Chapter 16 Glycolysis
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) obligate anaerobes
b) AMP
c) pyruvate
d) NAD+
e) glucose
f) UDP-glucose
g) GLUT5
h) facultative anaerobes
i) ATP
j) magnesium
k) galactokinase
l) GLUT2
m) galactose isomerase
1.
____________ is the principle carbohydrate in living systems.
2.
____________ This is the product of aerobic glycolysis.
Ans: c
Section: Introduction
3.
____________ These organisms cannot survive in the presence of oxygen.
Ans: a
Section: 16.2
4.
____________ This substance must be regenerated for glycolysis to proceed.
Ans: d
5.
____________ This intermediate is necessary for the conversion of galactose to glucose.
Ans: f
Section: 16.3
Ans: e
Section: Introduction
Chapter 16 Glycolysis
2
6.
____________ This molecule is an allosteric inhibitor of phosphofructokinase.
7.
____________ This transporter is responsible for fructose uptake in the intestine.
Ans: g
Section: 16.4
8.
____________ The enzyme responsible for converting galactose to be used in the glycolytic
pathway.
Ans: k
Section: 16.3
9.
____________ is the transporter found in the pancreas and liver.
Ans: l
Section: 16.4
10.
Ans: b
Section: 16.4
____________ This is an allosteric activator of glycolysis.
Fill–in-the-Blank Questions
11.
Glycolysis produces a net of moles of ATP per one mole of glucose.
Ans: 2, two Section: 16.1
12.
Glucose is the most stable hexose because the hydroxyl groups are all in the position.
Ans: equitorial Section: Introduction
13.
The key regulatory enzyme for glycolysis is .
Ans: phosphofructokinase Section: 16.1
14.
are enzymes that catalyze the transfer of a phosphoryl group from ATP to an acceptor.
Ans: Kinases Section:16.1
15.
The regeneration of in the reduction of pyruvate to lactate sustains glycolysis under
anaerobic conditions.
Ans: NAD+ Section: 16.2
16.
In alcoholic fermentation, the decarboxylation of pyruvate requires a coenzyme that contains the
vitamin .
Ans: thiamine or B1 Section: 16.2
Ans: i
Section: 16.4
Chapter 16 Glycolysis
3
17.
A potent allosteric activator of liver phosphofructokinase is , which is produced from
fructose-6-phosphate by PFK2.
18.
In the absence of oxygen, increases the expression of most glycolytic enzymes and the
glucose transporters GLUT1 and GLUT3.
Ans: HIF-1, or hypoxia-inducible transcription factor Section: 16.4
19.
The first irreversible enzymatic reaction unique to a metabolic pathway is called the step.
Ans: committed Section: 16.4
20.
mediate the thermodynamically downhill movement of glucose across plasma membranes.
Ans: Glucose transporters Section: 16.4
Multiple-Choice Questions
21.
Which of the following are reasons that glucose is a common metabolic fuel used by living
organisms?
A)
It has a stable ring structure and is unlikely to glycosylate proteins.
B)
It has been found as one of the monosaccharides formed under prebiotic conditions.
C)
It is the only sugar used by the brain.
D)
A and B.
E)
A, B, and C.
Ans: D Section: Introduction
22.
What is the purpose of phosphorylating glucose in cytosol?
A)
to trap glucose in the cell
B)
to destabilize glucose and facilitate the next series of metabolic steps
C)
to convert it to a more soluble form
D)
All of the above.
E)
A and B.
Ans: E Section: 16.1
23.
What two 3-carbon molecules are generated by the cleavage of fructose-1,6-bisphosphate?
A)
glyceraldehyde-3-phosphate and 3-phosphoglycerate
B)
glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
C)
pyruvate and phosphoenolpyruvate
D)
enolase and 2-phosphoglycerate
E)
glyceraldehyde-3-phosphate and pyruvate
Ans: B Section: 16.1
24.
What is a common mechanistic feature of kinases?
A)
Phosphoryl groups are transferred from AMP to an acceptor.
B)
Binding of substrate induces cleft closing.
C)
It converts aldoses to ketoses.
D)
All of the above.
E)
None of the above.
Ans: fructose-2,6-bisphosphate Section:16.4
Chapter 16 Glycolysis
4
25.
What reaction is catalyzed by aldolase?
A)
isomerization of DHAP to GAP
B)
ligation of GAP and DHAP
C)
reversible cleavage of F-1,6-BP to DHAP and GAP
D)
cleavage of DHAP to GAP
E)
irreversible aldol condensation of DHAP and GAP
26.
What is the function of glyceraldehyde 3-phosphate dehydrogenase?
A)
oxidation by NAD+ and formation of acyl-phosphate
B)
oxidation of the alcohol to an aldehyde
C)
dehydration and dephosphorylation of GAP
D)
hydrolysis of GAP
E)
None of the above.
Ans: A Section: 16.1
27.
What is the function of a thioester intermediate such as the one formed from GAP?
A)
It speeds up the actual reaction so that more product can be made.
B)
The thioester shifts the equilibrium of the first stage of the reaction.
C)
The thioester allows the two-step reaction to be coupled so the second reaction, the
energetically unfavorable phosphorylation, can proceed.
D)
The thioester intermediate induces a conformational change that alters the enzyme
specificity.
E)
The thioester prevents the formation of metabolically unfavorable side products.
Ans: C Section: 16.1
28.
What is substrate-level phosphorylation?
A)
phosphorylation of AMP by ATP
B)
ATP synthesis when the phosphate donor is a substrate with high phosphoryl transfer
potential
C)
phosphorylation of glycolytic intermediates
D)
phosphorylation of ATP coupled to an ion gradient
E)
ATP and AMP synthesis from two molecules of ADP
Ans: B Section: 16.1
29.
What type of enzyme catalyzes the intramolecular shift of a chemical group?
A)
hydrolase
D)
B)
kinase
E)
C)
dehydrogenase
Ans: D Section: 16.1
30.
What are the primary metabolic fates of pyruvate?
A)
ethanol
D)
B)
lactate
E)
C)
acetyl CoA
Ans: D Sections: 16.1 and 16.2
Ans: C Section: 16.1
Chapter 16 Glycolysis
5
31.
Fructose can enter glycolysis at two distinct points, depending on the tissue. How is fructose
metabolized in adipose tissue?
A)
Fructose is cleaved to two molecules of GAP.
B)
Fructose is converted to fructose-1-phosphate.
C)
Fructose is converted to fructose-6-phosphate.
D)
Fructose is cleaved to GAP and DHAP.
E)
Fructose is converted to glucose, which enters the pathway.
32.
Lactose intolerance is caused by a deficiency of:
A) lactase. B) elastase. C) lactose D) sucrase E) None of the above.
Ans: A Section: 16.3
33.
How are the glycolytic enzymes regulated?
A)
transcriptional control
D)
B)
reversible phosphorylation
E)
C)
allosteric control
Ans: D Section: 16.4
34.
Cancer driven hypoxia brings about the induction of which genes involved in glycolysis?
A)
GLUT3
B)
hexokinase
C)
aldolase
D)
All of the above.
E)
None of the above.
Ans: D Section: 16.4
35.
During exercise, glycolysis is stimulated by a:
A)
high-energy charge of the cell.
B)
feed-forward stimulation of pyruvate kinase.
C)
negative feedback inhibition on hexokinase.
D)
A and C.
E)
All of the above.
Ans: B Section: 16.4
36.
The release of insulin from β cells in the pancreas in response to increase of blood glucose
levels follows a multistep process. You want to design a drug to overcome what you think might
be the step that is impaired in diabetes. What might this drug do?
A)
activate K+ channels
B)
block Ca2+ channels
C)
decrease ATP/ADP ratios
D)
inhibit GLUT5 synthesis
E)
stimulate GLUT2 synthesis
Ans: E Section: 16.5
Ans: C Section: 16.3
Chapter 16 Glycolysis
6
37.
What is significant about the fact that glucokinase is found in liver and β cells of the pancreas
and that hexokinase is found in most cells?
A)
At low glucose levels, very little is taken up by the liver, so glucose is pared for other
tissues.
B)
Hexokinase is not inhibited by glucose 6-phosphate, allowing accumulation in muscle for
storage as glycogen.
C)
Glucokinase phosphorylates glucose when blood glucose levels are low.
D)
Hexokinase has a high KM, so it does not become saturated until blood glucose levels are
extremely high.
E)
The role of hexokinase is to provide glucose 6-phosphate for the synthesis of fatty acids.
38.
How and why are pyruvate kinase isozymes regulated differently?
A)
In muscle, phosphorylation of pyruvate kinase diminishes its activity in response to low
blood-glucose levels.
B)
In muscle, dephosphorylation of pyruvate kinase is activated in response to high levels of
fructose 1,6-bisphosphate.
C)
In the liver, phosphorylation of pyruvate kinase diminishes its activity in response to low
blood-glucose levels.
D)
In the liver, dephosphorylation of pyruvate kinase is activated in response to high levels
of fructose 1,6-bisphosphate.
E)
In the liver, activation of the GLUT2 receptors increases ATP synthesis leading to a
decrease in pyruvate kinase activity.
Ans: C Section: 16.4
39.
Fermentation occurs in the absence of oxygen, but O2 is not found in any of the reactions of
glycolysis or fermentation. So, what drives these reactions at the level of glycolysis and
fermentation?
A)
NADH synthesized in glycolysis is used to oxidize pyruvate to acetyl CoA during
fermentation reactions.
B)
ATP is synthesized in glycolysis, only if NAD+ is regenerated during fermentation.
C)
Pyruvate donates electrons to NADH in lactic acid fermentation.
D)
In the formation of ethanol, pyruvate is decarboxylated in a reversible reaction, once
oxygen is present again.
E)
In the formation of ethanol, acetaldehyde accepts electrons from NADH, regenerating
NAD+.
Ans: B Section: 16.2
Short-Answer Questions
40.
Why is it important that the glycolytic and gluconeogenic pathways are reciprocally regulated?
taking place in the cell at the same time, thereby preventing the waste of energy that
would occur if glucose was simultaneously being synthesized and metabolized.
Section: Introduction
Ans: A Section: 16.4
Chapter 16 Glycolysis
7
41.
Why is glucose the most stable hexose?
42.
Both hexokinase and glucokinase phosphorylate glucose. The function of glucokinase is to
phosphorylate glucose in liver cells as a means to regulate blood-sugar levels. Would you expect
its Km to be higher or lower than hexokinase?
at high glucose concentrations, which saturate hexokinase. Hexokinase serves to
phosphorylate glucose (and other hexoses) in the cytosol, and has a higher affinity for
glucose, or a lower Km value.
Section: 16.4
43.
What two isomerization reactions occur in glycolysis? Why are these steps necessary?
ketose, which then allows phosphorylation at the number 1 carbon. Later in the pathway,
dihydroxyacetone-phosphate is converted to glyceraldehyde-3-phosphate, utilizing both
of the molecules formed from fructose-1,6-bisphosphate cleavage.
Section: 16.1
44.
At equilibrium, there is far more DHAP than GAP. Yet the conversion of DHAP by triose
phosphate isomerase proceeds readily. Why?
Ans:
The GAP formed is immediately removed by subsequent reactions, resulting in
conversion of DHAP into GAP by the enzyme.
Section: 16.1
45.
How is the conversion of phosphoenolpyruvate to pyruvate accompanied by ATP formation?
Ans:
The enol phosphate possesses very high potential for phosphoryl transfer, which is due to
the driving force of the tautomerization of the enol to the more stable ketone.
Section: 16.1
46.
Describe the biochemical explanation for galactosemia.
galactosemia.
Section: 16.3
47.
What are fermentations?
Ans:
Fermentations are ATP generating processes in which organic compounds act as both
donors and acceptors of electrons.
Section: 16.2
Ans:
The hydroxyl groups and the hydroxymethyl group are all in the equitorial position,
minimizing steric clashes.
Section: Introduction
Chapter 16 Glycolysis
8
48.
How is glycolysis maintained under anaerobic conditions?
49.
How does citrate influence glycolysis?
need to degrade additional glucose for this purpose.
Section: 16.4
50.
Why is it more sensible for phosphofructokinase to be an important control step, rather than
hexokinase?
G6P is the first step in many different paths. Thus, glycolytic control would not be
maintained by tight regulation of hexokinase.
Section: 16.4
51.
What are glucose transporters and how do the different types of transporters differ?
Section: 16.4
52.
Describe how pyruvate kinase regulation occurs and how this is important in the regulation of
glycolysis.
differentiation between muscle and liver are interesting to avoid liver use of glucose
Section: 16.4
53.
There are several key regulatory steps where glycolysis in muscle is left “on” and in liver the
same pathway is “off” or inhibited. What are these steps and why is this important?
and then at the differences in phosphofructokinase, pyruvate kinase, and their
allosteric/covalent modifiers.
Section: 16.4
Ans:
Pyruvate can be reduced to either lactate or ethanol, and this reaction is accompanied by
the oxidation of NADH to regenerate NAD+.
Section: 16.2
Chapter 16 Glycolysis
9
54.
Describe the two isoforms of pyruvate kinase.
55.
How might a defect in a pancreatic β-cell calcium channel affect insulin release when blood
glucose levels rise?
and release insulin into the blood.
Section: 16.5
Ans:
Two forms exist, called M and L, which predominate in skeletal muscle in liver,
respectively. The two forms differ in their sensitivity to covalent modification.
Section: 16.4