Topic 5

• Location of light dependent reaction: Thylakoid membranes of chloroplast
• Location of light independent reaction: Stroma of chloroplast
• Chloroplast structure:

  A) Inner membrane

  B) Stroma

  C) Lumen

  D) Lamella

  E) Thykaloid

  F) Granum

  G) Outer membrane

  H) Intermembrane space

  
• Thylakoid membranes:

  • Folded membranes containing photosynthetic proteins (chlorophyll)
  • embedded with transmembrane electron carrier proteins
  • involved in the LDRs
• Chlorophyll:

  • Located in proteins on thylakoid membranes
  • mix of coloured proteins that absorb light
  • different proportions of each pigment lead to different colours on leaves
• Light-dependent reaction (LDR):

  • First stage of photosynthesis
  • occurs in thylakoid membranes
  • uses light energy and water to create ATP and reduced NADP for LIR
  • involves photoionisation of chlorophyll, photolysis and chemiosmosis
• Photolysis: Light energy absorbed by chlorophyll splits water into oxygen, H+ and e- .
• Photolysis formula:

  H20 --> 1/2 02 + 2e- + 2H+
• Products of photolysis:

  • H+ is Picked up by NADP to form reduced NADP for LIR
  • e- is passed along chain of electron carrier proteins
  • oxygen is used in respiration or diffuses out leaf via stomata
• Photoionisation of chlorophyll:

  • Light energy absorbed by chlorophyll excites electrons so they move to a higher energy level and leave chlorophyll
  • some of the energy released is used to make ATP and reduced NADP
• Chemiosmosis:

  • Electrons that gained energy move along a series of electron carriers in thylakoid membrane
  • release energy as they go along which pumps proteins across thylakoid membrane
  • electrochemical gradient made
  • protons pass back across via ATP synthase enzyme producing ATP down their conc. gradient
• What happens to protons after chemiosmosis?

  • Combine with co-enzyme NADP to become reduced NADP
  • reduced NADP used in LIR
• Products of LDR:

  • ATP (used in LIR)
  • reduced NADP (used in LIR)
  • oxygen (used in respiration / diffuses out stomata)
• Light independent reaction (LIR):

  • Calvin cycle
  • uses CO2, reduced NADP and ATP to form hexose sugar
  • occurs in stroma which contains the enzyme Rubisco
  • temperature-sensitive
• Calvin Cylce:

  A) GP

  B) RUBP

  C) TP

  
• RuBP:

  • Ribulose Bisphosphate
  • 5-carbon molecule
• GP:

  • Glycerate-3-phosphate
  • 3-carbon molecule
• TP:

  • Triose phosphate
  • 3-carbon molecule
• Producing hexose sugar in LIR:

  • Takes 6 cycles
  • glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose)
  • can be converted to glycerol to combine with fatty acids to make lipids
• Limiting factor: A factor which, if increased, the rate of the overall reaction also increases
• How light intensity limits photosynthesis:

  • If reduced, levels of ATP and reduced NADP would fall
  • LDR limited - less photolysis and photoionisation
  • GP cannot be reduced to TP in LIR

  
• How temperature limits photosynthesis:

  • LIR inhibited - enzyme controlled (Rubisco)
  • up to optimum, more collisions and E-S complexes
  • above optimum, H-bonds in tertiary structure break, active site changes shape - denatured

  
• How CO2 concentration limits photosynthesis:

  • If reduced, LIR inhibited
  • less CO2 to combine with RuBP to form GP
  • less GP reduced to TP
  • less TP converted to hexose and RuBP regenerated
• Agricultural practices to maximise plant growth:

  • Growing plants under artificial lighting to maximise light intensity
  • heating in greenhouse to increase temperature
  • burning fuel to release CO2
• Benefit of agricultural practices for plant growth:

  • Faster production of glucose -> faster respiration
  • more ATP to provide energy for growth e.g. cell division + protein synthesis
  • higher yields so more profit
• Products of LIR:

  • Hexose sugar
  • NADP - used in LDR
• Stages of aerobic respiration:

  1. Glycolysis
  2. Link reaction
  3. Krebs cycle
  4. Oxidative phosphorylation
• Location of glycolysis: Cytoplasm
• Coenzymes:

  • A molecule which aids / assists an enzyme
  • NAD and FAD in respiration both gain hydrogen to form reduced NAD (NADH) and reduced FAD (FADH)
  • NADP in photosynthesis gains hydrogen to form reduced NADP (NADPH)
• Products of glycolysis:

  • Net gain of 2 ATP
  • 2 reduced NAD
  • 2 pyruvate molecules
• How many ATP molecules does glycolysis produce?

  • 2 ATP molecules used to phosphorylate glycose to glucose phosphate
  • 4 molecules generated in oxidation of TP to pyruvate
  • net gain 2 ATP molecules
• Location of the link reaction: Mitochondrial matrix
• Products of the link reaction per glucose molecule:

  • 2 acetylcoenzyme A molecules
  • 2 carbon dioxide molecules released
  • 2 reduced NAD molecules
• Location of the Krebs cycle: Mitochondrial matrix
• Krebs cycle:

  • Acetylcoenzyme A combines with 4C molecule to produce a 6C molecule - enters cycle
  • oxidation-reduction reactions

  
• Products of the Krebs cycle per glucose:

  • 8 reduced coenzymes
  • 6 reduced NAD
  • 2 reduced FAD
  • 2 ATP
  • 4 carbon dioxide
• Location of oxidative phosphorylation: Cristae of mitochondria
• Mitochondria structure:

  • Double membrane with inner membrane folded into cristae
  • enzymes in matrix

  
• Role of electrons in oxidative phosphorylation:

  • Electrons pass down series of electron carrier proteins, losing energy as they move
  • energy released actively transports H+ from mitochondrial matrix to intermembranal space
  • electrochemical gradient generated
• How is ATP made in oxidative

  phosphorylation:

  • Protons move down electrochemical gradient back into matrix via ATP synthase
  • ATP created
  • movement of H+ is chemiosmosis