Pyruvate and Energetics of Glycolysis

C483 Spring 2013

1. The conversion of pyruvate to ethanol also causes the ________. A) oxidation of NADH B) production of ADP C) consumption of O2 D) generation of an ion gradient across mitochondrial membranes

2. The enzyme that catalyzes the conversion of pyruvate to lactate is ________. A) lactate reductase B) pyruvate kinase C) lactoenolpyruvate D) lactate dehydrogenase

3. Which fate of pyruvate is an anaerobic process?A) Formation of alanineB) Formation of oxaloacetateC) Formation of acetyl CoAD) Formation of lactate

Seven of the ten reactions in the glycolytic pathway have free energy values close to zero. What does this tell us about those reactions? A) They are near equilibrium reactions. B) They are not control points for pathway regulation. C) They are reversible reactions. D) All of the above.E) None of the above.

Which of the following is false concerning steps 1, 3, and 10 of glycolysis?A) All are catalyzed by a kinase.B) All involve ATP hydrolysisC) All have a negative standard free energyD) All have a negative free energy under cellular conditionsE) All are irreversible steps.

Fate of Pyruvate

Gluconeogenesis

Amino acidand nitrogenmetabolism

Aerobic Energy

Anaerobic inmicroorganisms

Anaerobic inhigher organisms

The Problem of Anaerobic Metabolism

• With oxygen, the NADH produced in glycolysis is re-oxidized back to NAD+

• NAD+/NADH is a co-substrate which means…• If there is no oxygen, glycolysis will stop

because…• The solution to the problem is to…

The solution in Yeast• Pyruvate is decarboxylated

(cofactor?) to acetaldehyde• Acetaldehyde transformed to

ethanol – What type of reaction?– What cofactor?

• NAD+ is regenerated to be reused in GAPDH

Balanced Anaerobic Equation

Glycolysis:

+

Ethanol:______________________________

The Solution in Us

• Lactate formation

• Balanced equation

• Do the same exercise as yeast

Overall Energetics of Glycolysis

• Standard Free energy change, and standard free energy change at 37o with ions

• Problem?

Actual Free energy

• Irreversible reactions: Which type of enzymes?

• Near-equilibrium reactions

• Notice: reactions 5 and 6 together

Answers

1. A2. D3. D4. D5. B