adv nutrition and metabolsim lecture 12

Introduction

  • Discussing metabolic pathways related to glucose synthesis and breakdown.

  • Importance of understanding concepts instead of copying answers.

Key Concepts of Glucose Metabolism

  • Pathways: Understanding terms like lysis (breaking down) and genesis (synthesis).

    • Glycogenesis: Synthesis of glycogen from glucose.

    • Glycolysis: Breakdown of glucose to pyruvate.

Glycolysis

  • Process: Glucose is converted to pyruvate through a series of enzymatic reactions.

  • End Product: Pyruvate, represented as C3H4O3.

  • Deprotonation: Under physiological pH, pyruvate can lose a proton, resulting in its deprotonated form, C3H3O3.

Glycogenolysis

  • Definition: Breakdown of glycogen to glucose.

  • Involves enzymes that facilitate the conversion of glycogen to glucose.

Glucose Transport

  • Transporters: GLUT2 is a key glucose transporter.

    • Glucose enters cells through the action of transporters.

    • Phosphorylation: Conversion of glucose to glucose-6-phosphate.

      • Enzyme involved: Glucokinase (in liver) and Hexokinase (in muscles).

Enzyme Specificity and Action

  • Hexokinase vs. Glucokinase:

    • Hexokinase: Found in muscles; inhibited by high glucose-6-phosphate concentrations.

      • Efficient at low glucose concentrations.

    • Glucokinase: Found in the liver; not inhibited by glucose-6-phosphate.

      • Active at high glucose concentrations, promoting glycogen storage.

Insulin's Role in Glucose Metabolism

  • Insulin Function: Facilitates the uptake of glucose into cells, particularly in the liver and muscles.

  • Type 2 Diabetes: In insulin-resistant individuals, glucokinase activity decreases, leading to difficulty in metabolizing glucose.

Glycogenesis and Glycogen Storage

  • Glycogen Storage:

    • Liver stores about 7% of its weight in glycogen; muscle stores approximately 500 grams.

    • Liver glycogen can be released into the bloodstream to maintain glucose levels, particularly during fasting.

  • Functionality of Muscle Glycogen:

    • Utilized for energy within muscle fibers, cannot directly contribute to blood glucose levels.

Enzymatic Reactions in Glycogenesis

  • Phosphorylase Enzyme: Important in the synthesis of glycogen.

    • UDP glucose is a key component in glucose storage reactions.

  • Enzymes and substrates must be present to facilitate glucose conversion.

Conclusion

  • Understanding metabolic pathways is crucial for exams on metabolism. Reviewing these pathways helps to grasp the complexities of glucose metabolism.