Overview of Metabolism

Key Topics Covered

• Glycolysis
• Glycogenesis
• Glycogenolysis
• Gluconeogenesis
• Krebs Cycle
• Electron Transport Chain
• Lipogenesis
• Lipolysis
• Ketogenesis
• Ketolysis

Introduction

• The lecture covers key metabolic processes assessed in biochemistry exams.
• Focus on macronutrients: carbohydrates, proteins, triglycerides.
• Macronutrients are broken down into glucose, amino acids, glycerol, and fatty acids.

Breakdown of Macronutrients

• Carbohydrates: Composed of carbon, hydrogen, and oxygen. Broken down into glucose.
• Proteins: Composed of carbon, hydrogen, oxygen, and nitrogen. Broken down into amino acids by pepsin.
• Triglycerides: Composed mostly of carbon, hydrogen. Broken down into glycerol and fatty acids by lipases.

Absorption and Transport

• Glucose and amino acids absorbed into the bloodstream via the portal system to the liver.
• Glycerol and fatty acids absorbed into the lymphatic system and eventually reach the liver.

Metabolic Processes

Glucose Metabolism

• Glycogenesis: Storage of glucose as glycogen in the liver.
• Glycogenolysis: Splitting glycogen to release glucose.
• Glycolysis: Conversion of glucose into pyruvate.

Pyruvate Pathway

• Pyruvate enters mitochondria, transforms into acetyl-CoA.
• In mitochondria, acetyl-CoA enters the Krebs Cycle (Citric Acid Cycle or TCA Cycle).
• The purpose: production of NADH and FADH2 for the Electron Transport Chain.

Electron Transport Chain

• NADH and FADH2 donate electrons, creating a proton gradient.
• ATP is synthesized via ATP synthase driven by this gradient.
• Requires oxygen for oxidative phosphorylation.

Anaerobic Conditions

• In absence of oxygen, pyruvate is converted to lactate, not releasing hydrogen ions.
• Lactate can convert back to pyruvate when oxygen is available.

Alternative Metabolic Pathways

Amino Acids

• Do not have a storage form; excess deaminated and excreted as urea.
• Can enter glycolysis or Krebs Cycle for energy production.

Glycerol and Fatty Acids

• Glycerol can enter glycolysis.
• Fatty acids can enter Krebs Cycle as acetyl-CoA.

Ketogenesis and Ketolysis

• Ketogenesis: Acetyl-CoA converts to ketones in absence of glucose.
• Ketolysis: Ketones converted back to acetyl-CoA in the brain.

Gluconeogenesis

• Formation of new glucose from non-carbohydrate sources (amino acids, glycerol).

Lipid Metabolism

• Lipogenesis: Formation of triglycerides from excess glycerol and fatty acids.
• Lipolysis: Breakdown of triglycerides back into glycerol and fatty acids.

Summary

• The lecture provides a comprehensive overview of metabolic pathways crucial for understanding biochemistry exams.
• Emphasis on the interplay between different biochemical processes in the body.