Energy and Metabolism

Energy and Metabolism

• Metabolism is the sum of catabolic and anabolic chemical processes.
• Catabolism releases energy (exergonic), anabolism takes up energy (endergonic).
• Proteins break down into amino acids.
• Carbohydrates break down into glucose, fructose, and galactose.
• Fats and lipids break down into fatty acids and glycerol.
• Glycogen breaks down into glucose-6-phosphate.
• Glycolysis converts glucose into pyruvic acid.
• Gluconeogenesis converts noncarbohydrate precursors into glucose.
• Lactic acid is formed during anaerobic respiration.
• Citric acid cycle is a series of reactions where acetyl CoA is broken down.
• Electron transport chain produces a large amount of ATP.
• Synthesis of larger molecules (anabolism) requires energy.
• Proteins are created from amino acids.
• Carbohydrates are synthesized into starch.

Common Intermediate in Metabolism

• Several molecules converge into a common intermediate, acetate (acetyl-CoA).
• This intermediate fuels various anabolic pathways.
• Examples of end products include steroids, hormones, and carotenoids.

Two Phases of Metabolism

• Catabolism occurs through degradative and oxidative, converging pathways.
• Anabolism uses biosynthetic and reductive pathways, diverging in product synthesis.

Energy Currency in Metabolism

• ATP is the energy currency of the cell.
• ADP and AMP are related to energy storage.
• Coenzymes such as NAD+ and FAD accept hydrogen or electrons, which are used in ATP production.

Cellular Respiration: Overview

• Glucose is oxidized to yield energy in the form of ATP.
• The process occurs in three main stages: glycolysis, transition reaction, and citric acid cycle followed by the electron transport chain.
• Glycolysis produces a net gain of two ATPs.
• The transition reaction converts pyruvate into acetyl CoA.
• The citric acid cycle produces CO2 and electron carriers.
• The electron transport chain generates a large amount of ATP from electrons.
• The overall reaction is C6H12O6 + 6O2 → 6H2O + 6CO2 + 36 ATP + heat (AG = -686 kcal/mol).

Glycolysis

• The first stage of glucose catabolism.
• No oxygen required.
• Occurs in the cytoplasm.
• Converts 6C glucose into two 3C pyruvates.
• Produces a small amount of energy (2 ATP).
• Pathway regulated according to cellular needs.

Fate of Pyruvic Acid

• Pyruvic acid from glycolysis is converted to acetyl coenzyme A for the Krebs cycle.
• Occurs in three steps: decarboxylation, oxidation, and formation of acetyl CoA.

Krebs Cycle

• An eight-step cycle that oxidizes acetic acid, generates three NADH+H+ and FADH2, and two CO2 molecules.
• Produces one ATP molecule.
• For each glucose molecule entering, two molecules of acetyl CoA enter the Krebs cycle.

Oxidative Phosphorylation

• Hydrogen ions are pumped across the inner mitochondrial membrane to create a proton gradient.
• Electrons are passed along the electron transport chain to oxygen.
• Diffusion of hydrogen ions back across the membrane via ATP synthase releases energy for ATP production.

ATP Production

• Total net ATP yield: 36 or 38 ATP molecules per glucose molecule (theoretical).
• Exact number can vary depending on the cell type.

Lipid Catabolism

• Lipids are broken down into fatty acids and glycerol.
• Fatty acids undergo B-oxidation to produce acetyl CoA.
• Glycerol enters glycolysis.
• Acetyl CoA is a crucial fuel for the Krebs cycle, which produces ATP.

Protein Catabolism

• Proteins are broken down into amino acids by hydrolysis.
• The amino group is removed via deamination, producing ammonia.
• The remaining molecules enter the Krebs cycle for energy generation.
• The ammonia is converted to urea for excretion.

Cori Cycle

• The liver and muscles work together in the Cori cycle to recycle lactic acid.
• Lactic acid produced by muscles during anaerobic respiration is transported to the liver, where it is converted back into glucose.
• This glucose is then transported back to the muscles for use in energy production.