Biochemistry : Glycolysis

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Reactants And Products Of Glycolysis

How many pyruvates are created from the complete glycolysis of one molecule of glucose?

Possible Answers:

Correct answer:

Explanation:

Glucose is a six-carbon molecule, and pyruvate is a three carbon molecule. From the name, we know that glycolysis involves the lysis, or splitting of glucose. As such, the products of glycolysis include two molecules of pyruvate.

Example Question #1 : Reactants And Products Of Glycolysis

Which of the following is true about the glycolysis pathway?

Possible Answers:

Each pyruvate contains two carbon atoms.

There is a net gain of two ATP molecules for each glucose broken down.

Each glucose molecule is converted into three molecules of pyruvate.

One NADH molecule is formed per molecule of glucose.

 gas is required for glycolysis to occur.

Correct answer:

There is a net gain of two ATP molecules for each glucose broken down.

Explanation:

Each glucose molecule is converted into two pyruvate molecules, with three carbon atoms each. During glycolysis, two NADH molecules are formed per glucose. Oxygen is not necessary -- one major feature of glycolysis is that it produces energy anaerobically. It yields ATP, with a net gain of two ATP molecules for each glucose consumed.

Example Question #1 : Reactants And Products Of Glycolysis

What is the net yield of ATP from glycolysis?

Possible Answers:

Correct answer:

Explanation:

Two separate steps of glycolysis each create 2 ATP (4 ATP total). However, the first and third steps involved in this process require an input of energy in order to work. Thus, the net yield of ATP from glycolysis is actually only 2 ATP. These ATP are produced via substrate-level phosphorylation.

Example Question #41 : Glycolysis

Which process involved in cellular respiration does not yield any high energy phosphate bonds?

Possible Answers:

Pyruvate dehydrogenase complex

All of these produce new high energy phosphate bonds

Krebs cycle

Electron transport chain/ATP synthase

Glycolysis

Correct answer:

Pyruvate dehydrogenase complex

Explanation:

Glycolysis has a net yield of 2 ATP per glucose molecules. The Krebs cycle produces 2 GTP molecules per glucose. The electron transport chain and ATP synthase are the main producers of ATP in cellular respiration. The pyruvate dehydrogenase complex, however, does not yield any ATP (or any other nucleoside phosphates). It simply produces acetyl-CoA from pyruvate, releasing one molecule of carbon dioxide per pyruvate.

Example Question #42 : Glycolysis

What enzymes in the glycolysis pathway in the liver catalyze irreversible reactions?

Possible Answers:

Glucokinase, pyruvate kinase, enolase

Aldolase, phosphofructokinase-1, mutase

Isomerase, aldolase, mutase

Glucokinase, phosphoglycerate kinase, mutase

Glucokinase, phosphofructokinase-1, pyruvate kinase

Correct answer:

Glucokinase, phosphofructokinase-1, pyruvate kinase

Explanation:

In the liver, glucokinase irreversibly converts glucose in the cell to glucose-6-phosphate. Phosphofructose kinase-1 irreversibly converts fructose-6-phosphate to fructose-1,6-bisphosphate. Pyruvate kinase converts phosphoenolpyruvate to pyruvate. All the other enzymes listed catalyze reversible glycolysis reactions.

Example Question #51 : Carbohydrate Metabolism

Which of the following is not a possible fate of the glucose which is taken into cells?

Possible Answers:

Oxidation to pyruvate via glycolysis

Storage as glycogen

Oxidation to ribose-5-phosphate via pentose phosphate pathway

Oxidation to pyruvate via gluconeogenesis

Synthesis into the extracellular matrix structure

Correct answer:

Oxidation to pyruvate via gluconeogenesis

Explanation:

Gluconeogenesis does not convert glucose into pyruvate, rather it builds glucose from non-carbohydrate organic compounds. All of the other answer choices are possible fates of glucose once it enters the cell.

Example Question #2 : Other Glycolysis Concepts

How many steps are required to complete glycolysis?

Possible Answers:

Nine

Eight

Four

Ten

Correct answer:

Ten

Explanation:

Glycolysis is a process that takes place via ten reactions, involving the activity of multiple enzymes and occurs in the cytoplasm of the cell in two distinct phases: an energy consumption phase and an energy production phase. The first step in glycolysis is the conversion of glucose to glucose-6-phosphate through the consumption on one ATP molecule. Glucose is reacted upon by the enzyme hexokinase to carry out this step. Kinases are a group of enzymes that add phosphate groups by removing them from an ATP. In the second step, glucose-6-phosphate is then reacted upon by phosphoglucose isomerase. Isomerases are a group of enzymes that rearranged the structure of a molecule without changing the molecular formula. In this case the phosphoglucose isomerase rearranges the glucose-6-phosphate into fructose-6-phosphate. The third step involves another kinase: phosphofructokinase-1. This enzyme attached another phosphate group to fructose-6-phosphate, creating fructose-1,6-bisphosphate. In the fourth step, this molecule is then reacted upon by fructose bisphosphate aldolase. An aldolase is an enzyme that creates or breaks carbon-carbon bonds. This step results in the creation of two molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. The fifth step involves another isomerase, triose phosphate isomerase, which converts the dihydroxyacetone into glyceraldehyde-3-phosphate (G3P).The sixth step involves the enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). GAPDH moves a hydrogen onto the electron acceptor . A phosphate group from inorganic phosphate instead of ATP replaces the hydride group that was taken from G3P. This creates the molecule 1,3 bisphosphoglycerate. The seventh reaction involves yet another kinase, phosphoglycerate kinase. Kinases can also take phosphate groups away. During this step, two phosphate groups are transferred from the 1,3 Bisphosphoglycerate molecules onto 2 molecules of ADP to create two molecule of ATP. The 1,3 Bisphosphoglycerate then becomes 3-phosphoglycerate. The eighth reaction involves the enzyme phosphoglycerate mutase which is essentially another isomerase. It converts 3-phosphoglycerate to 2-phosphoglycerate. The ninth reaction involves the enzyme enolase which produces a double bond by removing the hydroxyl group on 2-phosphoglycerate which results in phosphoenolpyruvate (PEP). The tenth and final reaction of glycolysis involves the enzyme pyruvate kinase. Just like the previous kinase reaction, this kinase is going to remove phosphate groups from the molecule to produce 2 molecules of ATP (one per molecule of PEP created from 1 molecule of glucose. The final product of glycolysis is pyruvate.

Example Question #2 : Other Glycolysis Concepts

Which of the following is correct regarding glycolysis?

Possible Answers:

Fructose-2,6-bisphosphate is an inhibitor of phosphofructokinase

Glucose is converted to lactose

Hexokinase is found in the liver

The "committed" reaction is also the rate-limiting reaction

Correct answer:

The "committed" reaction is also the rate-limiting reaction

Explanation:

Phosphofructokinase catalyzes the most regulated step of glycolysis and limits the reaction rate of glycolysis. Glucose is converted to pyruvate during glycolysis, not lactate, which is the case in some organisms (humans) through the process of fermentation. Glucokinase, not hexokinase is found in the liver, fructose-2,6-bisphosphate activates, not inhibits phosphofructokinase.

Example Question #41 : Glycolysis

How is fructose metabolism handled in the liver?

Possible Answers:

The liver does not have enzymes to metabolize five-carbon carbohydrates

It is phosphorylated by hexokinase to fructose-6-phosphate, which can enter the glycolytic pathway.

An epimerase adds a carbon to fructose and induces a carbon skeleton rearrangement to form glucose, which can undergo glycolysis normally.

It is phosphorylated by fructokinase to fructose-1-phosphate, which is then converted into precursors of glycolytic intermediates. 

Correct answer:

It is phosphorylated by fructokinase to fructose-1-phosphate, which is then converted into precursors of glycolytic intermediates. 

Explanation:

An epimerase inverts the stereochemistry at a particular carbon, but it cannot add additional carbons. While hexokinase can phosphorylate fructose into a glycolytic intermediate in most tissue, the liver does not contain any hexokinase. In the liver, fructose is phosphorylated by fructokinase into fructose-1-phosphate. This is cleaved by an aldolase to form dihydroxyacetone phosphate (DHAP), a glycolytic intermediate, and glyceraldehyde, a precursor to glyceraldehyde-3-phosphate (G3P), another glycolytic intermediate. Glyceraldehyde can either be phosphorylated into G3P or be used to promote fat storage. 

Example Question #4 : Other Glycolysis Concepts

At the end of anaerobic glycolysis, what products are created?

Possible Answers:

Acetyl-CoA

1 Lactate and 1 pyruvate

1 Pyruvate 

2 Pyruvate, 2 NADH, and 2 ATP

2 Lactate and 2 ATP

Correct answer:

2 Pyruvate, 2 NADH, and 2 ATP

Explanation:

This is a slightly misleading question. Glycolysis is an anaerobic process. Its products are always 2 pyruvate, 2 NADH, and 2 ATP. The fate of the pyruvate depends on the absence and/or presence of oxygen, in which it will be reduced into lactate or cleaved into acetyl-CoA to enter the Krebs cycle, respectively.

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