L15- Glycolysis I

Question 1

What is the net chemical equation for the reactions of anaerobic glycolysis?

Answer 1

Glucose + 2 ADP + 2 Pi -> 2 Lactate + 2ATP + 2 H2O.

Question 2

Which cell type in the human body relies only on glycolysis as a source of ATP?

Answer 2

Erythrocytes (red blood cells) only.

Question 3

What is the major source of ATP in skeletal muscle at rest? During exercise?

Answer 3

Oxidative metabolism at rest; both oxidative phosphorylation and glycolysis during exercise.

Question 4

Which enzyme is most frequently deficient in hemolytic anemias?

Answer 4

Pyruvate kinase.

Question 5

In which cellular compartment does glycolysis occur?

Answer 5

The cytoplasm.

Question 6

Which enzyme(s) converts glucose to glucose-6-phosphate?

Answer 6

Hexokinase and glucokinase.

Question 7

What is the reaction catalyzed by phosphohexose isomerase?

Answer 7

Glucose-6-phosphate -> fructose-6-phosphate.

Question 8

Which glycolytic enzymes catalyze irreversible reactions?

Answer 8

Hexokinase, phosphofructokinase-1(PFK-1) and pyruvate kinase.

Question 9

Which glycolytic enzymes use ATP to phosphorylate their substrate, thereby producing ADP?

Answer 9

Hexokinase and phosphofructokinase-1 (PFK-1).

Question 10

Which glycolytic enzymes catalyze reactions that yield ATP?

Answer 10

Phosphoglycerate kinase and pyruvate kinase.

Question 11

Which glycolytic enzymes catalyze reactions that yield NADH?

Answer 11

Glyceraldehyde-3-phosphate dehydrogenase.

Question 12

Which glycolytic enzymes use inorganic phosphate, and not ATP, to phosphorylate their substrates?

Answer 12

Glyceraldehyde-3-phosphate dehydrogenase (very important!).

Question 13

What is the committed step in glycolysis?

Answer 13

The phosphofructokinase-1 reaction (PFK1).

Question 14

What reaction does phosphofructokinase-2 (PFK-2) catalyze?

Answer 14

Fructose-6-phosphate + ATP -> fructose-2,6-bisphosphate + ADP.

Question 15

In glycolysis, what reaction does the enzyme aldolase catalyze?

Answer 15

Fructose-1,6-bisphosphate -> glyceraldehyde-3-phosphate + dihydroxyacetone-phosphate.

Question 16

The aldolase reaction in glycolysis yields two products. Which one of these products is a direct glycolytic intermediate?

Answer 16

Glyceraldehyde-3-phosphate is the substrate for the next steps of glycolysis. Dihydroxyacetone-phosphate must be isomerized into glyceraldehyde-3-phosphate in order to continue through glycolysis.

Question 17

Which enzyme can be inhibited by the molecule 2-deoxyglucose?

Answer 17

Hexokinase.

Question 18

Which molecules are able to inhibit phosphofructokinase-1 (PFK-1)?

Answer 18

ATP, citrate and fatty acids.

Question 19

Which molecules are able to activate, or relieve inhibition of, phosphofructokinase-1 (PFK-1)?

Answer 19

ADP, AMP, and fructose-2,6-bisphosphate.

Question 20

Which glycolytic enzyme exhibits negative cooperativity?

Answer 20

Glyceraldehyde-3-phosphate dehydrogenase.

Question 21

Which enzyme reversibly isomerizes dihydroxyacetone-phosphate to glyceraldehyde-3-phosphate?

Answer 21

Triose phosphate isomerase.

Question 22

From which vitamin is NAD+ derived?

Answer 22

Vitamin B3 (niacin).

Question 23

How many molecules of NAD+ can the enzyme glyceraldehyde-3-phosphate dehydrogenase bind?

Answer 23

4

Question 24

What is substrate-level phosphorylation?

Answer 24

Substrate-level phosphorylation refers to the formation of ATP (or GTP) by the direct transfer of a phosphate group from a reactive metabolic intermediate to ADP (or GDP).

Question 25

What kind of a reaction is catalyzed by the enzyme enolase?

Answer 25

Dehydration/hydration.

Question 26

The enzyme enolase is strongly inhibited by which molecule?

Answer 26

Fluoride.

Question 27

Which enzyme catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate (PEP)?

Answer 27

Enolase.

Question 28

Which enzyme catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate and ATP?

Answer 28

Pyruvate kinase.

Question 29

How many moles of ATP does pyruvate kinase generate per glucose molecule?

Answer 29

2

Question 30

Which molecules stimulate the activity of pyruvate kinase?

Answer 30

Fructose-1,6-bisphosphate. This phenomenon is called feed-forward stimulation.

Question 31

Which molecules are able to inhibit pyruvate kinase?

Answer 31

Alanine, NADH, ATP, fatty acids, and succinyl-CoA.

Question 32

What is the role of the enzyme lactate dehydrogenase under anaerobic conditions?

Answer 32

Lactate dehydrogenase transfers electrons from NADH to pyruvate, reducing pyruvate to lactate to regenerate NAD+. Regeneration of NAD+ is required if the cell is to continue with glycolysis under anaerobic conditions (remember that NAD+ is a required cofactor for glyceraldehyde-3-phosphate dehydrogenase).

Question 33

Most of the NAD+ in cells is synthesized from niacin (vitamin B3). However, a small amount of NAD+ may be synthesized from which amino acid?

Answer 33

Tryptophan.

Question 34

Niacin deficiency may result in which condition?

Answer 34

Pellagra.

Question 35

List the main symptoms of pellagra.

Answer 35

The symptoms of pellagra are sometimes referred to as ‘the four D’s’: diarrhea, dementia, dermatitis and death.

Question 36

In which cell compartment do the reversible interconversions of lactate, alanine and pyruvate occur?

Answer 36

Cytoplasm.

Question 37

In which cell compartment do the irreversible conversions of pyruvate to oxaloacetate and acetyl-CoA occur?

Answer 37

Mitochondria.

Question 38

Which glycolytic enzymes are allosterically regulated?

Answer 38

Hexokinase, phosphofructokinase-1 (PFK-1) and pyruvate kinase.

Question 39

Which glycolytic enzymes are regulated by phosphorylation?

Answer 39

Pyruvate kinase is inactivated by phosphorylation.

Question 40

The hormone insulin induces the synthesis of which glycolytic enzymes?

Answer 40

Glucokinase and pyruvate kinase.

Question 41

What is the net yield of ATP in the conversion of one glucose molecule to two pyruvates during glycolysis?

Answer 41

Two moles of net ATP are produced per one mole of glucose.

Question 42

Which glycolytic intermediate(s) can be used to synthesize glycogen, polysaccharides, glycoproteins and pentoses?

Answer 42

Glucose-6-phosphate.

Question 43

The pentose phosphate shunt produces NADPH and pentose sugars. Pentose sugars from this shunt may enter the glycolytic pathway as which glycolytic intermediate(s)?

Answer 43

Fructose-6-phosphate and glyceraldehyde-3-phosphate.

Question 44

Which glycolytic product(s) can be reduced to glycerol-3-phosphate, a precursor for fatty acid and phospholipid biosynthesis?

Answer 44

Dihydroxyacetone-phosphate.

Question 45

Which amino acid(s) can be inter-converted with 3-phosphoglycerate?

Answer 45

Serine.

Question 46

Pyruvate can be inter-converted with which amino acid(s)?

Answer 46

Alanine.

Question 47

Which glycolytic intermediate(s) can be oxidized to acetyl-CoA, which is used for synthesis of fatty acids, cholesterol, steroid hormones and oxidative metabolism?

Answer 47

Pyruvate.

Question 48

Which toxic substance is able to inhibit hexokinase?

Answer 48

2-deoxyglucose.

Question 49

Which step of glycolysis is affected by pentavalent arsenic?

Answer 49

Pentavalent arsenic prevents the production of ATP by glyceraldehyde-3-phosphate dehydrogenase. Note, however, that it does not stop the process of glycolysis. It only prevents the net gain of ATP.

Question 50

Which toxic substances can react with the sulfhydryl group of glyceraldehyde-3-phosphate dehydrogenase and block the glycolytic process altogether?

Answer 50

Mercury compounds.

Question 51

How does the regulation of lactate dehydrogenase in skeletal muscle differ from that in cardiac muscle?

Answer 51

In skeletal muscle, when more pyruvate is produced than can enter the TCA cycle, pyruvate will be converted to lactate by lactate dehydrogenase. In the heart, however, rising pyruvate concentrations will inhibit lactate dehydrogenase. This is because lactate is an acid that, in excess, can cause muscle cramps. Therefore, pyruvate inhibition of lactate dehydrogenase in the heart has a protective effect on cardiac function.