Skip to main content
United States
Jump To
Support
Register or Log In
Support
Register or Log In
✕
Instructors
Browse Products
Getting Started
Students
Browse Products
Getting Started
Return to Biochemistry: The Molecular Basis of Life, Seventh International Edition Student Resources
Chapter 9 Review Quizzes
Aerobic Metabolism I: The Citric Acid Cycle
Quiz Content
*
not completed
.
The citric acid cycle is occasionally called the Krebs Cycle in honor of its discoverer, Hans Krebs. It is also occasionally called the tricarboxylic acid cycle. Why?
The starting material for the citric acid cycle is a tricarboxylic acid
correct
incorrect
The final product of the citric acid cycle is a tricarboxylic acid
correct
incorrect
The first several reactions of the citric acid cycle produce tricarboxylic acids
correct
incorrect
There are more tricarboxylic acids in the cycle than dicarboxylic acids
correct
incorrect
The citric acid cycle is amphibolic
correct
incorrect
*
not completed
.
Glycols are bifunctional alcohols having hydroxyl groups on adjacent carbons and in structure, looking as though hydroxyl groups had been added to a double bond. Ethylene glycol (1,2-dihydroxyethane) is a common component of automotive antifreeze and results in some accidental and deliberate poisonings. Propylene glycol (1,2-dihydroxypropane) may also be used as antifreeze and is advertized as being "environmentally friendly." Actually, it might be appropriate to say that propylene glycol is friendlier to children and pets, as it is not poisonous if consumed in limited quantities. While we often overlook dicarboxylic acids, several take part in metabolism, occasionally with dangerous results. The danger of toxic ethylene glycol is that it is oxidized in the body to form oxalic acid, the smallest dicarboxylic acid, which chelates calcium ion in tissues, resulting in tetany and death. If propylene glycol were oxidized by the body, both the first and second carbon would be oxidized as completely as possible without breaking the carbon chain. Why would the product of the oxidation be unlikely to be poisonous?
Oxidation of propylene glycol would form citric acid, an innocuous compound which could be detoxified by the TCA cycle
correct
incorrect
Oxidation of propylene glycol would form pyruvic acid, which could be metabolized further by pyruvate dehydrogenase
correct
incorrect
Glycols are never metabolized by humans, as they are not found in the food pyramid
correct
incorrect
Propylene glycol would be unlikely to cause intoxication
correct
incorrect
Propylene glycol would form lactic acid, which could be easily metabolized by glycolysis
correct
incorrect
*
not completed
.
The Krebs cycle provides ample opportunity to practice using the IUPAC enzyme classification system. Which of the following is catalyzed by an oxidoreductase?
Acetyl-CoA + oxaloacetic acid → Coenzyme A + citric acid
correct
incorrect
Citric acid → isocitric acid
correct
incorrect
Isocitric acid → carbon dioxide + á-ketoglutaric acid
correct
incorrect
Succinyl CoA + GDP + Pi → GTP + Coenzyme A + succinic acid
correct
incorrect
Fumaric acid + water → malic acid
correct
incorrect
*
not completed
.
Facultative anaerobes have metabolic processes which allow them to:
Generate energy by growing in the presence of oxygen
correct
incorrect
Use oxygen as an electron acceptor, but also protect themselves against molecular oxygen
correct
incorrect
Protect themselves against atmosphere oxygen, but also carry out fermentation
correct
incorrect
Have an absolute requirement for molecular oxygen
correct
incorrect
Use only hydrogen peroxide as an electron acceptor
correct
incorrect
*
not completed
.
What are the first organisms on earth thought to have lived upon?
Groceries from mom and pop stores
correct
incorrect
Ammonia
correct
incorrect
Oxygen
correct
incorrect
Organic molecules produced by natural activities such as lightning, thermal forces, and solar radiation
correct
incorrect
Organic molecules produced in Chem II laboratories and disposed of improperly
correct
incorrect
*
not completed
.
If we consider a mole of NADH to be equivalent in energy to 2.5 ATP and a mole of FADH
2
to be equivalent in energy to 1.5 ATP, what is the total number of moles of ATP Which could be generated by oxidation of a mole of pyruvic acid via the citric acid cycle?
46
correct
incorrect
30
correct
incorrect
23
correct
incorrect
12.5
correct
incorrect
8
correct
incorrect
*
not completed
.
The reduced coenzymes of the TCA cycle, such as FADH2 and NADH, must pass their electrons into the electron transport chain in order to produce ATP, but one step of the TCA cycle yields a compound with high transfer potential which can provide energy for phosphorylation of ADP at the substrate level. What is this high-energy compound?
Citric acid
correct
incorrect
Isocitric acid
correct
incorrect
Fumaric acid
correct
incorrect
Succinyl CoA
correct
incorrect
Succinic acid
correct
incorrect
*
not completed
.
The theft of a five lb. package of a poisonous compound called "1080" recently caused a panic in the police department of a Council Bluffs, Iowa. 1080 Relies for its toxicity on the presence of fluoroacetic acid. Fluoroacetic acid is metabolized to fluorocitric acid, which blocks the citric acid cycle, resulting in an accumulation of citrate in cells. Ranchers in western states once used meat baited with 1080 to kill coyotes. Environmentalists are concerned that eagles may take the poisoned bait. Farmers growing corn are not as concerned with fluoroacetic acid. Why is fluoroacetic acid toxic to coyotes, but not corn?
Coyotes don't eat corn
correct
incorrect
Eagles only eat dead coyotes
correct
incorrect
Plants possess the glyoxylate cycle and are not dependent upon the citric acid cycle
correct
incorrect
Toothpaste has fluoride, and this balances the fluorine taken in with fluoroacetate, slowing the citric acid cycle until the poison is removed from the body
correct
incorrect
Corn does not consume the poisoned baits
correct
incorrect
*
not completed
.
Enzymes of gluconeogenesis can use some intermediates from the citric acid cycle in the formation of glucose. Why, then, can't we put carbons from fatty acids into the cycle as acetyl- CoA and then take molecules out to make glucose?
The citric acid cycle doesn't turn fast enough
correct
incorrect
We need the ATP too badly to waste it this way; for each ATP formed, one is lost
correct
incorrect
Acetyl-CoA doesn't enter the citric acid cycle
correct
incorrect
Citric acid has six carbons and needs them all
correct
incorrect
For every two carbons entering the cycle as acetyl-CoA, two are lost as carbon dioxide
correct
incorrect
*
not completed
.
You may have learned the the term "amphoteric" used in general chemistry to describe a substance which could function as either an acid or a base. When we describe the TCA cycle as amphibolic, we mean that it:
Is capable of both synthetic and degradative reactions
correct
incorrect
Is capable of every kind of reaction imaginable
correct
incorrect
Amplifies substrates so that large, rolling molecules are produced
correct
incorrect
Can carry out anabolic reactions
correct
incorrect
Can carry out catabolic reactions
correct
incorrect
*
not completed
.
Which of the following substances would slow the citric acid cycle?
Oxaloacetic acid and α-ketoglutaric acid
correct
incorrect
Citric acid and succinyl CoA
correct
incorrect
Malic acid and isocitric acid
correct
incorrect
Fumaric acid and succinic acid
correct
incorrect
Malic acid and fumaric acid
correct
incorrect
*
not completed
.
The first step of the citric acid cycle is usually considered to be formation of citric acid. Prior to that step, however, pyruvate must be converted to acetyl Coenzyme A in a reaction catalyzed by pyruvate dehydrogenase. Among the coenzymes need for pyruvate dehydrogenase is thiamine pyrophosphate, also known as vitamin B1. Lack of this vitamin leads to beri-beri, a debilitating disease often suffered by prisoners of war. Which other enzyme system in the citric acid cycle also has a requirement for thiamine pyrophosphate?
Citrate synthase
correct
incorrect
Citrate isomerase
correct
incorrect
Isocitrate oxidoreductase
correct
incorrect
α-Ketoglutarate oxidoreductase
correct
incorrect
Malate oxidoreductase
correct
incorrect
*
not completed
.
Ordinarily, entrance of the carbons of pyruvic acid into the TCA cycle requires loss of one of the carbons. There is, however, an enzyme which can insert all three of the carbons of pyruvate into the TCA cycle. Its name is:
Citrate synthase
correct
incorrect
α-ketoglutarate dehydrogenase
correct
incorrect
Aconitase
correct
incorrect
Pyruvate carboxylase
correct
incorrect
Pyruvate dehydrogenase
correct
incorrect
*
not completed
.
In addition to the regulators of enzyme activity within the citric acid cycle, two enzymes outside the cycle profoundly affect its activity. Which ones?
Isocitrate dehydrogenase and isocitrate oxidase
correct
incorrect
Lactic acid dehydrogenase and pyruvate kinase
correct
incorrect
Acetaldehyde dehydrogenase and citrate synthase
correct
incorrect
Glucokinase and phosphofructokinase
correct
incorrect
Pyruvate carboxylase and pyruvate dehydrogenase
correct
incorrect
*
not completed
.
Oxaloacetic acid can pass into the mitochondrial matrix if it is first converted into:
Glucose
correct
incorrect
Malic acid
correct
incorrect
Glucose-6-phosphate
correct
incorrect
Acetyl-CoA
correct
incorrect
Succinic acid
correct
incorrect
*
not completed
.
Consider the standard reduction potentials of the following reactions:
The free energy change for a typical electrochemical reaction can be expressed by the equation:
ΔG = -nFE
Given the table above and your understanding of the equation for free energy change, which metal from the list would you predict would react most vigorously if dropped into water?
Potassium
correct
incorrect
Copper
correct
incorrect
Zinc
correct
incorrect
Chromium
correct
incorrect
Hydrogen
correct
incorrect
*
not completed
.
The citric acid cycle is a major source of NADH, but on occasion, an excess of citric acid accumulates. Under those conditions, the carbons from citric acid are most likely to wind up in the body as:
Glucose
correct
incorrect
Maltose
correct
incorrect
DNA
correct
incorrect
RNA
correct
incorrect
Lipid
correct
incorrect
*
not completed
.
Clare Booth Luce, United States ambassador to the Vatican, was once poisoned by exposure to fumes from her wallpaper. The wallpaper in her villa was colored with a beautiful green pigment containing mercury. Apparently, her bedroom was located below the laundry, and vibration from the machines released dust containing mercury. Chief among the problems caused by mercury exposure is the fact that mercury attaches to sulfhydryl groups such as those of lipoic acid. Which step of metabolism would be blocked by mercury?
Pyruvate dehydrogenase
correct
incorrect
Citrate synthase
correct
incorrect
α-Ketoglutarateisomerase
correct
incorrect
Aconitase
correct
incorrect
Isocitrate dehydrogenase
correct
incorrect
*
not completed
.
NADH and NADPH are major coenzymes for oxidoreductases. While nearly equivalent in redox potential, the two coenzymes often function in different metabolic actions. In general:
NADPH is used mostly in glycolysis
correct
incorrect
NADPH functions with enzymes involved in fermentation
correct
incorrect
NADH is often involved in degradation and NADPH in synthesis
correct
incorrect
NADH is a coenzyme for lipases
correct
incorrect
NADPH is a coenzyme used by barbarians for energy when they lack cereals
correct
incorrect
*
not completed
.
Animals oxidize carbohydrate and can use fragments of extra carbohydrate such as acetyl- CoA to form lipids. Animals can oxidize lipids and use the energy for metabolic processes, but are incapable of forming carbohydrate from lipids. Plants can form carbohydrate from lipids and from fragments such as acetyl-CoA by which of the following mechanisms:
The TCA cycle
correct
incorrect
Anaerobic glycolysis
correct
incorrect
The glyoxylate cycle
correct
incorrect
Pyruvate dehydrogenase
correct
incorrect
Aerobic glycolysis
correct
incorrect
*
not completed
.
Early life forms lived in an atmosphere largely devoid of free oxygen molecules. Most present-day life forms use molecular oxygen as:
Raw material for synthesis of DNA
correct
incorrect
Starting materials for synthesis of lipids
correct
incorrect
The initial substances from which starches such as glycogen or amylopectin are formed
correct
incorrect
The final acceptor for electrons removed from carbons during oxidation
correct
incorrect
The final acceptor for electrons removed from hydrogen during digestion
correct
incorrect
*
not completed
.
It is estimated that, in 1916, 10,000 sharecroppers are estimated to have died in the southern United States due to pellagra, a disease characterized by dermatitis, dementia and weakness caused by lack of nicotinamide. Nicotinamide is an essential component of coenzymes:
NADH and NADPH
correct
incorrect
ATP and GTP
correct
incorrect
Citric acid
correct
incorrect
ATP synthase
correct
incorrect
Cell membranes
correct
incorrect
Previous Question
Submit Quiz
Next Question
Reset
Exit Quiz
Review & Submit
Submit Quiz
Are you sure?
You have some unanswered questions. Do you really want to submit?
Back to top
Printed from , all rights reserved. © Oxford University Press, 2025
Select your Country