Glycolysis

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Biochemistry › Glycolysis

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1

Glycolysis involves producing energy from carbohydrates. Often times, our foods don't have just glucose, but other sugars such as fructose (in table sugar) and galactose (in milk). Let's consider fructose.

Fructofuranose

Assuming fructose can be phosphorylated by hexokinase, in which step of glycolysis would fructose enter?

Fructose-6-phosphate

Glucose

Fructose-1,6-bisphosphate

glucose-6-phosphate

None of these

Explanation

Fructose can be directly transformed into fructose-6-phosphate by hexokinase.

Phosphofructokinase

2

Glycolysis involves producing energy from carbohydrates. Often times, our foods don't have just glucose, but other sugars such as fructose (in table sugar) and galactose (in milk). Let's consider fructose.

Fructofuranose

Assuming fructose can be phosphorylated by hexokinase, in which step of glycolysis would fructose enter?

Fructose-6-phosphate

Glucose

Fructose-1,6-bisphosphate

glucose-6-phosphate

None of these

Explanation

Fructose can be directly transformed into fructose-6-phosphate by hexokinase.

Phosphofructokinase

3

For each mol of glucose oxidized via cellular respiration, how many total moles of ATP are generated through substrate-level phorphorylation?

Explanation

Cellular respiration is a long process, and so it is easiest to break it into the following steps:

Step 1: Glycolysis

Step 2: Pyruvate decarboxylation

Step 3: Krebs cycle

Step 4: Oxidative phosphorylation

In the above steps, ATP is only produced by substrate-level phosphorylation in glycolysis and during the Krebs cycle.

In glycolysis, two molecules of pyruvate are produced for every molecule of glucose oxidized. During this process, two ATP molecules are consumed, but four are produced via substrate-level phosphorylation.

In the Krebs cycle, each pass of pyruvate through the cycle generates one molecule of GTP, which is subsequently used to generate a molecule of ATP via substrate-level phosphorylation. Thus, one molecule of ATP is produced via substrate-level phosphorylation per molecule of pyruvate oxidized. But remember that glycolysis produces two molecules of pyruvate for each molecule of glucose oxidized. Hence, the Krebs cycle will contribute a total of two molecules of ATP per glucose molecule oxidized.

Since we have a total of four moles ATP from glycolysis and two moles of ATP from the Krebs cycle (one per pyruvate), we have a cumulative production of six moles of ATP generated by substrate-level phosphorylation per mole of glucose oxidized.

4

For each mol of glucose oxidized via cellular respiration, how many total moles of ATP are generated through substrate-level phorphorylation?

Explanation

Cellular respiration is a long process, and so it is easiest to break it into the following steps:

Step 1: Glycolysis

Step 2: Pyruvate decarboxylation

Step 3: Krebs cycle

Step 4: Oxidative phosphorylation

In the above steps, ATP is only produced by substrate-level phosphorylation in glycolysis and during the Krebs cycle.

In glycolysis, two molecules of pyruvate are produced for every molecule of glucose oxidized. During this process, two ATP molecules are consumed, but four are produced via substrate-level phosphorylation.

In the Krebs cycle, each pass of pyruvate through the cycle generates one molecule of GTP, which is subsequently used to generate a molecule of ATP via substrate-level phosphorylation. Thus, one molecule of ATP is produced via substrate-level phosphorylation per molecule of pyruvate oxidized. But remember that glycolysis produces two molecules of pyruvate for each molecule of glucose oxidized. Hence, the Krebs cycle will contribute a total of two molecules of ATP per glucose molecule oxidized.

Since we have a total of four moles ATP from glycolysis and two moles of ATP from the Krebs cycle (one per pyruvate), we have a cumulative production of six moles of ATP generated by substrate-level phosphorylation per mole of glucose oxidized.

5

Which of these is not an end product of glucose metabolism by either aerobic or anaerobic means?

Fructose

Carbon dioxide

Lactate

Ethanol

Explanation

Glucose can be catabolized by both aerobic and anaerobic means. When glucose undergoes oxidative phosphorylation (aerobic metabolism), the end products are carbon dioxide, water, and ATP. In the absence of oxygen, glucose can undergo either lactic acid or alcoholic fermentation. Lactate is a result of lactic acid fermentation, and ethanol and carbon dioxide are results of alcoholic fermentation.

6

Which of these is not an end product of glucose metabolism by either aerobic or anaerobic means?

Fructose

Carbon dioxide

Lactate

Ethanol

Explanation

Glucose can be catabolized by both aerobic and anaerobic means. When glucose undergoes oxidative phosphorylation (aerobic metabolism), the end products are carbon dioxide, water, and ATP. In the absence of oxygen, glucose can undergo either lactic acid or alcoholic fermentation. Lactate is a result of lactic acid fermentation, and ethanol and carbon dioxide are results of alcoholic fermentation.

7

Which of the following is true of glycolysis?

While 2 net ATP are created in glycolysis, there also is a requirement of 2 ATP initially for glycolysis to take place

is formedfrom NADH

All steps are reversible

Glucose is created

Glycolysis speeds up when ATP is plentiful

Explanation

In glycolysis, glucose is broken down. 2 ATP are required for glycolysis to begin, resulting in a creation of 4 ATP. This is a net of 2 ATP. NADH is created from , not the other way around. While 7 of the 10 steps of glycolysis are reversible, the other 3 are irreversible. Finally, if ATP is plentiful, there is no need for glycolysis to speed up (it will actually likely slow down).

8

Which of the following is true of glycolysis?

While 2 net ATP are created in glycolysis, there also is a requirement of 2 ATP initially for glycolysis to take place

is formedfrom NADH

All steps are reversible

Glucose is created

Glycolysis speeds up when ATP is plentiful

Explanation

In glycolysis, glucose is broken down. 2 ATP are required for glycolysis to begin, resulting in a creation of 4 ATP. This is a net of 2 ATP. NADH is created from , not the other way around. While 7 of the 10 steps of glycolysis are reversible, the other 3 are irreversible. Finally, if ATP is plentiful, there is no need for glycolysis to speed up (it will actually likely slow down).

9

In which of these steps of glycolysis is ATP notproduced nor is it hydrolyzed?

Glyceraldehyde-3-phosphate 1,3-bisphosphoglycerate

Glucose glucose-6-phosphate

Fructose-6-phosphate fructose-1,6-bisphosphate

Phosphoenolpyruvate pyruvate

All of these reactions require ATP be used up or synthesized

Explanation

The reaction turning glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate is shown below

This step of glycolysis does not hydrolyze or generate ATP, even though a phosphate group was added onto the glyceraldehyde-3-phosphate. The energy released when is reduced to , sometimes referred to as the energy of oxidation (of glyceraldehyde-3-phosphate).

10

In which of these steps of glycolysis is ATP notproduced nor is it hydrolyzed?

Glyceraldehyde-3-phosphate 1,3-bisphosphoglycerate

Glucose glucose-6-phosphate

Fructose-6-phosphate fructose-1,6-bisphosphate

Phosphoenolpyruvate pyruvate

All of these reactions require ATP be used up or synthesized

Explanation

The reaction turning glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate is shown below

This step of glycolysis does not hydrolyze or generate ATP, even though a phosphate group was added onto the glyceraldehyde-3-phosphate. The energy released when is reduced to , sometimes referred to as the energy of oxidation (of glyceraldehyde-3-phosphate).

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