Metabolism

• Definition: The balance of all anabolic (synthesis) and catabolic (decomposition) reactions in the body.

Anabolic Reactions

• Function: Synthesize complex molecules from small molecules.
• Energy Requirement: These reactions require energy, termed as endergonic processes.

Catabolic Reactions

• Function: Breakdown complex organic compounds.
• Energy Production: These reactions provide energy, known as exergonic processes.
• Examples: Includes glycolysis, Krebs cycle, and electron transport.

Energy and Metabolism

• ATP (adenosine triphosphate) is the molecular unit of currency for energy transfer in cells.
• Metabolic Reactions:
  • ATP is formed during metabolism, serving as an energy coupling between anabolic and catabolic reactions.

ATP Characteristics

• Each cell has approximately 1 billion ATP molecules that typically last for less than one minute.
• More than half of the energy released from ATP is converted into heat.

Energy Transfer Mechanisms

Energy Storage

• Energy is stored in the chemical bonds between atoms.

Oxidation and Reduction

• Oxidation: Refers to a decrease in the energy content (specifically, a loss of electrons) of a molecule.
• Reduction: Refers to an increase in the energy content (specifically, an addition of electrons) of a molecule.
  • Illustration of Reduction:
    • Original: $COOH$
    • After reduction: $H-C-OH$
    • Add 2 H ( ext{H}^+ + ext{H}^{-}) resulting in: $CH_3$
    • Example: Pyruvic acid can be converted to lactic acid through reduction.

Coupling of Oxidation-Reduction Reactions

• Oxidation-reduction (redox) reactions are always coupled in the body. Whenever one substance is oxidized, another substance is almost simultaneously reduced.

Mechanisms of ATP Generation

• Phosphorylation: The process of forming ATP from ADP and inorganic phosphate (Pi)
  • Reaction: ADP + Pi
    ightarrow ATP
  • Energy storage occurs in the bond attaching the second and third phosphate groups.

Types of Phosphorylation

1. Substrate-Level Phosphorylation: Occurs in the cytosol of cells.
2. Oxidative Phosphorylation: Takes place in mitochondria.
3. Photophosphorylation: Found in chlorophyll-containing plants or bacteria.

Macromolecules of Life

• Proteins: Long 3-dimensional chains of amino acids.
• Carbohydrates: Polysaccharides defined as chains of monosaccharides.
• Lipids: Composed of chains of triglycerides.
• Nucleic Acids: Include DNA and RNA, which are essential for storage and expression of genetic information.