biology unit 3

• ATP


  The major energy currency of the cell, used for all reactions in all cells
• ATP synthesis

  1. Protons pass through ATP synthetase

  2. Electrochemical gradient provides potential energy

  3. Phosphorylation of ADP to form ATP
• Chemiosmosis is the flow of protons down an electrochemical gradient, through ATP synthetase, which provides the potential energy necessary to synthesise ATP by phosphorylation
• Electron transport chain and proton gradients

  1. High energy electrons pass from carrier to carrier

  2. Proton pumps transport protons into intermembrane/thylakoid space

  3. Protons flow through ATP synthetase to generate ATP
• Photosynthetic pigments


  • Absorb light energy at particular wavelengths
  • Examples: chlorophyll a and b, carotene, xanthophylls
• Chromatography and Rf values

  Used to separate and identify photosynthetic pigments
• Absorption spectrum


  Shows how much light is absorbed by a pigment at different wavelengths
• Action spectrum


  Shows the rate of photosynthesis at different wavelengths of light
• Englemann's experiment with spirogyra showed that the blue and red regions of the spectrum caused the most photosynthetic activity
• Antenna complexes

  • Contain photosynthetic pigments that absorb light energy and pass it to the reaction centre
• Photosystem I (PSI)

  Absorption peak of 700nm
• Photosystem II (PSII)

  Absorption peak of 680nm
• Cyclic photophosphorylation

  1. High energy electrons pass from PSI to electron acceptor

  2. Electrons returned to PSI

  3. Generates proton gradient for ATP synthesis
• Non-cyclic photophosphorylation

  1. High energy electrons from PSI passed to NADP

  2. PSI steals electron from PSII

  3. PSII passes electron to electron transport system
• Photolysis

  Splitting of water by light, producing protons, electrons and oxygen
• The products of the light dependent stage are ATP and reduced NADP, which are essential for the light independent stage or Calvin cycle
• Non-cyclic photophosphorylation can be illustrated as a Z scheme
• Photosystems


  I and II
• Electron transport system


  Generates the proton gradient necessary for photophosphorylation and ATP synthesis
• NADPH2


  Reduced NADP
• Photolysis


  Splitting of water by light, producing protons (hydrogen ions), electrons and oxygen
• The water molecules used for photolysis are found in the thylakoid space
• ATP (energy source) and reduced NADP (reducing power) are needed to drive the Calvin cycle or light independent stage
• Without ATP and reduced NADP, the Calvin cycle will stop and carbon dioxide will not be fixed into carbohydrate
• The plant will die as there will be no glucose for respiration
• RUBP


  5C ribulose bisphosphate
• Calvin cycle


  Fixes carbon dioxide into carbohydrate
• GP


  3C glycerate-3-phosphate
• TP


  3C triose phosphate
• TP is converted into glucose and then starch
• Most of the TP is converted into RUBP (using energy from ATP) to regenerate RUBP and allow the light independent stage to continue
• Lipids, proteins and carbohydrates can be made from the products of the Calvin cycle
• Interpreting autoradiographs


  Alga chlorella was exposed to 14CO2, samples taken at 5 second intervals and radioactive compounds separated by chromatography
• After 5 seconds, only the early products of the Calvin cycle are observed as they are produced first
• After 30 seconds, more GP and TP have formed, and other molecules like amino acids and sucrose have also formed
• Subsequent samples would contain more complex, larger molecules such as starch, lipids and proteins
• Limiting factors


  Factors that become too low and decrease the rate of photosynthesis
• As light intensity increases


  The rate of photosynthesis increases until it reaches saturation point
• Beyond saturation point


  The rate of photosynthesis plateaus (levels off)
• At high CO2 concentrations


  Light intensity is limiting the rate of photosynthesis, not temperature