TOPIC 5

TOPIC 5

1. Aerobic respiration

   • ATP
     • Energy currency of living cells, as lots of energy is released when hydrolysed
     • Made by respiration, which is a series of enzyme controlled reactions in which energy is released from organic substances and transferred to ATP
   • Stages of respiration
     • Glycolysis: glucose to pyruvate
     • Link reaction: pyruvate to acetyl coenzyme A
     • Krebs cycle: ACeA enter cyclical reactions
     • Oxidative phosporylation: ADP converted to ATP

2. Glycolysis

   • Takes place in cytoplasm
   • Glucose phosphorylated to produce hexose biphosphate, which splits into 2 molecules of glycerate 3-phospate (GP)
     • Removal of hydrogens = taken by NAD, producing NADH
   • Each GP is converted to pyruvate
     • Removed phosphate groups added to ADP to make ATP
   • Net ATP = (2 used and 4 produced) 2 ATP per glucose

3. Link reaction and Krebs cycle

   • Link Reaction
     • Takes place in matrix of mitochondria
     • CO2 removed from pyruvate, converting it to a 2C compound
       • Hydrogen removed by NAD, forming NADH
       • Immediately combines with coenzyme A to form acetyl coenzyme A
   • Krebs Cycle
     • ACA combines with 4C compound to form a 6C compound
       • Gradually converted back to 4C compound by a series of reactions
         • CO2 removed, more hydrogen picked up by NAD (form NADH) and FAD (form FADH)
     • Takes place in mitochondria matrix

4. Oxidative phosphorylation

   • Electron transport chain = Hydrogens from NADH and FADH split into protons and electrons, allowing the electrons to pass along a chain of molecules
     • Electrons lose energy as they move along, which is used to actively transport hydrogen ions from the matrix to the inner membrane space
       • Creates a high conc. of H+ ions
       • Hydrogen ions then diffuse back into matrix, passing through ATP synthase enzymes
         • Movement of ions provides enough energy to cause ADP and inorganic phosphate to bind, forming ATP
     • At end of chain, electrons and protons rejoin, combining with oxygen to from water
   • Chemiosmosis = active transport and subsequent reactions

5. Anaerobic respiration

   • No oxygen = no oxidative phosphorylation = no reoxidised NAD = no NAD or FAD in Krebs cycle = process comes to a halt
     • Glycolysis not affected = if pyruvate is still produced at the end, it can be removed and used to convert NADH back to NAD
   • Lactate Pathway
     • NAD regenerated by converting pyruvate into lactate
       • Lactate travels in blood plasma to liver, where it is converted back to pyruvate
         • Requires oxygen, so more is needed after exercise = oxygen debt
         • Pyruvate is either oxidised, or converted to glucose
     • Animals
   • Ethanol Pathway
     • Plants and yeast
     • Pyruvate converted to ethanol
   • ATP yield
     • Anaerobic respiration = small amounts of ATP per glucose, as only glycolysis is completed
     • Aerobic respiration = between 30 and 32 ATP per glucose,
       • 4 produced directly and 28 from oxidative phosphorylation

6. Photosynthetic pigments

   • Photosynthesis = Light energy splits water molecules to release hydrogen, producing ATP and reducing NADP to NADPH
     • ATP and NADPH used to add hydrogen to CO2, producing glucose
     • Oxygen from water released as a waste product
   • Chloroplast pigments
     • Pigment = substance that absorbs light of specific wavelengths, creating different colours by reflecting the other colours
     • Chlorophyll = main pigment in chloroplasts
       • Green, as it reflects green light
       • Chlorophyll A = most abundant pigment
       • Chlorophyll B = similar to CA, but not as abundant
     • Carotenoids and Xanthophylls = other pigments, absorb light that chlorophyll cannot, pass energy onto chlorophyll
   • Absorption spectra = shows wavelengths absorbed by different pigments

7. Photosynthesis

   • Chloroplasts
     • Organelles surrounded by 2 membranes, found in mesophyll and guard cells
       • Membrane called lamellae, where LDR take place
         • Contain chlorophylls, arranged in photosystems
           • 2 types of photosystem, PSI and PSII
         • Thylakoids = fluid-filled sacs between membranes
           • Involved in photophosphorylation
           • Arranged in stacks called grana
       • Stroma = inside material, site of LIR
   • Light-Dependent Stage
     • PSI and PSII absorb light energy, exciting electrons so that they leave the chlorophyll
       • PSII photolyses water, splitting it and causing the hydrogen to lose an electron, becoming H+
         • Electrons taken up by PSII chlorophyll, to replace those lost
         • Oxygen atoms combine and leave plant
         • 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
         • Electrons from PSII passed down a NADP chain
           • NAPD also collects H+ from water, becoming NADPH
     • NADPH and ATP both used in LIR
   • Light-Independent Stage
     • Stroma = the enzyme ribulose biophosphate carboxylase (RUBISCO) is found
       • CO2 enters stroma, using the active site of RUBISCO to bind with ribulose bisphosphate (RuBP), a 5C compound, which froms GP
         • Carbon fixation
         • 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
     • Calvin Cycle = a cyclical series of reactions
   • Limiting factors
     • Light intensity = affects rate of LDR
     • Temperature = affects rate of LIR
       • High temp = more kinetic energy = more collisions
     • Carbon dioxide conc. in atm = necessary reactant
     • If any of the conditions get too low, photosynthesis rate will reduce, but the factor with the greatest effect is the 'limiting factor'