MCB 181R - ch. 7 homework questions
In eukaryotes, pyruvate oxidation takes place in the:
mitochondrial matrix
The citric acid cycle takes place in the:
mitochondrial matrix
In what organelle is pyruvate oxidation carried out in a cell?
mitochondrion
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
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
Most of the ATP produced during cellular respiration is generated through:
oxidative phosphorylation
The mitochondrial election 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
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
Which stage of cellular respiration occurs following production of pyruvate?
pyruvate oxidation
When you exhale, there is more CO2 than was present in the air that you inhaled. This CO2 comes from reaction in:
pyruvate oxidation and the citric acid cycle
Which stage of cellular respiration produce CO2 as a waste product?
pyruvate oxidation, and the citric acid cycle
In pyruvate oxidation, the electron donor is ________ and the electron acceptor is ________
pyruvate; NAD+
During lactic acid fermentation, pyruvate is:
reduced
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
Which of the following summarizes the net final products of glycolysis?
two molecules of pyruvate, two molecules of ATP, and two molecules of NADH
At the end of glycolysis, the carbon originally found in the starting glucose molecule is now present in:
two pyruvate molecule
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
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
Energy released by transferring electrons along the electron transport chain is stored as potential energy in the form of:
a proton gradient
In the electron transport chain, the energy from high-energy electrons is transformed into _____ before being used to generate ATP.
a proton gradient
Most of the proteins of the electron transport chain are:
embedded in the inner mitochondrial membrane
What is the final electron acceptor in the electron transport chain?
glucose
Which of the following are inputs, but not outputs, of glycolysis?
glucose
What happens when glucose is phosphorylated during phase 1 of glycolysis?
glucose is destabilized so that it can be broken apart in phase 2
When a substance in a reaction is oxidized, it:
loses electrons
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.
- 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 - oxidizing agents accept electrons - redox reactions may involve the transfer of hydrogen ions (H+)
What glycolysis products are transported into the mitochondria? Select all that apply.
- pyruvate - NADH
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
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
How many reactions in glycolysis directly generate ATP by substrate-level phosphorylation?
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-
Tracing the metabolism of one glucose molecule, how many carbon atoms are available for further oxidation at the completion of the pyruvate oxidation stage?
4
Which molecule would you expect to act as allosteric activator of an enzyme in glycolysis?
ADP
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
What is the fully oxidized product that results from the pyruvate oxidation stage of cellular respiration?
CO2
Which of these reactions summarizes the overall reactions of cellular respiration?
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy
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
When a single pyruvate is converted to acetyl-CoA during pyruvate oxidation, the other products of the reaction are:
CO2 and NADH
ATP is not generated directly in the citric acid cycle. Instead, an intermediate is first generated by substrate-level phosphorylation. The intermediate is:
GTP
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+
What product of pyruvate oxidation stage of cellular respiration will have the two electrons that are lost from pyruvate?
NADH
Which example is an electron carrier in its reduced form?
NADH
Which best describes energy captured in ATP during aerobic cellular respiration?
a small amount of energy is captured in ATP by substrate-level phosphorylation; most is captured in ATP by oxidative phosphorylation
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
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
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
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
During glycolysis, pyruvate oxidation, and the citric acid cycle, the chemical energy in glucose is transferred to:
electron carrier and ATP
The majority of the energy captured in the citric acid cycle is in the form of:
electrons donated to NAD+ and FAD
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
In a plant cell, the oxidative phosphorylation stage of cellular respiration is carried out in the cytoplasm.
false
Oxidation is the gain of electrons
false
Pyruvate oxidation produces a large amount of ATP through substrate-level phosphorylation.
false
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
In eukaryotes, fermentation takes place:
in the cytoplasm
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
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
Due to the pumping action of the electron transport chain, protons have a high concentration in the _____ and a low concentration in the _____.
intermembrane space; mitochondrial matrix
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
Pyruvate oxidation is an important stage in cellular respiration because:
it links glycolysis with the citric acid cycle
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
In which stage of aerobic cellular respiration is the most energy transferred from chemical bonds in the fuel molecule to bonds in other molecules?
the citric acid cycle
In eukaryotic cells, glycolysis occurs in:
the cytoplasm
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
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
When glucose is broken down in a cell, all of the energy it stores is not released simultaneously but is instead released in a stepwise process
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 molecule are used in the initial stage
