Glycolysis, Krebs Cycle, and other Energy-Releasing Pathways

Learning Goals for Respiration - After these lectures, students will be able to:

All organisms produce ATP by releasing energy stored in glucose and other sugars.

Aerobic respiration - the process by which a cell uses O2 to "burn" molecules and release energy

The reaction: C6H12O6 + 6O2 >> 6CO2 + 6H2O

Note: this reaction is the opposite of photosynthesis

This reaction takes place over the course of four major reaction pathways

Glycolysis (glyco = sugar; lysis = breaking)


NOTE: this process does not require O2 and does not yield much energy


The First Stage of Glycolysis

The first stage of glycolysis

The Second Stage of Glycolysis

The second stage of glycolysis

Oxidation of Pyruvate and the Krebs Cycle (citric acid cycle, TCA cycle)

The Oxidation of Pyruvate to form Acetyl CoA for Entry Into the Krebs Cycle

The conversion of Pyruvate to Acetyl CoA

The Krebs Cycle


Electron Transport Phosphorylation (Chemiosmosis)

Net Engergy Production from Aerobic Respiration



Photosynthesis: 6 CO2 + 6 H2O >> C6H12O6 + 6 O2

Respiration: C6H12O6 + 6 O2 >> 6 CO2 + 6 H2O

Notice that these reactions are opposites - this is important since the earth is a closed system

All life has a set amount of natural materials to work with, so it is important that they all be cycled through effectively and evenly

Energy Yields:

Related Catabolic Processes - Beta Oxidation


A comparison between Plants and Animals


Other Uses for Molecules used in Glycolysis and the Krebs Cycle

Regulation of Glycolysis and the Krebs Cycle