Amino Acid Metabolism and Urea Cycle Notes
Oxidation-Reduction Reactions
- Definitions:
- Oxidation: Loss of electron or hydrogen (H) or gain of oxygen (O2).
- Reduction: Loss of oxygen or gain of hydrogen or electron.
- Key Concept:
- Each oxidation reaction corresponds to a reduction reaction.
- Oxidized substance: Loses energy.
- Reduced substance: Gains energy.
- Coenzymes: Act as hydrogen (or electron) acceptors.
- Examples include NAD/NADH, NADP/NADPH, FAD/FADH2.
- Stage 1: Digestion and Hydrolysis
- Breakdown of dietary proteins, polysaccharides, and lipids.
- Stage 2: Degradation
- Further breakdown and some oxidation to smaller molecules (e.g. glucose, fatty acids).
- Stage 3: Oxidation to CO₂
- CO₂, H₂O, and energy (ATP synthesis) produced.
- Products include amino acids, pyruvate, acetyl CoA.
Digestion of Proteins
- Overview:
- Proteins undergo denaturation during cooking, aiding in digestion.
- Proteolytic Enzymes:
- Secreted as inactive forms (zymogens) to prevent autodigestion.
- Types of Proteolytic Enzymes:
- Endopeptidases:
- E.g. Pepsin, Trypsin, act on peptide bonds within the protein (convert proteins into smaller units).
- Exopeptidases:
- Act on the ends of the peptide chains (Carboxypeptidase at carboxyl terminal and Aminopeptidase at amino terminal).
Stomach Digestion
- Key Components:
- Hydrochloric Acid (HCl): Activates pepsin, denatures proteins, but doesn’t break peptide bonds on its own.
- Pepsin Functioning:
- Active at pH ~2, secreted from chief cells as pepsinogen and activated by HCl.
- Rennin (Chymosin):
- Active in infants for milk protein curdling and facilitates protein digestion.
Pancreatic Digestion
- Key Points:
- Optimal pH ~8 due to alkaline bile/pancreatic juice.
- Peptide hormones (Cholecystokinin) stimulate pancreatic juice secretion.
- Key Enzymes in Pancreatic Juice:
- Endopeptidases: Trypsin, Chymotrypsin, Elastase
- Exopeptidases: Carboxypeptidase
- Activation of Trypsin:
- Trypsinogen → Trypsin (via enterokinase), activates other enzymes.