BIOL202 Lesson 6

• Fuels provide energy by doing what?

  Breaking chemical bonds
• Combustion

  1. Oxygen (O₂) is released

  2. Carbon dioxide (CO₂) and water (H₂O) are produced

  3. Carbon-hydrogen (C-H) bonds are broken
• First law of thermodynamics

  Energy can never be created or destroyed, it can only change from one form to another
• Second law of thermodynamics

  Conversion of energy is never perfect, energy is transformed into different forms
• In combustion, chemical energy

  Is transformed into heat and light energy
• Cellular respiration

  Harvests chemical energy from food and transforms it into portable chemical energy (ATP) to deliver energy when and where needed
• Adenosine Triphosphate (ATP)


  A type of nucleotide that contains 3 phosphate groups, energy is released when it releases a phosphate group (ATP becomes ADP)
• Everything we eat comes from plants, which generate food molecules using energy from sunlight through photosynthesis
• What are the two stages of photosynthesis?

  1. Energy capture stage (light/photo reaction)

  2. Carbon capture stage (Calvin cycle/synthesis reaction)
• Photosynthetic organisms

  • Prokaryotes: bacteria, cyanobacteria
  • Eukaryotes: plants, fungi
• Structure of chloroplast

  • Thylakoid membrane: contains chlorophyll
  • Thylakoid lumen
  • Stroma: fluid around thylakoid (site of Calvin cycle)
• Chlorophyll pigments

  Absorb energy from light, energy is captured and converted into storage molecules ATP and NADPH (high energy electron carrier for photosynthesis)
• Components of light reaction

  • Photosystems: capture light energy
  • Electron transport chain: releases energy used to generate ATP and NADPH
• Carotenoid pigments allow capture of a wider range of light energy (only pigment that can't be captured is green)
• Light reaction

  1. Light "excites" electrons in chlorophyll, which then return to lower energy state by releasing energy

  2. This energy is passed to a reaction center and then to the electron transport chain
• Oxygen (O₂) is generated as a by-product of the light reaction
• Calvin cycle (carbon capture stage)


  Series of chemical reactions that incorporate CO₂ into organic molecules (sugar)
• What is the Calvin cycle?

  Synthesis part of photosynthesis; ATP, NADPH and CO2 are synthesized to produce sugar
• Cellular respiration

  Energy is released by the breakdown of sugar, used to generate ATP
• Stages of cellular respiration

  1. Glycolysis (in cytosol)

  2. Acetyl-CoA production (in mitochondria)

  3. Krebs cycle (in mitochondria)

  4. Electron transport chain (on inner mitochondrial membrane)
• Glycolysis

  Universal energy-releasing pathway that breaks down glucose into pyruvate, producing 2 ATP and 2 NADH
• Acetyl-CoA production

  Pyruvate is converted into acetyl-CoA, producing 1 NADH and 1 CO₂
• Krebs cycle


  Series of chemical reactions that further break down acetyl-CoA, producing ATP, NADH and FADH₂
• Electron transport chain

  Located on the inner mitochondrial membrane, uses the energy released from the high-energy carriers NADH and FADH₂ to pump protons (H⁺) from the matrix to the intermembrane space, creating a proton gradient that is used by ATP synthase to generate ATP
• For each NADH molecule, the electron transport chain can produce 3 ATP
• If oxygen is not available, cellular respiration stalls and cells must rely on lactic acid fermentation or ethanol fermentation to produce a small amount of ATP
• Ethanol fermentation occurs in yeast cells when oxygen is limited, converting pyruvate to ethanol and carbon dioxide while recycling NAD⁺
• Food is broken down in the digestive tract and the energy is harvested through cellular respiration, with excess sugar stored as glycogen or fat