Metabolism Lecture Review

Metabolism Overview

• ATP (Adenosine Triphosphate):

  • Adenine, Ribose, Triphosphate. Stores energy in 2nd/3rd phosphate bonds.

  • Produced in cellular respiration and photosynthesis (ATP synthase).

  • Temporary energy storage.

• ADP (Adenosine Diphosphate):

  • Adenine, Ribose, Diphosphate. Has 2 phosphate groups.

  • ADP + Pi (inorganic phosphate)
    ightarrow ATP (energy absorbed from food).

• ATP/ADP Cycle: ATP
  ightarrow ADP + Pi (energy released); ADP + Pi
  ightarrow ATP (energy absorbed).

Photosynthesis

• Equation: 6CO2 + 6H2O \xrightarrow{\text{light}} C6H{12}O6 + 6O2

• Organisms: Plants, algae, cyanobacteria, photoautotrophs.

• Electron Carrier: NADPH. Electron Acceptor: NADP+.

• Light-Dependent Reactions (Thylakoid Membrane):

  • Photosystem II (PSII): Light energy splits H2O into protons (H), electrons, and O2.

  • Electron Transport Chain (ETC): Electrons create a proton gradient (active transport).

  • Photosystem I (PSI): Electrons re-energized by light; NADP+ accepts electrons to form NADPH.

  • ATP Synthase: Proton gradient energy drives ADP + Pi
    ightarrow ATP.

• Light-Independent Reactions (Calvin Cycle):

  • Carbon Fixation: RuBP (5-carbon) combines with CO_2 to form an unstable 6-carbon compound, which splits into two 3-carbon compounds. Converts inorganic carbon into organic compounds.

Cellular Respiration

• Equation: C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + \text{ATP}

• Types:

  • Aerobic Respiration: Requires oxygen (e.g., ETC, Krebs cycle).

  • Anaerobic Respiration: Does not require oxygen (e.g., Glycolysis, Fermentation).

• Organisms: Plants, animals, fungi, protists, most bacteria.

• Electron Carriers: NAD+, FAD, O_2.

• Glycolysis (Cytoplasm, Anaerobic): Glucose
  ightarrow 2 G3P (net 2 ATP)
  ightarrow 2 Pyruvate (produces 4 ATP, reduces NAD+ to NADH).

• Prep for Krebs Cycle (Inner Membrane Space, Aerobic): Pyruvate
  ightarrow Acetyl CoA (releases CO_2, reduces NAD+ to NADH).

• Krebs Cycle (Matrix, Aerobic): Releases CO2, produces ATP, and reduces NAD+ to NADH and FAD to FADH2.

• Electron Transport Chain (Cristae/Inner Membrane Folds, Aerobic):

  • NADH and FADH_2 donate electrons.

  • Electrons move through protein channels, creating a proton gradient.

  • ATP Synthase: Proton gradient energy drives ADP + Pi
    ightarrow approx. 36 ATP.

  • Electrons, protons, and O2 combine to form H2O.

Fermentation (Anaerobic Respiration)

• Definition: Cellular respiration without oxygen.

• Lactic Acid Fermentation:

  • Occurs in animals and bacteria.

  • Produces lactic acid and NAD+.

• Alcoholic Fermentation:

  • Occurs in yeast.

  • Produces ethanol, CO_2, and NAD+.