Carbohydrate Metabolism and Gluconeogenesis

Introduction

Key Concept: Our body maintains a narrow and constant range of blood glucose (60-150 mg/dL).
Contrast: Fatty acids can vary nearly tenfold, while blood glucose remains stable.
Importance of Glucose: Certain tissues (brain, eyes, kidneys, red blood cells) rely almost exclusively on glucose for ATP production.

Purpose: Use glucose to produce ATP.
Steps:
1. Glycolysis: Breakdown of glucose.
2. Krebs Cycle: Further oxidation of glucose products.
3. Electron Transfer Chain: Produces bulk ATP.

Example: Eating a chocolate chip cookie.
Process: Glucose from the GI tract enters the bloodstream directly and is used by cells.

Need: Body needs to pump glucose into the blood to maintain levels.
Methods:
1. Glycogen Breakdown:
  - Storage: Glycogen is stored mostly in the liver.
  - Duration: Lasts about 10-18 hours.
2. Gluconeogenesis:
  - Definition: Creation of new glucose from non-carbohydrate sources.
  - Precursors: Amino acids and lactate.
  - Purpose: Maintains blood glucose concentration and ATP supply during prolonged fasting.

Stages:
- Starts with Glucose.
- Produces glyceraldehyde 3-phosphate.
- Ends with Pyruvate.

Process: Nearly the reverse of glycolysis.
Challenges: Some steps in glycolysis are irreversible (negative ΔG).
Solutions:
- Reversible Steps: Seven reactions with nearly zero ΔG can go both directions.
- Irreversible Steps: Three steps need alternative pathways.

Locations:
- Glucose to Glucose-6-phosphate.
- Second step (specific step not mentioned in transcript).
- Last conversion to Pyruvate.
Problem: Need a negative ΔG for reactions to occur in the reverse direction.
Solution: Different reaction pathways for these steps during gluconeogenesis.

Concept: Gluconeogenesis is the body's method of maintaining glucose levels when not eating.
Big Picture: Produces glucose to be used for ATP production and maintaining blood glucose levels.