6.1-6.2

6.1 Overview of Metabolism

Life’s 2×2 for energy & carbon

  • Energy source

    • Phototrophs: use light (plants, algae, some bacteria)

    • Chemotrophs: use chemicals (food or inorganic fuels; animals, many microbes)

  • Carbon source

    • Autotrophs: make organic C from CO₂ (“self-feeders”)

    • Heterotrophs: get organic C from other organisms (“other-feeders”)

Common combos (know examples)

  • Photoautotrophs = light + CO₂ → sugars (plants, cyanobacteria)

  • Chemoheterotrophs = chemicals + organic C (animals, fungi, most bacteria)

  • Photoheterotrophs = light for energy, organic C for carbon (some aquatic bacteria)

  • Chemoautotrophs = energy from inorganic chemicals, carbon from CO₂ (deep-sea vent microbes)

Note: Even plants break down the sugar they make to power cells (just like animals).

Metabolism = all cell chemistry

  • Catabolism: break big → small (releases energy → ATP)
    e.g., starch → glucose → CO₂ + H₂O

  • Anabolism: build small → big (requires ATP)
    e.g., amino acids → proteins

  • Catabolic ATP pays for anabolic building.

6.2 Kinetic & Potential Energy

Two basic forms

  • Kinetic = motion (moving objects, photons = light, electrons = electricity, molecular motion = heat)

  • Potential = stored (position/structure; ball at top of stairs; ion gradients across membranes)

Energy transforms: potential ↔ kinetic (never created/destroyed).

Chemical energy = potential in bonds

  • Strong covalent bonds (very stable) → low chemical energy

    • Examples: CO₂, H₂O

  • Weaker covalent bonds (less stable) → high chemical energy (good fuels)

    • Lots of C–C and C–H in carbs, lipids, proteins

Breaking bonds needs energy; forming new, more stable bonds releases energy.

ATP: the cell’s quick-spend energy

  • Structure: Adenosine (adenine + ribose) + triphosphate (3 P’s)

  • Why high energy?
    Three negatively charged phosphates repel → bonds between P’s store a lot of potential energy.

  • Use: Cells hydrolyze ATP → ADP + Pi, releasing energy to:

    • power pumps, move molecules/vesicles, drive reactions, contract muscles, etc.

  • Family: ATP (3P), ADP (2P), AMP (1P)

  • Role: middleman between energy-rich fuels (glucose, fats) and cellular work.

Tiny memory aids

  • Photo = light, Chemo = chemicals; Auto = CO₂, Hetero = organic C.

  • Cats break things (catabolism); Ana builds anabolic.

  • More C–H = more fuel.

  • ATP = Ado + Triple Phosphate (triple = energy punch).

  • Exergonic - energy released 

  • Endergonic - energy required, used