Chapter 16: Glycolysis Flashcards by Haley Smith | Brainscape

Q

What is the purpose of phosphorylating glucose in cytosol?

A

to trap glucose in the cell and to destabilize glucose and facilitate the next series of metabolic steps

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Q

Which two 3-carbon molecules are generated by the cleavage of fructose-1,6-bisphosphate?

A

glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

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Q

What reaction is catalyzed by aldolase?

A

reversible cleavage of F-1,6-BP to DHAP and GAP

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Q

What is the function of glyceraldehyde 3-phosphate dehydrogenase?

A

oxidation by NAD+ and the formation of acyl phosphate

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Q

What is substrate-level phosphorylation?

A

ATP synthesis when the phosphate donor is a substrate with high-phosphoryl-transfer potential

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Q

What are the primary metabolic fates of pyruvate?

A

ethanol, lactate, and acetyl CoA

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Q

Fructose can enter glycolysis at two distinct points, depending on the tissue. How is fructose metabolized in adipose tissue?

A

Fructose is converted to fructose 6-phosphate.

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Q

How are the glycolytic enzymes regulated?

A

through transcriptional control, through reversible phosphorylation and through allosteric control

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Q

Which of the following must be regenerated for glycolysis to proceed?

A

NAD+

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Q

What type of organism cannot survive in the presence of oxygen?

A

obligate anaerobes

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Q

Which of the following intermediates is needed for the conversion of galactose into glucose by reacting with galactose 1-phosphate?

A

UDP-glucose

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Q

Define: Hexokinase

A

Phosphorylates glucose

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Q

Define: Phosphoglucose isomerase

A

Converts glucose 6-phosphate into fructose 6-phosphate

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Q

Define: Phosphofructokinase

A

Forms fructose 1,6-bisphosphate

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Q

Define: Aldolase

A

Cleaves fructose 1,6-bisphosphate

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Q

Define: Triose phosphate isomerase

A

Catalyzes the interconversion of three-carbon isomers

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Q

Define: Glyceraldehyde 3-phosphate dehydrogenase

A

Generates the first high- phosphoryl-transfer- potential compound that is not ATP

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Q

Define: Phosphoglycerate kinase

A

Generates the first molecule of ATP

Q

Define: Enolase

A

Generates the second

high-phosphoryl- transfer-potential compound that is not ATP

Q

Define: Pyruvate Kinase

A

Generates the second

molecule of ATP

Q

Lactic acid fermentation and alcoholic fermentation are oxidation-reduction reactions. Identify the ultimate electron donor and electron acceptor.

A

In both cases, the electron donor is glyceraldehyde 3-phosphate. In lactic acid fermentation, the electron acceptor is pyruvate, converting it into lactate. In alcoholic fermentation, acetaldehyde is the electron acceptor, forming ethanol.

Q

Each of the following molecules is processed by glycolysis to lactate. How much ATP is generated from each molecule?

Glucose 6-phosphate

A

3 ATP

Q

Each of the following molecules is processed by glycolysis to lactate. How much ATP is generated from each molecule?

Dihydroxyacetone phosphate

A

2 ATP

Q

Each of the following molecules is processed by glycolysis to lactate. How much ATP is generated from each molecule?

Glyceraldehyde 3-phosphate

A

2 ATP

Q

Each of the following molecules is processed by glycolysis to lactate. How much ATP is generated from each molecule?

Fructose

A

2 ATP

Q

Each of the following molecules is processed by glycolysis to lactate. How much ATP is generated from each molecule?

Sucrose

A

4 ATP

Q

Why is it advantageous for the liver to have both hexokinase and glucokinase to phosphorylate glucose?

A

Glucokinase enables the liver to remove glucose from the blood when hexokinase is saturated, ensuring that glucose is captured for later use.

Q

The interconversion of DHAP and GAP greatly favors the formation of DHAP at equilibrium. Yet the conversion of DHAP by triose phosphate isomerase proceeds readily. Why?

A

The GAP formed is immediately removed by subsequent reactions, resulting in the conversion of DHAP into GAP by the enzyme

Q

The recommended daily allowance for vitamin niacin is 15 mg per day. How would glycolysis be affected by niacin deficiency?

A

The conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate would be impaired. Glycolysis would be less effective.

Q

Why can’t the reactions of the glycolytic pathway simply be run in reverse to synthesize glucose?

A

The free energy for the reverse of glycolysis is +90 kJ mol^-1 (+22 kcal mol^-1), far too endergonic to take place.

Q

What are the principle fates of pyruvate generated in glycolysis?

A

Pyruvate can be metabolized to ethanol in alcoholic fermentation, to lactate in lactic acid fermentation, or be completely oxidized to CO2 and H2O in cellular respiration.

Q

What reactions of glycolysis are irreversible under intracellular conditions?

A

The conversion of glucose into glucose 6-phosphate by hexokinase; the conversion of fructose 6-phosphate into fructose 1,6-bisphosphate by phosphofructokinase; the formation of pyruvate from phosphoenolpyruvate by pyruvate kinase.

Q

Phosphofructokinase converts fructose 6-phosphate to fructose 1,6-bisphosphate, the committed step on the pathway that synthesizes ATP. However, some fructose 6-phosphate is converted into fructose 2,6-biphosphate.

Explain why depleting the substrate of PFK to form fructose 2,6-bisphosphate is not a wasteful use of substrate.

A

Substrates are usually present in much higher concentration than their enzymes. Consequently, converting a small amount of substrate into a potent activator of PFK will lead to a rapid increase in the rate of ATP synthesis.

Q

Glucose 6-phosphate:

A

Inhibits hexokinase

Q

Low ATP/AMP ratio:

A

Stimulates phosphofructokinase

Q

Citrate:

A

Inhibits phosphofructokinase in the liver

Q

Low pH:

A

Inhibits phosphofructokinase

Q

Fructose 2,6-bisphosphate;

A

Stimulates pyruvate kinase

Q

Insulin:

A

Causes the insertion of GLUT4 into cell membranes

Q

Has a high KM for glucose:

A

Glucokinase

Q

Transporter specific to liver and pancreas:

A

GLUT2

Q

High ATP/AMP ratio:

A

Inhibits phosphofructokinase

Q

Sucrose is commonly used to preserve fruits. Why is glucose not suitable for preserving foods?

A

Glucose is reactive because its open-chain form contains an aldehyde group.

In other words, glucose is a reducing sugar.

Q

In the liver, fructose can be converted into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate without passing through the phosphofructokinase-regulated reaction.

Show the reactions that make this conversion possible.

Why might ingesting high levels of fructose have deleterious physiological effects?

A

Fructose +ATP –> fructose 1-phosphate + ADP; Fructokinase

Fructose 1-phosphate –> dihydroxyacetone phosphate + glyceraldehyde; Fructose 1-phosphate aldolase

Glyceraldehyde +ATP –> Glyceraldehyde 3-Phosphate + ADP; Triose kinase

The primary controlling step of glycolysis catalyzed by phosphofructokinase is bypassed by the preceding reactions. Glycolysis will proceed in an unregulated fashion.