Lecture 13: Cellular Respiration: Glycolysis and Citric Acid Cycle

Glucose Requirements of Human Body

CNS and RBCs rely on glucose as energy sources

- preferred substrate

- human body: 160g daily

- human brain: 120g

- bodily fluids: 20g

- glycogen stores: 190g

Glycolysis

10 enzymatic reactions that convert glucose to pyruvate

- phase I and phase II

Starting Material

glucose

- 6 carbon ring

- GLUT receptors facilitate uptake

- once in the cell, ATP traps it

Phase I Glycolysis

energy investment

- two ATP are used to breakdown glucose

- one glucose converts into two GDP3

Phase II Glycolysis

four ATP are generated in the process of making two pyruvate

- generates 2 NADH and 2H+

- 2 pyruvate starting material for citric acid cycle

Glycolysis Inputs and Outputs

input: glucose

outputs: 2 pyruvate, 2 ATP, 2 NADH

Pyruvate Oxidation

bring pyruvate from the cytoplasm into the mitochondria

- CO2 is released and 2pyruvate is converted into 2 coenzyme A before entering citric acid cycle

- this yields 1 NADH per pyruvate (2 NADH per glucose molecule)

Citric Acid Cycle Steps

eight steps, each catalyzed by specific enzyme

- begins when acetyl-CoA reacts with oxaloacetate to form citrate and CoA

- next seven steps decompose citrate back to oxaloacetate

- NADH and FADH2 produced by the cycle relay electrons extracted from food to electron transport chain

Citric Acid Cycle

completes breakdown of pyruvate to CO2

- each turn of cycle oxidizes molecules derived from one pyruvate

- turns twice

- generates 2 ATP, 6 NADH, and 2 FADH2 per glucose molecule

Pyruvate Oxidation and Citric Acid Cycle Inputs and Outputs

inputs: 2 pyruvate > 2 acetyl coA > 2 oxaloacetate > citric acid cycle

outputs: 2 ATP, 6 CO2, 8 NADH, 2 FADH2