Chapter 12

Intermediate in the second half of the pathway

1,3-bisphosphoglycerate, 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate

Phosphate transfer

1,3-bisphosphoglycerate→3-phosphoglycerate phosphoenolpyruvate→pyruvate Substrate-level phosphorylation results in the formation of adenosine triphosphate (ATP) by the direct transfer and donation of a phosphate group to adenosine diphosphate (ADP) from a phosphorylated reactive intermediate. Substrate-level phosphorylation serves as a fast source of ATP and unlike oxidative phosphorylation it is independent of external electron acceptors and respiration in human erythrocytes, which have no mitochondria. In the muscles during oxygen depression, substrate-level phosphorylation can supply the cells with energy. Fate of pyruvate Pyruvate produced in glycolysis can be utilized by cells depending on the needs of the cell at the time. Under aerobic conditions where oxygen levels are high, pyruvate is converted to acetyl-coenzyme A and NADH, which is then oxidized in the citric acid cycle to produce energy most efficiently. The NADH must be oxidized back to NAD+ for glycolysis to continue. However, pyruvate is converted to lactate and NAD+ when oxygen levels in the body are low, which provides NAD+ for glycolysis. Alcoholic fermentation in yeast converts pyruvate to ethanol and carbon dioxide under anaerobic conditions.

What is the metabolic significance of the following observations? Only the liver form of pyruvate kinase is inhibited by alanine.

1. The liver is the mostThe liver is the most active gluconeogenic tissue. Since alanine is an important gluconeogenic precursor, its accumulation in liver is a signal that gluconeogenesis should be activated. active gluconeogenic tissue. Since alanine is an important gluconeogenic precursorThe liver is the most active gluconeogenic tissue. Since alanine is an important gluconeogenic precursor, its accumulation in liver is a signal that gluconeogenesis should be activated., its accumulation in liver is a signal that gluconeogenesis should be activatedThe liver is the most active gluconeogenic tissue. Since alanine is an important gluconeogenic precursor, its accumulation in liver is a signal that gluconeogenesis should be activated.. 2. In addition, alanine accumulatesIn addition, alanine accumulates in muscle under conditions of high metabolic demand, where glycolysis must still function to provide A T P . in muscle under conditions of high metabolic demand, where glycolysis must still function to provide ATPIn addition, alanine accumulates in muscle under conditions of high metabolic demand, where glycolysis must still function to provide A T P ..

How many NADH are produced by glycolysis? 4 2 5 3 1

2

Tconversion of 2 moles of oxaloacetate to glucose. 2oxaloacetate+2ATP+2GTP+2NADH+2H++4H2O→glucose+2CO2+2NAD++2ADP+2GDP+4Pi 2oxaloacetate+2NAD++2H2O→glucose+2CO2+2NADH+2H+ 2oxaloacetate+2NADH+2H++2H2O→glucose+2CO2+2NAD+ 2oxaloacetate+2ATP+2GTP+2NAD++4H2O→glucose+2CO2+2NADH+2H++2ADP+2GDP+4Pi

2oxaloacetate+2ATP+2GTP+2NADH+2H++4H2O→glucose+2CO2+2NAD++2ADP+2GDP+4Pi

In glycolysis, what starts the process of glucose oxidation? hexokinase NADPH ADP FADH2 ATP

ATP

Second half of the pathway that produces energy

ATP is synthesized. Three-carbon compounds start the pathway. Overall reaction: dihydroxyacetone phosphate + glyceraldehyde-3-phosphate\rightarrowpyruvateOverall reaction: dihydroxyacetone phosphate + glyceraldehyde-3-phosphate→pyruvate N A D H + H + is produced.NADH+H+ is produced.

First half of the pathway that requires energy

ATP is utilized. Six-carbon compounds start the pathway. Overall reaction: glucose\rightarrowdihydroxyacetone phosphate + glyceraldehyde-3-phosphateOverall reaction: glucose→dihydroxyacetone phosphate + glyceraldehyde-3-phosphate

Why does it make good metabolic sense for phosphoenolpyruvate carboxykinase, rather than pyruvate carboxylase, to be the primary target for the regulation of gluconeogenesis at the level of control of enzyme synthesis? Because in different conditions pyruvate carboxylase can either catalyzes the first reaction committed to gluconeogenesis or inhibit the process, whereas PEPCK catalyzes the first reaction at any conditions. Because the concentration of pyruvate carboxylase is low. If it is a the primary target for the regulation of gluconeogenesis the lack of pyruvate carboxylase would cause CO2 deactivation which affects the photosynthesis. Because the process of regulation of gluconeogenesis at the level of control of enzyme synthesis by pyruvate carboxylase has much higher energy barrier for activation than in case of PEPCK. Because pyruvate carboxylase has two metabolic roles: replenishment of citric acid cycle intermediates and initiation of gluconeogenesis. PEPCK catalyzes the first reaction committed to gluconeogenesis.

Because pyruvate carboxylase has two metabolic roles: replenishment of citric acid cycle intermediates and initiation of gluconeogenesis. PEPCK catalyzes the first reaction committed to gluconeogenesis.

For yeast fermenting glucose to ethanol, which form or forms of labeled glucose would give the most radioactivity in CO2 and the least in ethanol? C−1 C−2 C−3 C−4 C−5 C−6

C−3 C−4

Methanol is highly toxic, not because of its own biological activity but because it is converted metabolically to formaldehyde, through action of alcohol dehydrogenase. Part of the medical treatment for methanol poisoning involves administration of large doses of ethanol.

Ethanol will generate NADH, Ethanol will generate N A D H , through the action of alcohol dehydrogenase, and this will reduce formaldehyde back to methanol, also through alcohol dehydrogenase. The acetaldehyde formed can be metabolized further to acetate. Ethanol may also compete with methanol for binding to alcohol dehydrogenase.

Which of these is NOT a product of glycolysis? pyruvate FADH2 ATP NADH

FADH2

How many high-energy phosphates are generated or consumed in converting 1 mole of glucose to lactate and 2 moles of lactate to glucose

In converting 1 mole of glucose to lactate a total of 2 ATP equivalents are generated.

Complete the sentence to indicate whether ATP equivalents are generated or consumed in converting 2 mole of lactate to glucose, and the total number.

In converting 2 moles of lactate to glucose a total of 6 ATP equivalents are consumed.

reactions of glycolysis

Isomerization: The process where the reactant and the product differ in structure while their molecular formulas remain the same is called isomerization. Phosphorylation: The process of adding a phosphate group, often indicated by the prefix phospho or the word phosphate, is called phosphorylation. Phosphate transfer: The process of transfer of a phosphate group, often indicated by the prefix phospho or the word phosphate, from reactant to ADP to form ATP is called phosphate transfer.

Which of the following are products of glycolysis? 1) ATP 2) pyruvate 3) NAD+ 4) NADP+ Only 2 and 4 are products of glycolysis. Only 1 and 3 are products of glycolysis. Only 1, 2, and 3 are products of glycolysis. Only 1 and 2 are products of glycolysis.

Only 1 and 2 are products of glycolysis.

In liver, glucagon stimulates glycogen breakdown via cAMP. Although you might expect glucagon to stimulate catabolism of the glucose formed as well, glucagon inhibits glycolysis and stimulates gluconeogenesis in liver. The function of glucagon is to increase blood glucose pressure. All the mentioned processes are consistent with this function. The function of glucagon is to decrease blood glucose concentration. All the mentioned processes are consistent with this function. The function of glucagon is to increase blood glucose concentration. All the mentioned processes are consistent with this function. The function of glucagon is to decrease blood glucose pressure. All the mentioned processes are consistent with this function.

The function of glucagon is to increase blood glucose concentration. All the mentioned processes are consistent with this function.

An individual with a glucose-6-phosphatase deficiency suffers from chronic hypoglycemia. The glucose-6-phosphatase deficiency would interfere with release of glucose from the liver for export to other tissues. The glucose-6-phosphatase deficiency would allow all of the glucose to participate in citric acid cycle. The glucose-6-phosphatase deficiency would interfere with production of ATP, and so there would be lack of glucose. The glucose-6-phosphatase is the catalyst for glucose manufacturing reactions.

The glucose-6-phosphatase deficiency would interfere with release of glucose from the liver for export to other tissues.

Hexokinase IV has a Km value that is substantially higher than the Km for other hexokinases. What is the significance of this fact? The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are low. The higher Km reflects high affinity for its substrate, and therefore this kinase is only operational when glucose levels are high. The higher Km reflects higher affinity for its substrate, and therefore this kinase is only operational when glucose levels are low. The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are high.

The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are high.

Anaerobic glycolysis can produce ATP at a much faster rate than aerobic oxidative phosphorylation. True False

True

Calculate the ATP yield per mole of sucrose metabolized by anaerobic glycolysis starting with hydrolytic cleavage.

Yield = 4 mol

Calculate the ATP yield per mole of sucrose metabolized by anaerobic glycolysis starting with phosphorolytic cleavage.

Yield = 5 mol

Intermediate in the first half of the pathway

fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate, dihydroxyacetone phosphate, glucose-6-phosphate, fructose-6-phosphate

The reaction catalyzed by PFK−2. fructose−6−phosphate+ATP→fructose−2,6−bisphosphate+ADP α−D−glucose+Mg2+⋅ADP→α−D−glucose−6−phosphate+ATP+H+ fructose−6−phosphate+ADP→fructose−2,6−bisphosphate+ATP α−D−glucose+Mg2+⋅ATP→α−D−glucose−6−phosphate+ADP+H+

fructose−6−phosphate+ATP→fructose−2,6−bisphosphate+ADP

The conversion of glucose to UDP−Glc. glucose+ATP+UDP→UDP−Glc+Pi+ADP glucose+ATP+UTP→UDP−Glc+PPi+ADP glucose+ADP+Pi+UDP→UDP−Glc+ATP glucose+ADP+UTP→UDP−Glc+ATP

glucose+ATP+UTP→UDP−Glc+PPi+ADP

Isomerization

glucose-6-phosphate→fructose-6-phosphate dihydroxyacetone phosphate→glyceraldehyde-3-phosphate

Phosphorylation

glucose→glucose-6-phosphate fructose-6-phosphate→fructose-1,6-bisphosphate

14CO2 was bubbled through a suspension of liver cells that was undergoing gluconeogenesis from lactate to glucose. Which carbons in the glucose molecule would become radioactive? Check all that apply. C−1 C−2 C−3 C−4 C−5 C−6 none

none

What enzyme catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate? phosphofructokinae fructose-1,6-bisphosphate aldolase glucose-6-phosphate isomerase The reaction is spontaneous and does not require an enzyme to catalyze the reaction.

phosphofructokinase

Which of the following enzymes is NOT part of gluconeogenesis? phosphofructokinase fructose-1,6-bisphosphatase phosphoenolpyruvate carboxykinase pyruvate carboxylase

phosphofructokinase

In glycolysis, ATP molecules are produced by _____. photophosphorylation oxidative phosphorylation substrate-level phosphorylation cellular respiration photosynthesis

substrate-level phosphorylation

Glycolysis is regulated primarily by: phosphorylation of phosphofructokinase. allosteric effectors of pyruvate kinase. three strongly exergonic, nonequilibrium reactions. the availability of glucose-6-phosphate. three strongly endergonic, nonequilibrium reactions.

three strongly exergonic, nonequilibrium reactions.