Glycolysis and Metabolic Regulation

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Questions and Answers

What is the effect of glucagon on glycolytic enzymes?

Induces key enzymes of glycolysis

Represses key enzymes of glycolysis (correct)

Has no effect on glycolytic enzymes

Increases the activity of glycolytic enzymes

How does fluoride interfere with glycolysis?

By destabilizing glycolytic intermediates

By blocking the activity of enolase (correct)

By inhibiting pyruvate dehydrogenase

By binding to glyceraldehyde-3-P dehydrogenase

Which compound is produced from pyruvate after glycolysis under aerobic conditions?

Lactate

Acetyl Co-A (correct)

Citrate

Acetaldehyde

In which condition does anaerobic respiration primarily occur?

In tissues poorly perfused with blood Signup and view all the answers

What role does insulin play in glycolysis?

Induces key enzymes of glycolysis Signup and view all the answers

What is the primary product of glycolysis under anaerobic conditions?

Lactate Signup and view all the answers

Which enzyme is NOT one of the three regulatory enzymes of glycolysis?

Pyruvate dehydrogenase Signup and view all the answers

In red blood cells, what is the reason glycolysis is the only source of energy?

They lack mitochondria. Signup and view all the answers

How does insulin affect the glycolytic pathway during fed states?

It activates glycolysis by dephosphorylating key enzymes. Signup and view all the answers

What clinical condition is associated with pyruvate kinase deficiency in red blood cells?

Hemolytic anemia Signup and view all the answers

What is the net energy production from aerobic glycolysis?

8 ATP Signup and view all the answers

Which enzyme complex is responsible for the conversion of pyruvate to acetyl CoA?

Pyruvate Dehydrogenase Complex Signup and view all the answers

Which coenzyme is NOT required for the function of Pyruvate Dehydrogenase?

Vitamin C Signup and view all the answers

What happens to NADH + H produced during glycolysis under aerobic conditions?

It is shuttled to the inner mitochondrial membranes. Signup and view all the answers

What causes allosteric inhibition of the Pyruvate Dehydrogenase Complex?

Elevated levels of acetyl CoA and NADH + H Signup and view all the answers

Which statement about anaerobic respiration in red blood cells is true?

Red blood cells utilize anaerobic respiration even in the presence of sufficient oxygen. Signup and view all the answers

Which of the following conditions could inhibit the Pyruvate Dehydrogenase Complex?

Mercury exposure Signup and view all the answers

What is a significant effect of pyruvate dehydrogenase deficiency?

Severe health effects that may lead to early childhood mortality Signup and view all the answers

What component is essential for the action of the Pyruvate Dehydrogenase Complex?

Lipoic Acid Signup and view all the answers

Which of the following indicates the active form of the Pyruvate Dehydrogenase Complex?

Dephosphorylated form Signup and view all the answers

Study Notes

Cytosolic Respiration

Students will be able to correlate carbohydrate intake to energy production, deduce how energy production differs among cells and compartments, and correlate glycolysis regulation to energy production.

What is Glycolysis?

Glycolysis is a sequence of reactions occurring in the cytoplasm to oxidize glucose to two pyruvic acid molecules (3-carbon) under aerobic conditions, or lactate under anaerobic conditions.
It provides energy (ATP) and intermediates for other metabolic pathways.
Glycolysis is the only source of energy in red blood cells (RBCs) due to a lack of mitochondria, and during physical exertion, for muscle cells.
It is a preliminary step before complete oxidation.
It provides carbon skeletons for amino acid synthesis and glycerol portions of fat.

Preparatory Phase of Glycolysis

Initial phosphorylation of glucose occurs.
Glucose is converted to glucose-6-phosphate and then fructose-6-phosphate. Glucose-6-phosphate and fructose-6-phosphate are irreversible reactions.
Fructose 1,6-bisphosphate is formed from fructose-6-phosphate. This is another irreversible reaction.
Cleavage of 6-carbon sugar phosphate makes two 3-carbon sugar phosphates - glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Dihydroxyacetone phosphate is isomerized to glyceraldehyde-3-phosphate.

Payoff Phase of Glycolysis

Oxidative conversion of glyceraldehyde-3-phosphate to pyruvate.
Coupled formation of ATP and NADH.
First ATP formation reaction (substrate-level phosphorylation)
Second ATP formation reaction (substrate-level phosphorylation)
Finally, pyruvate, is formed.

Net Gain

2 ATP molecules and 2 NADH molecules are produced.

Anaerobic Conditions

Under anaerobic conditions, NADH+H+ are reoxidized via lactate formation. This allows glycolysis to progress without oxygen.

Clinical Implications - Pyruvate Kinase Deficiency

Mature red blood cells are completely dependent on glycolysis for ATP.
Pyruvate kinase deficiency leads to decreased ATP.
This results in hemolytic anemia, requiring regular transfusions.
Severity depends on the degree of enzyme deficiency.

Regulation of Glycolysis

The glycolytic pathway is regulated by 3 irreversible enzymes:
- Hexokinase
- Phosphofructokinase (PFK-1)
- Pyruvate kinase (PK)

Hormonal Regulation

Insulin, secreted during the fed state, activates key glycolysis enzymes by dephosphorylation.
Glucagon, secreted during fasting, inhibits key enzymes of glycolysis by phosphorylation.
Induction/Repression: Insulin leads to the induction, and Glucagon represses glycolytic enzymes.

Allosteric Regulation

Allosteric regulators control enzyme activity without changing its structure.

Inhibitors of Glycolysis

Mercury inhibits glyceraldehyde-3-phosphate dehydrogenase by binding to the enzyme's active site, inhibiting glycolysis and potentially leading to cell death.
Fluoride combines with Mg2+ , impacting enolase activity, which is used for in pesticides and rodenticide.

What Happens To Pyruvate After Glycolysis?

Pyruvate is transported to the mitochondria, converting to Acetyl CoA via the action of the Pyruvate Dehydrogenase Complex.

Aerobic vs. Anaerobic Respiration

Glycolysis occurs in both aerobic and anaerobic conditions, but has differences.
Anaerobic respiration occurs in tissues that are poorly perfused, or during conditions like exercise.
Cells lacking mitochondria or under high oxygen demand, such as exercising muscles, utilize anaerobic respiration.
Under normal oxygen conditions, other tissues undergo aerobic respiration.
Aerobic respiration in cells that use it produce more ATP from glucose (38 ATP total) than anaerobic cells (2 ATP).
NADH produced by glycolysis will be used by the LDH enzyme.

What Happens if Glycolysis Occurs In Aerobic Cells?

If glycolysis occurs in aerobic cells, two NADH+H+ molecules are produced.
These are shuttled to the inner mitochondrial membranes where they're fully oxidized.
This produces three ATP each, which, combined with the 2 ATP net from glycolysis, generates 8 ATP in total.

How is NADH+H+ Produced in the Cytoplasm Transported to the Mitochondria?

The inner mitochondrial membrane lacks a NADH transporter.
NADH must be transported through shuttle systems (e.g., glycerol 3-phosphate shuttle, malate-aspartate shuttle).

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Description

Test your understanding of glycolysis and the effects of various compounds on this critical metabolic pathway. Explore questions about glucagon, fluoride interference, aerobic respiration, and anaerobic conditions. Perfect for students of biochemistry and related fields.