In-Depth Notes on High Energy Transfer and Metabolism

High Energy Transfer and Metabolism

Creatine Phosphate and Energy Production

• Creatine Kinase:
• An enzyme that transfers phosphate groups, converting creatine to creatine phosphate.
• Key to ATP regeneration in muscle cells during high-intensity activity.
• Delta G of Creatine:
• The free energy change when a phosphate group is removed from creatine (-43 kcal/mol) indicates its ability to drive reactions forward.
• Muscle Energy Usage:
• Initial ATP stores are used quickly, followed by creatine phosphate, then anaerobic metabolism, before transitioning to aerobic metabolism for sustained energy production.

Metabolic Pathways and ATP Regulation

• ATP:
• Key energy currency in cells, produced and consumed to fuel biosynthetic activities.
• Metabolic Pathway Overview:
• ATP must be constantly regenerated from ADP, through pathways of fuel oxidation (like glucose, fats).
• Fuel Types:
• Carbohydrates (fast energy), fats (more energy), and proteins (can be used under certain conditions).

Oxidation of Fuels and Energy Yield

• Energy Production:
• Oxidation of fuels leads to carbon dioxide and water as end products of metabolism.
• Varying Energy Yields:
• Different fuels yield varying amounts of energy: fats provide more energy than carbohydrates.
• Electron Carriers:
• Includes NAD+, FAD, and coenzyme A, crucial for transferring electrons and protons during metabolic reactions.

Metabolic Reaction Types

1. Oxidation-Reduction Reactions:

• Involve electron transfer, e.g., succinate to fumarate within the citric acid cycle.

1. Group Transfer Reactions:

• Functional groups (like phosphate) are transferred between molecules. E.g., glucose to glucose-6-phosphate.

1. Hydrolytic Reactions:

• Water is used to break down molecules, e.g., peptide bond hydrolysis.

1. Carbon Bond Cleavage:

• Breaking down larger molecules into smaller ones without water.

1. Isomerization:

• Changes the structure of molecules without altering the molecular formula.

1. Ligation Reactions:

• Forming new bonds using energy from ATP hydrolysis.

Key Molecules in Metabolism

• NAD+ and FAD:
• They serve as electron carriers; their reduced forms store energy (NADH and FADH2).
• Coenzyme A:
• A carrier involved in fatty acid metabolism and synthesis of acetyl CoA, which feeds into the citric acid cycle.

Enzyme Activity and Regulation in Metabolism

• Regulatory Mechanisms:
• Metabolism can be regulated by:
  • Changing enzyme concentration.
  • Modifying substrate accessibility, controlling where substrates can go.
  • Altering catalytic activity, which can involve feedback inhibition or temperature consequences on enzyme activity.
• Enzyme Turnover Rate:
• Must balance the synthesis and degradation rates of enzymes to maintain metabolic homeostasis.

Importance of Vitamins and Coenzymes

• Vitamins:
• Serve as precursors for essential coenzymes, critical for various metabolic pathways. Deficiency can lead to severe health issues.
• Examples:
• Riboflavin → FAD, Niacin → NAD, etc.

Energy Charge of Cells

• Energy Charge Concept:
• A measure of the energy status in a cell, defined by ATP, ADP, and AMP concentrations.
• Ranges from 0 (all AMP) to 1 (all ATP), influencing metabolic reactions and pathways.