photosynthesis
DESCRIPTION
Photosynthesis. Photosynthesis with Hank!. Life from Light and Air. Obtaining the materials. sunlight leaves = solar collectors CO 2 stomates = gas exchange H 2 O uptake from roots nutrients N, P, K, S, Mg, Fe… uptake from roots. Concurrent Reactions. - PowerPoint PPT PresentationTRANSCRIPT
Photosynthesis
Life from Light and Air
Phot
osyn
thes
is w
ith
Ha
nk!
Obtaining the materials– sunlight• leaves = solar collectors
– CO2• stomates = gas
exchange– H2O• uptake from roots
– nutrients• N, P, K, S, Mg, Fe… • uptake from roots
Concurrent Reactions
Light-Dependent Reactions*Key to these rxns is light absorption
Success lies in photosystems – 2 part complex
1. Antenna complex – site of absorption; excites electrons & passes them on
2. Reaction center – redox-rxns occur here; excited ele- transferred to electron acceptor
reactioncenter
antennapigments
PS
680
H+ + ½ O2 +
PS
700
NADP + + 2H +
NADPH
ADP + P
ATP!
- pheophytin- plastoquinone
- Cytochro
mecomplex
- H + ion
- ferredoxin- ele -
- NADP+ Reductase
- ATP Syntha
se
To Calvin Cycle!!!
Stroma
Lumen
Step 1: Light absorbed in PS II excites ele- (from H2O splitting) → passed to electron acceptor (pheophytin)Step 2: Plastoquinone(PQ) shuttles high energy ele- through series of redox rxns (ETC 1); passes through cytochrome complex, driving in H+, ↑ [H+] = ↓ pHStep 3: De-energized ele- are passed off to plastocyanin (PC) → PS I re-excites ele- and ferredoxin shuttles through ETC 2
Step 4: a) Ele- reduce NADP+ to NADPH at NADP+ reductase
b) H+ pumped out via ATP Synthase – activateschemiosmosis → production of ATP from ADP
Regulation of the Light Reaction
– Calvin cycle uses more ATP than NADPH
– If there is enough, NADPH production is turned off
18 ATP +12 NADPH
1 C6H12O6
ATP
Light-INdependent Reactions
•Want to make C6H12O6 → synthesis**How? From what? What raw materials are available?
CO2
C6H12O6
NADPH
NADPreduces CO2
carbon fixation
NADP
From CO2 C6H12O6
• CO2 has very little chemical energy– fully oxidized
• C6H12O6 has a LOT of chemical energy– highly reduced
• Synthesis = endergonic process– put in a lot of energy
• Reduction of CO2 C6H12O6 proceeds in many small uphill steps– each catalyzed by specific enzyme– uses energy stored in ATP & NADPH
←from light rxns!
starch,sucrose,cellulose& more
1C CO2
Calvin cycle
5CRuBP
3C
RuBisCo
1. Carbon fixation
2. Reduction
3. Regenerationof RuBP
ribulose bisphosphateribulose
bisphosphate
carboxylase
6 NADP6 NADPH 6 ADP
6 ATP
3 ADP3 ATP
usedto makeglucose
3C
3CG3P aka PGAL
glyceraldehyde-3-P
C C C C C
C C C C C
C C C C C
6CC C C C C C
C C C C C CC C C C C C
C C C
C C CC C CC C CC C CC C C
PGAphosphoglycerate
C C C
C C CC C CC C CC C CC C CC C C
CC
C
C C C= =
|H
|H
|H
|H
|H
|HC C C– –
5C
To G3P and Beyond!• Resulting 3-C Sugar
- important intermediate• G3P glucose carbohydrates
lipids phospholipids, fats, waxes amino acids proteins nucleic acids DNA, RNA
To G3Pand beyond!
A little more about RuBisCo…
•Enzyme which fixes carbon from air•ribulose bisphosphate carboxylase
• the most important enzyme in the world!
**It makes life out of air!**
• most abundant enzyme
“Banking”• Keeping the books straight…
– 6 turns of Calvin cycle = 1 C6H12O6 (6C)– 6 CO2 1 C6H12O6 (6C)– 18 ATP + 12 NADPH 1 C6H12O6
– Left over ATP from light reactions used elsewhere by cell
Sum it Up: Light Reactions
O2
H2O
Energy BuildingReactions
ATP
produces ATP & NADPH
releases O2 as waste
sunlight
H2O ATP O2lightenergy ++ + NADPH
NADPH
Calvin Cycle
sugars
CO2
SugarBuildingReactions
ADP
builds sugars
uses ATP & NADPH
recycles ADP & NADP+ ATP
NADPH
NADP
CO2 C6H12O6 ++ + NADPATP + NADPH ADP
Supporting a biosphere
• Big Picture: photosynthesis is THE most important process for continuation of life on Earth• Each year photosynthesis…• captures 121 billion tons of CO2
• synthesizes 160 billion tons of carbohydrates
• heterotrophs depend on plants for food, fuel, & raw materials
Light Depedent Review:
• Where did the energy come from?• Where did the electrons come from?
• Where did the H2O come from?• Where did the O2 come from?
• Where did the O2 go? • Where did the H+ come from?• Where did the ATP come from?• What will the ATP be used for?
• Where did the NADPH come from?• What will the NADPH be used for?
Light Independent Review II:
• Where did the CO2 come from?• Where did the CO2 go?
• Where did the H2O come from?• Where did the H2O go?
• Where did the energy come from?• What’s the energy used for?
• What will the C6H12O6 be used for?• Where did the O2 come from?
• Where will the O2 go?• What else is involved…not listed in this
equation?
6CO2 6H2O C6H12O6lightenergy + ++ 6O2
Adaptations in Alternative Environments C4 Path• CO2 stored is mesophyll & released in vascular tissue
Adaptations in Alternative EnvironmentsCAM Path• Stomata open at night – CO2 stored in vacuoles for later use
Combating Photorespiration
Photorespiration – rxn between RuBP & O2 when [O2] is high → uses ATP & produces CO2
Favored ONLY when [O2]
exceeds [CO2]
C4 Path CAM Plants
Store CO2