topic 5

• Light dependent reactions


  One of two stages in photosynthesis, occurs in the thylakoid membranes (grana)
• Light dependent reactions


  1. Photolysis of water

  2. Photo ionization of chlorophyll

  3. Chemiosmosis
• Photolysis of water


  Light energy splits water into oxygen, electrons, and protons
• Photo ionization of chlorophyll

  Light energy causes chlorophyll to lose electrons, which become excited and are released
• Chemiosmosis


  1. Electrons from photo ionization pass through electron transport chain, releasing energy to pump protons into thylakoid lumen

  2. Protons flow back through ATP synthase, providing energy to produce ATP

  3. Protons also reduce NADP to NADPH
• Oxygen produced from photolysis of water is a waste product of photosynthesis
• NADPH and ATP produced in light dependent reactions are needed for the light independent reactions
• The light dependent reactions occur in the thylakoid membranes (grana) of the chloroplast
• The light dependent reactions require light energy
• The light dependent reactions produce ATP and NADPH
• Light independent reaction


  Also known as the Calvin cycle
• Light independent reaction


  • Occurs in the chloroplast, in the fluid center called the stroma
  • Enzyme rubisco catalyzes a key stage
• Unlike the light dependent reaction

  Temperature does affect the rate of reaction of the Calvin cycle
• Key molecules involved in the Calvin cycle

  • Carbon dioxide
  • Reduced NADP
  • ATP
• Calvin cycle


  1. Carbon dioxide reacts with rubp (ribulose bisphosphate)

  2. Produces two molecules of gp (glycerate 3-phosphate)

  3. gp converted to tp (triose phosphate) using ATP and reduced NADP

  4. One carbon atom removed from tp each cycle

  5. Remaining 5 carbons used to regenerate rubp using ATP
• Organic substances


  Substances which contain carbon, including glucose, disaccharides, polysaccharides, lipids
• Limiting factors


  • Anything that could reduce the rate of photosynthesis, including temperature, carbon dioxide concentration, light intensity
• At low levels of a limiting factor


  That factor is the limiting factor
• At high levels of a limiting factor


  That factor is no longer limiting, another factor becomes limiting
• Knowing about limiting factors allows farmers to manipulate conditions to optimize plant growth, but they must consider the cost-effectiveness
• Glycolysis


  The first stage of aerobic respiration that happens in the cytoplasm
• Aerobic respiration


  The process of producing ATP using oxygen
• Glycolysis is also part of anaerobic respiration
• Glycolysis


  1. Phosphorylation of glucose

  2. Splitting of glucose phosphate into two triose phosphate

  3. Oxidation of triose phosphate to pyruvate
• Phosphorylation


  Adding a phosphate group to a molecule
• Two ATP are used in the phosphorylation of glucose
• Glucose phosphate is a high-energy, highly reactive molecule
• Triose phosphate


  A three-carbon sugar with a phosphate group attached
• Triose phosphate is oxidized to form pyruvate
• The oxidation of triose phosphate produces a net gain of 2 ATP
• NADH


  The reduced form of the coenzyme NAD, produced when triose phosphate is oxidized
• The NADH produced in glycolysis will be used in the final stage of aerobic respiration, oxidative phosphorylation
• Aerobic respiration


  1. Glycolysis

  2. Link reaction

  3. Krebs cycle

  4. Oxidative phosphorylation
• Glycolysis


  First stage of aerobic respiration, anaerobic and aerobic
• Link reaction


  1. Pyruvate oxidized into acetate

  2. Hydrogen from pyruvate picked up by NAD, reducing it to NADH

  3. Acetate converted into acetyl coenzyme A
• Link reaction


  • Products: acetyl coenzyme A, carbon dioxide, reduced NAD
• Krebs cycle


  1. Acetyl coenzyme A reacts with 4-carbon molecule to form 6-carbon molecule

  2. Series of redox reactions reducing NAD and FAD, releasing 2 carbon dioxide

  3. Produces ATP
• Krebs cycle


  • Products per cycle: 3 reduced NAD, 1 reduced FAD, 1 ATP, 2 carbon dioxide

  Products per glucose: 6 reduced NAD, 2 reduced FAD, 2 ATP, 4 carbon dioxide
• Link reaction and Krebs cycle happen in the mitochondrial matrix
• Oxidative phosphorylation


  1. Electron transfer chain movement

  2. Proton transport across inner mitochondrial membrane

  3. ATP synthesis by ATP synthase