production of ATP by ATP synthase.

true

Even though the full oxidation of glucose is exergonic, some of the reactions in cellular respiration are endergonic.

true

The majority of organisms on Earth can carry out some form of glycolysis.

true

Although glycolysis produces four molecules of ATP by substrate-level phosphorylation, the net gain of ATP for the cell is two molecules. This is because:

two molecules are used in the initial stage.

Of the 6 carbons in a starting molecule of glucose, at the completion of pyruvate oxidation, _____ carbons are fully oxidized to _____, while _____ carbons remain in _____.

two; CO2; four; acetyl groups