Metabolism and Catabolism

• Metabolism is the process where carbs, lipids, and proteins are broken down
• It is the total sum of all chemical reactions in living cells
• Anabolism builds more complex compounds
• Catabolism breaks down complex compounds

Glycolysis

• Aerobic pathways occur when O2 is available
• Produces ~36 ATP
• This process is slow and uses CHO, Pro, and Fat for fuel
  • Glycogen to Glucose is reversible and doesn't require O2
  • Glucose to Pyruvate is glycolysis, and doesn't require O2
  • Pyruvate to Acetyl CoA is irreversible, and requires O2
• Anaerobic pathways occur when O2 isn't available, often during exercise
• It only makes 2 ATP and happens rapidly
• It uses glucose as fuel and will eventually run out
  • Glucose to Pyruvate to Lactate

Catabolism Examples

• Glucose: Glucose → Pyruvate → Acetyl CoA → TCA cycle → ETC
• Lipids: Glycerol → Pyruvate or Fatty Acids → Acetyl CoA
• Proteins: Amino Acids → Pyruvate / Acetyl CoA / TCA Cycle
• Pyruvate can be converted back to glucose
• Acetyl CoA cannot be converted back to glucose
• Fatty Acids cannot be converted back to glucose
• Carbs, fat, and protein can be stored as fat

Fasting

• During fasting, glycogen and fatty acids are broken down
• Glycerol and amino acids are used to make glucose
• This suppresses appetite and slows metabolism