Photosynthesis

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Photosynthesis

• 1. Occurs in chloroplasts in eukaryotes,
  cytoplasm of prokaryotes
• 2. Photosynthetic pigments- chlorophyll a, b, c
  
• 3. Other pigments- carotenoids xanthophyll

2
Chloroplast Structure

• 1. Located in mesophyll cells of plants
• 2. Size- 5-10mm

3
Light Reactions

• 1. Light dependent rxns
• 2. In the thylakoid membranes of the grana in the
  chloroplast

4
Dark Reactions

• 1. Light independent rxns
• 2. In the stroma in the chloroplast

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Cyclic Electron Path, CEP

• 1. ATP production only
• 2. Some photosynthetic bacteria only have CEP

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ATP Production, CEP

• 1. Light strikes photosystem I (PS I) chlorophyll
  a
• 2. Energized electrons (e- ) leave PS I
  chlorophyll a enter e- acceptor cytochrome
  system
• 3. e- pass down cytochrome releasing energy
• 4. Energy used to phosphorylate ADP to ATP, ATP
  synthase

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Noncyclic Electron Path, NEP

• 1. Light rxns or light dependent
• 2. ATP production, water split, NADPH production

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ATP Production, NEP

• 1. Light strikes photosystem II (PS II)
  chlorophyll a

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ATP Production, NEP

• 2. Energized electrons (e- ) leave PS II
  chlorophyll a enter e- acceptor cytochrome
  system

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ATP Production, NEP

• 3. e- pass down cytochrome releasing energy

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ATP Production, NEP

• 4. Energy used to phosphorylate ADP to ATP, ATP
  synthase

12
ATP Production, NEP

• 1. Light strikes photosystem II (PS II)
  chlorophyll a
• 2. Energized electrons (e- ) leave PS II
  chlorophyll a enter e- acceptor cytochrome
  system
• 3. e- pass down cytochrome releasing energy
• 4. Energy used to phosphorylate ADP to ATP, ATP
  synthase

13
Water Split, NEP

• 1. e- leave PS II chlorophyll a

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Water Split, NEP

• 2. e- from water replace leaving e-

15
Water Split, NEP

• 3. Loss of e- splits water to hydrogen ions and
  oxygen
• 2H20 g 4H O2 4e-

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Water Split, NEP

• e- leave PS II chlorophyll a
• 2. e- from water replace leaving e-
• 3. Loss of e- splits water to hydrogen ions and
  oxygen
• 2H20 g 4H O2 4e-

17
NADPH Production, NEP

• 1. Light strikes PS I chlorophyll a

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NADPH Production, NEP

• 2. e- leave PS I chlorophyll a enter e-
  acceptor cytochrome system

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NADPH Production, NEP

• 3. Low energy e- from PS II ATP production
  replace leaving e-

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NADPH Production, NEP

• 4. e- pass down cytochrome system changing NADP
  to NADP-

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NADPH Production, NEP

• 5. NADP- H from PS II form NADPH

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NADPH Production, NEP

• 1. Light strikes PS I chlorophyll a
• 2. e- leave PS I chlorophyll a enter e-
  acceptor cytochrome system
• 3. Low energy e- from PS II ATP production
  replace leaving e-
• 4. e- pass down cytochrome system changing NADP
  to NADP-
• 5. NADP- H from PS II form NADPH

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Carbohydrate Synthesis

• 1. Dark rxn, light independent rxn, or Calvin
  cycle
• 2. CO2 fixation, CO2 reduction, Ribulose bis
  phosphate regeneration

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CO2 Fixation

• 1. CO2 combines with ribulose bis phosphate
  (RubP)
• 2. Forms unstable 6 C molecule
• 3. RubP carboxylase mediates rxn

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CO2 Reduction

• 1. Unstable 6 C molecule instantly forms two
  3-phosphoglycerate (PGA) molecules
• 2. PGA reduced to glyceraldehyde-3-phosphate
  (PGAL)
• 3. Uses energy from ATP and H from NADPH
• 4. PGAL converted to glucose or other organic
  molecules

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RubP Regeneration

• 1. Five of six PGAL used to form three RubP
• 2. Net gain from three CO2 is one PGAL

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CO2 Fixation Paths

• C3 plants- wheat, rice, oats
• 2. C4 plants- sugarcane, corn
• 3. CAM plants- cacti, most succulents

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C3 Path

• CO2 fixation results in 3 C molecule, PGA . . .
• 2. Chloroplasts in mesophyll cells
• 3. Mesophyll cells in roughly parallel layers
  around bundle cells
• 4. Mostly temperate regions

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C4 Path

• CO2 fixation results in 4 C molecule,
  oxaloacetate, occurs in mesophyll cell
  chloroplasts
• 2. Oxaloacetate enters bundle cell chloroplasts
  releases CO2 to Dark rxn
• 3. Mesophyll cells concentrically arranged around
  bundle cells
• 4. Mostly tropical regions

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CAM Path

• Crassulacean acid metabolism, occurs at night,
  CO2 fixation results in 4 C molecule
• 2. 4 C molecule stored in mesophyll cell vacuole
  until next day
• 3. CO2 released Dark rxn proceed
• 4. Mostly arid regions

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