Carbohydrate Metabolism

Question 1

Aerobic glycolysis produces a net yield of ____ ATP

Answer 1

2

Question 2

Acyl phosphates such as 1,3-bisphosphoglycerate have a _____ phosphoryl group transfer potential compared to ATP, which can be recognized by the _____ ΔG°’ values for hydrolysis.
(a) greater; more positive
(b) greater; more negative
(c) lower; more positive
(d) lower; more negative
(e) none of the above

Answer 2

b

Question 3

What are the correct coenzyme forms that correspond to X and Y in the following reaction as catalysed by lactate dehydrogenase (EC 1.1.1.27)?
Pyruvate + X -> Lactate + Y
(a) X = NADH Y = NAD+
(b) X = FMN Y = FMNH2
(c) X = NAD+ Y = NADH
(d) X = FAD Y = FADH2
(e) X = NADH Y = NADP+

Answer 3

a

Question 4

Question 4
https://canvas.qut.edu.au/courses/15061/pages/week-3-carbohydrate-metabolism?module_item_id=1439937

Answer 4

a

Question 5

The importance of the glycolysis pathway, particularly in muscle, is that
(a) cells can produce energy anaerobically
(b) cells can oxidise glucose as a nutrient
(c) cells can convert other nutrients to glucose
(d) cells can produce energy aerobically
(e) cells can produce more energy when exercising

Answer 5

a

Question 6

Phosphofructokinase is allosterically _____ by high concentrations of _____
I. activated; ATP
II. inhibited; ATP
III. inhibited; fructose-2,6-bisphosphate
IV. activated; fructose -2,6-bisphosphate

(a) I, III
(b) II, III
(c) II, IV
(d) I, IV
(e) none of the above

Answer 6

c

Question 7

Glycolytic production of ATP occurs via?

Answer 7

substrate-level phosphorylation

Question 8

Which of the options below is the net equation for aerobic glycolysis?

(a) Glucose + 2 ATP -> 2 lactate + 2 ADP + 2 Pi
(b) Glucose + 2 ADP + 2 Pi + 2 NAD+ -> 2 pyruvate + 2 ATP + 2 NADH + 2 H2O + 4 H+
(c) Glucose + 2 ADP + 2 Pi -> 2 lactate + 4 ATP + 4 H+
(d) Glucose + 2 ATP + 2 NAD+ -> 2 pyruvate + 4 ATP + 4 NADH + 4 H+
(e) Glucose + 2 ADP + 2 Pi + 2 NAD+ -> 2 lactate + 4 ATP + 2 NADH + 4 H+

Answer 8

b

Question 9

Which of the following metabolic conversions is considered to be the major control point of glycolysis?
(a) fructose-1,6-bisphosphate -> dihydroxyacetone phosphate + glyceraldehyde-3-phosphate
(b) glucose -> glucose-6-phosphate
(c) 2-phosphoglyerate -> phosphoenolpyruvate
(d) fructose-6-phosphate -> fructose-1,6-bisphosphate
(e) phosphoenolpyruvate -> pyruvate

Answer 9

d

Question 10

Pyruvate kinase transfers a phosphate group from phosphoenolpyruvate to ADP, forming pyruvate and ATP. The reaction catalysed by this enzyme is essentially irreversible. Which of the following is the best explanation for the irreversible nature of this reaction?

(a) The binding of pyruvate to the active site is relatively weak relative to the binding of phosphoenolpyruvate.
(b) The reaction is coupled to the pyruvate dehydrogenase reaction.
(c) The hydrolysis of ATP is highly favourable.
(d) The change in free energy (ΔG°’) for the overall reaction is large and negative.
(e) There is a different enzyme in the cell which synthesises phosphoenolpyruvate.

Answer 10

d

Question 11

The enzymes responsible for the reaction of the glycolysis pathway are located in?

Answer 11

the cytosol

Question 12

Which of the following is true regarding glycolysis?

I. There is a net oxidation of substrate carbon atoms.
II. There is no net release of free energy.
III. Pyruvate is generated only during aerobic glycolysis.
IV. There is 2 ATP formed for every 2 glucose molecules.

(a) I only
(b) I, IV
(c) I, III, IV
(d) IV only
(e) II, IV

Answer 12

a

Question 13

Which of the following lists shows the enzymes responsible for using ATP in the first stage of glycolysis
(a) hexokinase, glucokinase, phosphofructokinase-1
(b) phosphoglycerate kinase, pyruvate kinase
(c) phosphofructokinase-2, pyruvate kinase
(d) glyceraldehyde phosphate dehydrogenase, enolase
(e) triose phosphate isomerase, phosphoglucomutase

Answer 13

a

Question 14

Which of the following lists shows the enzymes responsible for producing ATP in the second stage of glycolysis
(a) hexokinase, glucokinase, phosphofructokinase-1
(b) phosphoglycerate kinase, pyruvate kinase
(c) phosphofructokinase-2, pyruvate kinase
(d) glyceraldehyde phosphate dehydrogenase, enolase
(e) triose phosphate isomerase, phosphoglucomutase

Answer 14

b

Question 15

The production of ethanol by yeast, and not by human liver, is due to the presence in yeast of which of the following enzymes?
(a) pyruvate kinase
(b) pyruvate decarboxylase
(c) pyruvate dehydrogenase
(d) pyruvate carboxykinase
(e) alcohol oxidase

Answer 15

b

Question 16

The most important regulatory step in the glycolytic pathway is:
(a) the formation of glucose-6-phosphate.
(b) the formation of fructose-6-phosphate.
(c) the formation of fructose 1,6 bisphosphate.
(d) the formation of glyceraldehyde-3-phosphate.
(e) the formation of phosphoenolpyruvate

Answer 16

c

Question 17

The effect of fluoride on glycolysis is to inhibit?

Answer 17

enolase

Question 18

In an anaerobic system that is metabolising glucose as a substrate, which of the following compounds would you expect to increase in concentration following the addition of fluoride?
(a) glucose
(b) phosphoenolpyruvate
(c) glyoxylate
(d) 2-phosphoglycerate
(e) pyruvate

Answer 18

d

Question 19

In glycolysis _____ moles of ATP and _____ moles of NADH are produced per mole of glucose consumed.
(a) 1 ; 1
(b) 2 ; 2
(c) 3 ; 3
(d) 2 ; 1
(e) 1 ; 2

Answer 19

b

Question 20

Allosteric regulation of which of the following enzymes is important in the regulation of glycolysis?
(a) Hexokinase
(b) PFK-1
(c) Pyruvate kinase
(d) Both (a) and (c) are correct.
(e) All of the above are correct.

Answer 20

e

Question 21

Give the biochemical definition of “fermentation” and explain, by describing relevant reactions, how it differs from glycolysis.
Your explanation should include a discussion of the role of NADH in the reaction(s)

Answer 21

In biochemistry, fermentation is defined as metabolic processes that extract energy from carbohydrates in the absence of oxygen. Fermentation normally occurs in an anaerobic
environment.

When no O 2 is available (anaerobic respiration) to reoxidise the NADH produced by the glyceraldehyde 3-phosphate dehydrogenase reaction, electrons from NADH must be passed to
one of the products of glycolysis, such as pyruvate or acetaldehyde, forming lactate or ethanol. Hence, the operation of the glycolytic pathway under anaerobic conditions is fermentation.

Under aerobic conditions (in the presence of O 2), pyruvate produced by glycolysis is oxidised to acetyl CoA, which passes into the tricarboxylic acid cycle. NADH produced in the oxidations passes electrons to O 2, and is recycled to NAD+ allowing the continuation of the glycolytic reactions. These processes are used to generate ATP and known as oxidative phosphorylation.

Question 22

Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans and explain the circumstances that favour each

Answer 22

Under aerobic conditions, pyruvate is oxidised to acetyl CoA and passes through the TCA cycle. Under anaerobic conditions, pyruvate is reduced to lactate to recycle NADH to NAD+ , allowing the
continuation of glycolysis.

Question 23

Why is it more logical and metabolically sensible for phosphofructokinase-1 to be the most important control site in the mammalian glycolytic pathway, rather than hexokinase?

Answer 23

The enzyme hexokinase produces glucose 6-phosphate (G6P). G6P is a substrate used in several metabolic pathways. G6P can potentially travel down the pentose phosphate pathway or be converted to glucose-1-phosphate for glycogenesis. Thus, glycolytic control would not be maintained by tight regulation of hexokinase.

In contrast, phosphofructokinase-1 catalyses the first committed step and first irreversible reaction in the glycolytic pathway. At this point, the molecule is committed to entering the glycolytic path

Question 24

There are a variety of fairly common human genetic diseases in which enzymes required for the breakdown of fructose, lactose, or galactose are defective. However, there are very few cases of people having a genetic disease in which one of the enzymes of glycolysis is
severely affected.
Why do you suppose such mutations are seen so rarely?

Answer 24

The glycolytic pathway is so central to all of cellular metabolism that mutations in glycolytic enzymes would be lethal; embryos with such mutations would not survive

Question 25

In the conversion of glucose to pyruvate via glycolysis, all of the following enzymes participate.
Indicate the order in which they function in the pathway by numbering them.

_____ triose phosphate isomerase
_____ hexokinase
_____ phosphoglucose isomerase
_____ glyceraldehyde 3-phosphate dehydrogenase
_____ pyruvate kinase
_____ phosphofructokinase-1

Which of these enzymes represents a major regulation point in glycolysis?

Which catalyses a reaction in which ATP is produced?

Which catalyses a reaction in which NADH is produced?

Answer 25

4, 1, 6, 2, 5, 7, 3

phosphofructokinase-1

pyruvate kinase

glyceraldehyde 3-phosphate dehydrogenase