Closed stomates
• Closed stomates lead to…– O2 builds up from light reactions
– CO2 is depleted in Calvin cycle• causes problems in Calvin Cycle
Inefficiency of Rubisco: CO2 vs O2
• Rubisco in Calvin cycle– carbon fixation enzyme
• normally bonds C to RuBP• building sugars
– when O2 concentration is high• Rubisco bonds O to RuBP
• O2 is alternative substrate
• breakdown sugars
photosynthesis
photorespiration
Rubisco = ribulose bisphosphate carboxylase / oxygenase
Oxygen Concentration
6Cunstable
intermediate
1C CO2
Calvin cycle review
5CRuBP
3CPGA
ADP
ATP
3CNADP
NADPH
ADP
ATP
G3Pto make glucose
Rubisco
3CG3PC3 plants
Calvin cycle with O2
5CRuBP
Rubisco
3C2C
lost as CO2 without
making ATP
photorespiration
O2
A good enzyme,gone BAD!
PGA
phosphoglycolate
Impact of Photorespiration:Oxidation of RuBP
loss of carbons CO2reduces production of photosynthesis
Reducing photorespiration • Separate carbon fixation from Calvin cycle
– C4 plants • physically separate carbon fixation from actual
Calvin cycle• different enzyme to capture CO2
– PEP carboxylase stores carbon in 4C compounds
• different leaf structure
– CAM plants• separate carbon fixation from actual Calvin cycle by
time of day• fix carbon (capture CO2) during night
– store carbon in organic acids
• perform Calvin cycle during day
C4 plants • A better way to capture CO2
– 1st step before Calvin cycle, fix carbon with enzymePEP carboxylase
• store as 4C compound
– adaptation to hot, dry climates
• have to close stomates a lot
– sugar cane, corn, other grasses…
PEP carboxylase O2
light reactions
• PEP carboxylase enzyme– higher affinity for CO2 than O2
(better than Rubisco)
– fixes CO2 in 4C compounds
– regenerates CO2 in inner cells for Rubisco phosphoenolpyruvate (3C) + CO2 oxaloacetate (4C)
C4 photosynthesis
CO2O2
CO2
O2
• Outer cells– light reaction & carbon
fixation– pumps CO2 to inner
cells – keeps O2 away from
inner cells• away from Rubisco
• Inner cells– Calvin cycle– glucose to veins
Physically separated C fixation from Calvin cycle
CAM (Crassulacean Acid Metabolism)
• Different adaptation to hot, dry climates– separate carbon fixation from Calvin cycle by time
– at night, open stomates & fix carbon in “storage” compounds• organic acids: malic acid, isocitric acid
– in day, close stomates & release CO2 from “storage” compounds to Calvin cycle• increases concentration of CO2 in cells
– succulents, some cacti, pineapple
It’s all inthe timing!
CAM plants
C4 vs CAM Summary
C4 plants separate 2 steps of C fixation anatomically in 2 different cells
CAM plants separate 2 steps of C fixation temporally at2 different times
solves CO2 / O2 gas exchange vs. H2O loss challenge
CR & Photo Review
Mrs. Confrey
Lab 4
• Conclusions– Pigments
• pigments move at different rates based on solubility in solvent
– Photosynthesis• light & unboiled
chloroplasts produced highest rate of photosynthesis
Lab 5: Cellular Respiration
• using respirometer to measure rate of O2 consumed
• Conclusions temp = respiration
Cellular Respiration
Cellular Respiration
Glycolysis summary endergonicinvest some ATP
exergonicharvest a little ATP & a little NADH
yield2 ATP2 NADH
like $$in the bank
4ATP
ENERGY INVESTMENT
ENERGY PAYOFF
G3PC-C-C-P
NET YIELD
10 reactions– convert
glucose (6C) to 2 pyruvate (3C)
– produces: 4 ATP & 2 NADH
– net: 2 ATP & 2 NADH
glucoseC-C-C-C-C-C
fructose-1,6bPP-C-C-C-C-C-C-P
DHAPP-C-C-C
G3PC-C-C-P
pyruvateC-C-C
Glycolysis Overview
DHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate
ATP2
ADP2
ATP4
ADP4
NAD+22
2Pi
enzyme
enzyme
enzyme enzyme
enzyme
enzyme
enzyme
enzyme
2Pi
2H
Alcohol Fermentation
1C3C 2Cpyruvate ethanol + CO2
NADH NAD+
Regenerates NAD can’t reverse the
reaction
•Bacteria• yeast
•Alcohol production
Reversible process With O2, lactate is
converted back to pyruvate by the liver
Lactic Acid Fermentation
pyruvate lactic acid3C 3C
NADH NAD+
O2
•Animals•anaerobic exercise (no O2)•Muscle cells•Acid lowers pH of cells (cramping)
Kreb’s (citric acid) cycle
Acetyl CoA
CO2
2 ATP!• electron carriers
– 6 NADH
– 2 FADH2
– go to ETC!
2 NADH, 2 CO2 2 Pyruvate
oxidative phosphorylation
O2
Photosynthesis
ETC of Photosynthesis
6
5
$$ in the bank…reducing power
to theCalvin Cycle
electron carrier
PGA6
3
6
1
5
3
Photophosphorylation
noncyclicphotophosphorylation
cyclicphotophosphorylation
STUDY!!