General Biology I

Cellular Respiration & Photosynthesis lecture 11


Overview of Cellular Respiration

Process by which living cells obtain energy from organic molecules and release waste products

O2 consumed and CO2 released

Primary aim to make A T P

Aerobic respiration uses oxygen

Anaerobic respiration (fermentation) does not use oxygen


Glucose metabolism

C6H12O6 + 6O2 → 6CO2 + 6H2O

Four metabolic pathways:

  • Glycolysis

  • Breakdown of pyruvate

  • Citric acid cycle

  • Oxidative phosphorylation


Glycolysis

Breakdown of glucose into 2 pyruvates

Glycolysis can occur with or without oxygen

Steps in glycolysis nearly identical in all living species


Three phases:

  • Energy investment

  • Cleavage

  • Energy liberation

Glycolysis – Major Reactions

Net reaction and regulation of glycolysis

  • Rate of glycolysis regulated by availability of substrates and by feedback inhibition


Breakdown of Pyruvate

  • In eukaryotes, pyruvate is transported into the mitochondrial matrix

  • Broken down by pyruvate dehydrogenase

  • Molecule of CO2 removed from each pyruvate

  • Remaining acetyl group attached to CoA to make acetyl CoA

  • Yield = 1 NADH for each pyruvate

Intermediate Step

Breakdown of Pyruvate

Citric Acid Cycle

Metabolic cycle- takes place in the mitochondrial matric (cristae)

Acetyl is removed from Acetyl CoA and attached to oxaloacetate to form citrate (aka citric acid)

Series of steps releases 2 CO2, 1 ATP, 3 NADH, and 1 FADH2

Oxaloacetate is regenerated to start the cycle again

Details of the citric acid cycle

Oxidative Phosphorylation

  • High energy electrons removed from NADH and FADH2 to make ATP in oxidative phosphorylation


  • Typically requires oxygen


  • Oxidative process involves electron transport chain in the inner mitochondria membrane


  • Phosphorylation occurs by ATP synthase