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!!