Metabolism Overview in Biochemistry

Metabolism

• Metabolism is the sum total of all biochemical reactions in a living organism.
• It's the central theme in biochemistry, keeping cells and organisms alive and providing energy for growth and propagation.
• Animal and human metabolism is conceptually divided into catabolic and anabolic reactions.

Types of Metabolism

1. Catabolism

• Catabolism involves breaking down large biochemical molecules into smaller ones.
• This process typically releases energy.
• The oxidation of glucose is a catabolic reaction.
• Key roles of catabolic reactions include: producing energy (ATP), reducing power (NADPH), and regenerating building blocks for anabolic reactions.

2. Anabolism

• Anabolism involves joining small biomolecules to form larger ones.
• Anabolic reactions typically require energy.
• The synthesis of proteins from amino acids is an example of an anabolic process.
• Catabolism and anabolism are opposite reactions; one releases energy, the other consumes it.
• Reactions are often organized into metabolic pathways.

Metabolic Pathways

• A metabolic pathway is a series of consecutive biochemical reactions that convert a starting material into an end product.
• Glycolysis, also called the Embden-Meyerhof Pathway, is a major pathway for carbohydrate catabolism, starting with glucose.
• It's an anaerobic process, meaning it doesn't require oxygen.

Glycolysis

• Glycolysis can be divided into two main segments:

• Investment of ATP: Without an initial ATP investment, glucose doesn't have enough energy for glycolysis to proceed, and ATP isn't produced. This involves the first 5 reactions of glycolysis.

• Net energy yield: This includes the subsequent reactions in glycolysis, producing a net energy gain.

• Glycolysis involves 10 steps, including reactions with specific enzymes.

  • This includes reactions for Glucose, Glucose-6-phosphate, Fructose-6-phosphate, Fructose-1,6-biphosphate, DHA phosphate + Glyceraldehyde-3-phosphate, Glyceraldehyde-3-phosphate, 1,3-biphosphoglycerate, 3-phosphoglycerate, 2-phosphoglycerate, Phosphoenolpyruvate, and ATP Production.

• Note: Reactions 6-10 occur twice per glucose molecule because the initial, six-carbon glucose is split into two 3-carbon molecules, generating 2 NADH and a total of four ATP molecules in the process.

• The net ATP gain is only two, but there was an investment of two ATP molecules earlier in the process in the initial reactions, and that investment is paid back.

Conversion of Pyruvate to Acetyl CoA

• Under aerobic conditions, glucose can be completely oxidized to produce CO2.
• This happens in a pathway called the Citric Acid Cycle (TCA cycle) or Krebs cycle.
• Pyruvate, entering the mitochondria, is converted to a two-carbon acetyl group.
• This acetyl group is ‘activated' to join the TCA cycle when bonded to coenzyme A.
• CoA is derived from ATP and pantothenic acid; Acetyl CoA is the activated form of the acetyl group.

Overview of Biochemical Energy Production

• Energy production from food occurs in four major stages:
• Digestion: Breaking down food into smaller molecules (glucose, amino acids, fatty acids).
• Acetyl group formation: Small molecules from digestion are oxidized in the cytosol and mitochondria. This creates two-carbon acetyl units that attach to coenzyme A, along with reduced coenzyme NADH..
• Citric Acid Cycle: Acetyl CoA is oxidized in the mitochondria, producing ATP, NADH, and FADH2
• Electron Transport Chain and Oxidative Phosphorylation: NADH and FADH2 (from previous stages) supply fuel for producing ATP through a series of reactions that use oxygen.

General Metabolic Pathways

• Glucose, lipids and proteins undergo specific metabolic pathways that ultimately generate energy.
• The relevant stages in metabolism, for example, involve glycolysis (glucose metabolism), B-Oxidation (lipid breakdown), and oxidative deamination of proteins (releasing amino acids).
• These pathways often intersect and connect within the wider metabolic process.

Explore the fundamental concepts of metabolism, including the key processes of catabolism and anabolism. Understand how these biochemical reactions contribute to energy production and the overall maintenance of life in organisms. This quiz will test your knowledge of these critical biochemical themes.