Lecture 3 Outline (Ch. 8)I. Photosynthesis overview
A. Purpose B. Location
II. The light vs. the “dark” reaction
III. Chloroplasts pigments A. Light absorption B. Types
IV. Light reactions A. Photosystems B. Photophosphorylation
V. The light independent reaction (“dark” reaction) A. Carbon “fixation” B. Reduction C. Regeneration
VI. Alternative plants
Photosynthesis - overview
Overall purpose:
Photosynthesis - overview
• photosynthesis –
light chemical energy
• complements respiration
Energy for all life on earth ultimately comes from photosynthesis
Cellular Respiration:(Exergonic)
Photosynthesis:(Endergonic)
Cellular Respiration vs. Photosynthesis
Photosynthesis – chloroplast recap
Outer membrane
Inner membrane
Thylakoid membrane
Stroma
Thylakoid space
Intermembrane space
Photosynthesis - overview
• Photosynthesis -
1. light rxn: store energy & split water – “photo”
2. dark rxn: “fix” CO2 & make sugars – “synthesis”
Calvin cycle
NADPH & ATP
Redox Reactions
Equation for photosynthesis
6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O
Photosynthesis - overview
– thylakoid membrane
– thylakoid space– stroma
• light reactions: • dark reactions:
Light
H2O
Chloroplast
LightReactions
NADP+
PADP+
ATP
NADPH
O2
CalvinCycle
CO2
[CH2O]
(sugar)
Photosynthesis – light absorption
• visible light ~380 to 750 nm
• chloroplast pigments – abs blue-violet & red
- transmit and reflect green
• pigments:
• chlorophyll a
• accessory pigments
-energy-absorbing ring
-hydrocarbon tail
- carotenoids
- photoprotective
Photosynthesis – light absorption
- chlorophyll b
• 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
Photosynthesis – light absorption
• chlorophyll abs light
Photosynthesis – light absorption
• e- excited
• more energy
• energy transferred
Pigments have two states: ground & excited
Photosynthesis – light absorption
light harvesting complex
• energy absorbed from light - to pigments
• to reaction center
- two special chlorophyll a
- 1° electron acceptor
• light harvesting complex & reaction center = photosystem (PS)
- proteins
Pigments are held by proteins in the thylakoid membranes
Photosynthesis – energy transfer
• Photosystem I (PS I) & PS II
• Difference – light wavelength, proteins, where e- from
Light
Thylakoidmembrane
THYLAKOID SPACE
STROMA
Photosystem II Photosystem I
Light
Photosynthesis – energy transfer
• PSII: absorbs 680 nm,
• PS I: absorbs 700 nm,
(less energy)
splits water, powerful ETC, ATP made
e- from PSII, short ETC, NADPH made
Photosynthesis – energy transfer
• e- from PS II electron transport chain (ETC) PS I
NADPH• e- from PS I 2nd ETC e- carrier: NADP+
• e- in PS II, from split H20
Photosynthesis – chemiosmosis
• How is ATP produced?
Chemiosmosis
photophosphorylation
• e- down ETC, H+ to thylakoid space
• H+ conc. gradient
• H+ down gradient, ATP synthase
Light reaction - summary
• inputs: light energy, H2O
• PS II, ETC, PS I, ETC
• outputs:
ATP
NADPH
O2 (waste)
Self-Check
Step of Photosynthesis
Location IN chloroplast
Inputs Outputs ATP produced?
(don’t need #)
e- carriers loaded?
Light reaction overall
PSII
PSI
“Dark” reaction overall
Know figures of chloroplast reactions/locations!
Photosynthesis – energy transfer
“Dark” reaction (Light-independent Reaction)
6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O
• “Dark” reaction: Calvin cycle
• regenerative
• anabolic
• CO2 in, sugar out
• during daylight
CO2
NADP+
ADPPi+
RuBP 3-PhosphoglycerateCalvinCycle
G3PATP
NADPH Starch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
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)
Reduction
• #2 – reduction
• reduced 3-C: G3P
• 3-C reduced
• e- from NADPH
• 3 stages of Calvin-cycle:
Regeneration of C-acceptor
• multiple steps
• uses ATP
• every 3 cycles:
1 G3P made
3 RuBP regenerated
• #3 – regenerate C-acceptor
• still 5 G3P 3 RuBP
• C3 plants – CO2 fixed into 3-C
• 3 stages of Calvin-cycle:
Self-Check
Step of Photosynthesis
Location IN chloroplast
Inputs Outputs ATP produced
(don’t need #)
e- carriers loaded
Light reaction overall
PSII
PSI
“Dark” reaction overall
Alternate methods of C fixation
Alternate methods of C fixation
CO2
NADP+
ADPPi+
RuBP 3-PhosphoglycerateCalvinCycle
G3PATP
NADPH Starch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
• CO2 in stomata
• open, lose water
• O2 fixed – photorespiration – inefficient
• hot, dry – open stomata less; lowers water loss, lowers CO2
• fix CO2 into 4-C molecules
Photosynthesis – summary
• light reaction: Light energy + H2O
• light-independent:
CO2, NADPH, ATP
O2, NADPH, ATP
Thylakoids
G3P (sugar), RuBP
Stroma
Photosynthesis – summary
Where do photosynthetic products go?
Photosynthesis – in context of big picture
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