5.2 Glycolysis- Cellular Respiration

Reactants in Glycolysis

Glucose + 2 NAD+ + 2 ADP

Products in Glycolysis

2 Pyruvate + 2 ATP + 2 NADH + 2H2O

2 types of Phosphorylation in Cellular Respiration

1. Substrate- Level Phosphorylation

2. Oxidative Phosphorylation

Substrate- level Phosphorylation

• Enzyme- catalyzed formation of ATP

• Direct transfer of a phosphate group to ADP from a intermediate substrate

Oxidative Phosphorylation

• Formation of ATP using energy derived from the reactions of an electron transport chain

Is glycolysis aerobic or anaerobic

• Anaerobic

Purpose of Glycolysis

• Provide pyruvate for the citric acid cycle

1st Important Step in Glycolysis

• Glucose to Glucose 6- Phosphate

Glucose to Glucose 6- Phosphate

1. Hexokinase uses 1 ATP to convert

   glucose ➞ glucose 6-phosphate, making glucose negatively charged and preventing its diffusion out of the cell.

2nd Important Step in Glycolysis

Phosphofructokinase

Phosphofructokinase

(PFK) uses 1 ATP to convert

fructose 6-phosphate ➞ fructose 1,6-bisphosphate, committing the molecule to glycolysis (irreversible, key regulatory step).

- High ATP inhibits PFK, preventing glycolysis.

- Low ATP disinhibits PFK, promoting glycolysis.

High ATP inhibits…

PFK, preventing glycolysis.

Low ATP disinhibits…

PFK, promoting glycolysis.

Glycolysis’s 2 phases

1. Initial Investment phase

2. 2nd payoff phase

Initial Investment phase

• 2 ATP invested

Payoff phase

• 4 ATP

• 2 NADH produced

• 2 net ATP produced in glycolysis

Recap of Glycolysis

• Overall: Taking 6 C molecules of glucose and making 2×3 C molecules of pyruvate

• Net Production of:

  - 2 ATP

  • 4 are produced, however, 2 were utilized during glycolysis

• 2 molecules of pyruvate

• 2 molecules of NADH

  • NADH is an electron carrier useful for later steps of cellular respiration

  • Note that we need NAD+ to be available to proceed with glycolysis and create NADH