Photosynthesis

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Photosynthesis
By
Muhammad Iqbal Khan
SS
Biology Email ID
mikhan1313_at_yahoo.com
Contact 0923135448175
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Lecture 3 Outline (Ch. 8)

• Photosynthesis overview
• A. Purpose
• B. Location
• The light vs. the dark reaction
• Chloroplasts pigments
• A. Light absorption
• B. Types
• Light reactions
• A. Photosystems
• B. Photophosphorylation
• V. The light independent reaction (dark
  reaction)
• A. Carbon fixation
• B. Reduction
• C. Regeneration
• VI. Alternative plants

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Photosynthesis - overview
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Photosynthesis - overview
Overall purpose
photosynthesis light ?chemical energy
complements respiration
Energy for all life on earth ultimately comes
from photosynthesis
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Cellular Respiration vs. Photosynthesis
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Photosynthesis chloroplast recap
Outer membrane Inner membrane Thylakoid membrane
Stroma Thylakoid space Intermembrane space
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Photosynthesis - overview
Photosynthesis -
1. light rxn store energy split water photo
NADPH ATP
2. dark rxn fix CO2 make sugars synthesis
Calvin cycle
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Redox Reactions
Equation for photosynthesis
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Photosynthesis - overview
light reactions
dark reactions
thylakoid membrane
stroma
thylakoid space
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Photosynthesis light absorption
visible light 380 to 750 nm
chloroplast pigments abs blue-violet red
- transmit and reflect green
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Photosynthesis light absorption
pigments
chlorophyll a
-energy-absorbing ring
-hydrocarbon tail
accessory pigments
- chlorophyll b
- carotenoids
- photoprotective
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Photosynthesis light absorption
chlorophyll a abs blue-violet, red 400-450,
650-700 nm
chlorophyll b carotenoids abs broadly
blue-violet mid-400s
more wavelengths used for photosynthesis more
light energy absorbed
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Photosynthesis light absorption
Pigments have two states ground excited
chlorophyll abs light
e- excited
more energy
energy transferred
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Photosynthesis light absorption
Pigments are held by proteins in the thylakoid
membranes
light harvesting complex
energy absorbed from light - to pigments
to reaction center
- two special chlorophyll a
- proteins
- 1 electron acceptor
light harvesting complex reaction center
photosystem (PS)
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Photosynthesis energy transfer
Photosystem I (PS I) PS II
Difference light wavelength, proteins, ?
where e- from
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Photosynthesis energy transfer
PSII absorbs 680 nm,
splits water, powerful ETC, ATP made
PS I absorbs 700 nm, (less energy)
e- from PSII, short ETC, NADPH made
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Photosynthesis energy transfer
e- in PS II, from split H20
? NADPH
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Photosynthesis chemiosmosis
How is ATP produced?
Chemiosmosis
e- down ETC, H to thylakoid space
H conc. gradient
H down gradient, ATP synthase
photophosphorylation
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Light reaction - summary
inputs light energy, H2O
PS II, ETC, PS I, ETC
outputs ATP NADPH O2 (waste)
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Self-Check
Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced? (dont need ) e- carriers loaded?
Light reaction overall
PSII
PSI
Dark reaction overall
Know figures of chloroplast reactions/locations! ?
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Photosynthesis energy transfer
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Dark reaction (Light-independent Reaction)
Dark reaction Calvin cycle
regenerative
anabolic
CO2 in, sugar out
during daylight
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Carbon fixation
3 stages of Calvin-cycle
1 carbon fixation
CO2 link to 5-C
5-C ribulose bisphosphate (RuBP) - enzyme
Rubisco
abundant
6-C unstable split ? 2(3-C)
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Reduction
3 stages of Calvin-cycle
2 reduction
3-C reduced
e- from NADPH
reduced 3-C G3P
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Regeneration of C-acceptor
3 stages of Calvin-cycle
3 regenerate C-acceptor
still 5 G3P ? 3 RuBP
multiple steps
uses ATP
every 3 cycles 1 G3P made 3 RuBP regenerated
C3 plants CO2 fixed into 3-C
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Self-Check
Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced (dont need ) e- carriers loaded
Light reaction overall
PSII
PSI
Dark reaction overall
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Alternate methods of C fixation
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Alternate methods of C fixation
CO2 in ? stomata
open, lose water
hot, dry open stomata less lowers water
loss, lowers CO2
O2 fixed photorespiration inefficient
fix CO2 into 4-C molecules
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Photosynthesis summary
light reaction Light energy H2O
O2, NADPH, ATP
Thylakoids
light-independent CO2, NADPH, ATP
G3P (sugar), RuBP
Stroma
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Photosynthesis summary
Where do photosynthetic products go?
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Photosynthesis in context of big picture
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Lecture 3 Summary

• 1. Photosynthesis Overview (Ch. 8)
• Purpose
• Redox reactions
• Electron carriers sugars
• 2. Light (Ch. 8)
• Absorption pigments
• Light spectra/wavelengths
• 3. Locations of steps, inputs/outputs, purpose,
  description (Ch. 8)
• PSI vs. PS II
• Whole light reaction includes chemiosmosis
• dark reaction/Calvin cycle 3 steps
• 4. Alternate modes of photosynthesis (Ch. 8)
• 5. Photosynthesis context (Ch. 8)
• - Uses for products
• - Relationship of cell respiration
  and photosynthesis