TOPIC 5

TOPIC 5

Aerobic respiration
1. ATP
  1. Energy currency of living cells, as lots of energy is released when hydrolysed
  2. Made by respiration, which is a series of enzyme controlled reactions in which energy is released from organic substances and transferred to ATP
2. Stages of respiration
  1. Glycolysis: glucose to pyruvate
  2. Link reaction: pyruvate to acetyl coenzyme A
  3. Krebs cycle: ACeA enter cyclical reactions
  4. Oxidative phosporylation: ADP converted to ATP
Glycolysis
1. Takes place in cytoplasm
2. Glucose phosphorylated to produce hexose biphosphate, which splits into 2 molecules of glycerate 3-phospate (GP)
  1. Removal of hydrogens = taken by NAD, producing NADH
3. Each GP is converted to pyruvate
  1. Removed phosphate groups added to ADP to make ATP
4. Net ATP = (2 used and 4 produced) 2 ATP per glucose
Link reaction and Krebs cycle
1. Link Reaction
  1. Takes place in matrix of mitochondria
  2. CO2 removed from pyruvate, converting it to a 2C compound
    1. Hydrogen removed by NAD, forming NADH
    2. Immediately combines with coenzyme A to form acetyl coenzyme A
2. Krebs Cycle
  1. ACA combines with 4C compound to form a 6C compound
    1. Gradually converted back to 4C compound by a series of reactions
      1. CO2 removed, more hydrogen picked up by NAD (form NADH) and FAD (form FADH)
  2. Takes place in mitochondria matrix
Oxidative phosphorylation
1. Electron transport chain = Hydrogens from NADH and FADH split into protons and electrons, allowing the electrons to pass along a chain of molecules
  1. Electrons lose energy as they move along, which is used to actively transport hydrogen ions from the matrix to the inner membrane space
    1. Creates a high conc. of H+ ions
    2. Hydrogen ions then diffuse back into matrix, passing through ATP synthase enzymes
      1. Movement of ions provides enough energy to cause ADP and inorganic phosphate to bind, forming ATP
  2. At end of chain, electrons and protons rejoin, combining with oxygen to from water
2. Chemiosmosis = active transport and subsequent reactions
Anaerobic respiration
1. No oxygen = no oxidative phosphorylation = no reoxidised NAD = no NAD or FAD in Krebs cycle = process comes to a halt
  1. Glycolysis not affected = if pyruvate is still produced at the end, it can be removed and used to convert NADH back to NAD
2. Lactate Pathway
  1. NAD regenerated by converting pyruvate into lactate
    1. Lactate travels in blood plasma to liver, where it is converted back to pyruvate
      1. Requires oxygen, so more is needed after exercise = oxygen debt
      2. Pyruvate is either oxidised, or converted to glucose
  2. Animals
3. Ethanol Pathway
  1. Plants and yeast
  2. Pyruvate converted to ethanol
4. ATP yield
  1. Anaerobic respiration = small amounts of ATP per glucose, as only glycolysis is completed
  2. Aerobic respiration = between 30 and 32 ATP per glucose,
    1. 4 produced directly and 28 from oxidative phosphorylation
Photosynthetic pigments
1. Photosynthesis = Light energy splits water molecules to release hydrogen, producing ATP and reducing NADP to NADPH
  1. ATP and NADPH used to add hydrogen to CO2, producing glucose
  2. Oxygen from water released as a waste product
2. Chloroplast pigments
  1. Pigment = substance that absorbs light of specific wavelengths, creating different colours by reflecting the other colours
  2. Chlorophyll = main pigment in chloroplasts
    1. Green, as it reflects green light
    2. Chlorophyll A = most abundant pigment
    3. Chlorophyll B = similar to CA, but not as abundant
  3. Carotenoids and Xanthophylls = other pigments, absorb light that chlorophyll cannot, pass energy onto chlorophyll
3. Absorption spectra = shows wavelengths absorbed by different pigments
Photosynthesis
1. Chloroplasts
  1. Organelles surrounded by 2 membranes, found in mesophyll and guard cells
    1. Membrane called lamellae, where LDR take place
      1. Contain chlorophylls, arranged in photosystems
        2 types of photosystem, PSI and PSII
      2. Thylakoids = fluid-filled sacs between membranes
        Involved in photophosphorylation
        Arranged in stacks called grana
    2. Stroma = inside material, site of LIR
2. Light-Dependent Stage
  1. PSI and PSII absorb light energy, exciting electrons so that they leave the chlorophyll
    1. PSII photolyses water, splitting it and causing the hydrogen to lose an electron, becoming H+
      1. Electrons taken up by PSII chlorophyll, to replace those lost
      2. Oxygen atoms combine and leave plant
      3. Electrons from PSII picked up by carriers in the thylakoids
        Move along in similar fashion to ETC in OP
        Energy lost used to convert ADP into ATP through PP
        At end of the chain, electrons are picked up by PSI, replacing electrons lost
      4. Electrons from PSII passed down a NADP chain
        NAPD also collects H+ from water, becoming NADPH
  2. NADPH and ATP both used in LIR
3. Light-Independent Stage
  1. Stroma = the enzyme ribulose biophosphate carboxylase (RUBISCO) is found
    1. CO2 enters stroma, using the active site of RUBISCO to bind with ribulose bisphosphate (RuBP), a 5C compound, which froms GP
      1. Carbon fixation
      2. ATP and hydrogen used to convert GP into triose phosphate (GALP)
        Most GALP used to make RuBP for more carbon fixation, while the rest is used to make glucose
  2. Calvin Cycle = a cyclical series of reactions
4. Limiting factors
  1. Light intensity = affects rate of LDR
  2. Temperature = affects rate of LIR
    1. High temp = more kinetic energy = more collisions
  3. Carbon dioxide conc. in atm = necessary reactant
  4. If any of the conditions get too low, photosynthesis rate will reduce, but the factor with the greatest effect is the 'limiting factor'

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	Created by amy smith over 6 years ago