Metabolism & Metabolic Organelles

Overview of Metabolism

  • Metabolism: Sum of all reactions in a cell, involving energy transformation.
  • Anabolism: Requires energy (ATP, NADH) for synthesis of cell structures from simple building blocks (sugars, fatty acids, amino acids).
  • Catabolism: Releases energy by breaking down macromolecules, producing CO2 and H2O.

Respiration

  • Process that releases energy through the breakdown of chemicals in cells.
  • Macromolecules are broken down using O2, yielding CO2 and H_2O.

Photosynthesis

  • Combines catabolic (light) and anabolic (carbon assimilation) reactions.
  • Uses light energy and H2O to assimilate carbon (CO2) into carbohydrates, releasing O_2.

Activated Carrier Molecules

  • ATP: synthesized by adding a phosphate group to ADP; releases energy upon hydrolysis to ADP and inorganic phosphate.
  • NADH and NADPH: carry high-energy electrons and hydrogen atoms for oxidation-reduction reactions; formed when NAD+ and NADP+ pick up two electrons and a proton (H^+).

Metabolic Organelles

  • Mitochondria (Respiration):
    • Double-membrane organelles; inner membrane folded into cristae to increase surface area.
    • Matrix contains metabolic enzymes and mitochondrial DNA (mtDNA).
    • Divide independently via fission.
  • Chloroplasts (Photosynthesis):
    • Double-membrane organelles containing chlorophyll.
    • Stroma contains thylakoids in grana (site of ETC in plants).
    • Stroma contains enzymes for carbohydrate synthesis and plasmid DNA.
    • Divide independently.

Aerobic Respiration

  • Four stages:
    1. Glycolysis: Glucose splits into pyruvate, yielding 2 ATP and 2 NADH.
    2. Oxidation of pyruvate: Pyruvate is oxidized to Acetyl CoA in the mitochondria, releasing CO_2 and forming NADH.
    3. TCA cycle: Acetyl CoA enters the cycle in the mitochondrial matrix, producing NADH, FADH2, ATP, and CO_2.
    4. Electron transport chain (ETC) and chemiosmosis: Electrons from NADH and FADH2 are passed through protein complexes in the mitochondrial membrane, creating a proton gradient that drives ATP synthesis.
  • Redox Reactions: Transfer electrons; oxidation is loss, reduction is gain.

Anaerobic Respiration

  • Occurs without oxygen; glycolysis continues, and NAD+ is replenished by fermentation.
  • Examples: Pyruvate to lactate in animal cells, pyruvate to ethanol in yeast cells.

Photosynthesis

  • Two phases:
    1. Light reactions: Occur in thylakoid membranes; chlorophyll absorbs light, exciting electrons; water is split (photolysis), releasing oxygen; ATP and NADPH are produced.
    2. Carbon assimilation (Calvin Cycle): Occurs in the stroma; uses ATP and NADPH to convert CO_2 into sugar phosphates.

Collaboration of Chloroplasts and Mitochondria

  • In plants, chloroplasts and mitochondria collaborate to supply cells with metabolites and ATP.

Key Concepts

  • Metabolism is the sum of chemical processes in a cell.
  • Respiration involves redox reactions and electron transfer to generate ATP.
  • ATP synthesis is linked to electron transfer via chemiosmosis.
  • Photosynthesis converts light energy into chemical energy, producing carbohydrates.
  • Organisms can respire without oxygen through anaerobic respiration (fermentation).