Pack 16 - Photosynthesis and Respiration

ATP
1. ADP + Pi --> ATP + H2O
  1. Catalysed by ATP synthase
    1. Reverse reaction catalysed by ATP hydrolase
Coenzymes
1. These are molecules that some enzymes need so they can function.
2. e.g. NAD and NADP
Oxidation is the loss of electrons and H+
1. Reduction is the gain of electrons and H+
Photosynthesis
1. Photoionisation of chlorophyll
  1. When light energy is absorbed by a chlorophyll molecule, its electrons gain energy.
2. The Light Dependant Reaction
  1. This occurs in the thylakoid membrane
  2. The products of this reaction is ATP and NADPH
  3. 1. Light is absorbed by chlorophyll in photosystem II
    1. 2. This absorbed energy causes the electrons to become photoionised
      1. 3. Some light energy is used to split water releasing electrons, protons and oxygen.
        4. Energy released by electrons as they pass between electron carriers is used to transport protons
        5. At the same time, light energy is absorbed by chlorophyll in photosystem I
        6. A pair of electrons is released from the chlorophyll in photoionisation and passes along a series of electron carriers
        7. Photolysis of water and movement of protons means there is a high proton concentration gradient
        8. Protons pass through ATP synthase channel, they cause a change in enzyme shape and catalyse ADP + Pi to ATP
3. The light Independant Reaction
  1. Carbon dioxide for use in the LIR diffuses from:
    1. 1. From the atmosphere
      1. 2. Into leaf through stomata
        3. into water surrounding mesophyll cells
        4. Through cell surface membrane, cytoplasm and chloroplast membrane
        5. Into stroma
4. Factors affecting:
  1. The rate of the process is determined by the factors with the least favourable value
  2. Light: rate is proportional to light intensity
    1. At compensation point, there is no net exchange of gases
      1. After this point, light has no effect
  3. CO2
    1. Optimimum conc. = 0.1%
    2. Conc. affects enzymes
  4. Temp.
    1. Rate is proportional to temp.
    2. 0-25 degrees rate is doubled every 10
Respiration
1. Aerobic
  1. a) Glycolysis
    1. 1. Addition of two phosphate molecules causes phosphorylation of glucose
      1. 2. Phosphorylated glucose is split into two 3C molecules (TP)
        3. Oxidation of TP, hydrogen is removed and transferred to NAD
        4. Production of ATP, each TP molecule is converted to pyruvate, for each of these there are 2 ATP molecules
  2. b) The Link Reaction
    1. Takes place in the mitochondria
    2. 1. Pyruvate enters the mitochondria by active transport
      1. 2. Pyruvate is oxidised to acetate (2C) losing a carbon dioxide moilecule and two hydrogens.
        NAD is a hydrogen acceptor
        3. Acetate (2C) combines with coenzyme A to form acetylcoenzyme A
  3. c) The Kreb's cycle
    1. 1. Acetate (2C) from acetyl coenzyme A combines with a 4C molecule to produce a 6C molecule
      1. 2. 6C molecule loses two CO2 and a hydrogen molecule that form a 4C molecule, Single ATP molecule is produced
        3. 4C molecule now combines with new acetate molecule to form acetylcoenzyme A
    2. 2C
  4. d) Electron Transfer Chain (ETC)
    1. 1. In glycolysis, link reaction and the Krebs cycle, protons produced combine with the coenzymes NAD and FAD to make NADH and FADH
      1. 2. NADH's donate electrons of the protons to the first molecule in the ETC
        3. Electrons pass long a chain of electron transfer molecules
        Oxidation + reduction occur
        Energy released by electrons moving allow the transport of protons from matrix to inter membrane space
        4. Protons flow through ATP synthase from a high conc. to a low conc.
        5. This causes a change in shape of ATP synthase and so ATP is produced
        6. 4 electrons, 4 protons and two molecules of Oxygen reaction to form two molecules of water.
        Oxygen is the final electron acceptor
        Without oxygen, there is nothing to accept the electron
        So electrons cannot pass through
        This means NADH cannot give up its electron
        And so there is no NAD to pick up more protons from the Krebs cycle
        If ATP synthase is bypassed, heat is likely produced
    2. Or oxidative phosphorylation
2. Anaerobic
  1. Without oxygen present, all NAD and FAD is used up, and there is no oxygen to remove the protons or electrons
    1. So Link, Krebs and ETC cannot occur
  2. The only energy source is from glycolysis (2 ATP molecules)
  3. In plants and microorganisms:
    1. Pyruvate loses a carbon dioxide molecule and accepts protons fom NADH, so NAD is regenerated and can accept more protons form glycolysis
  4. In animals:
    1. Pyruvate accepts protons from NADH. So NAD can return to glycolysis to accept more protons

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Pack 16 - Photosynthesis and Respiration

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	Created by Jacob Shepherd about 8 years ago