Topics 1 Carbon fixation Calvin Cycle 2 Regulation
Topics: 1. Carbon fixation: Calvin Cycle 2. Regulation of the Calvin Cycle 3. Photorespiration
ATP Light Reactions H 2 0 O 2 NADPH Carbon Reactions CO 2 CH 20 Julius Sachs (~1862): 6 CO 2 + 6 H 2 O + solar energy C 6 H 12 O 6 + O 2. Glucose/Starch
Calvin, Benson, Bassham (1950) C 14 CO 2 Hot ethanol
30 sec Malic acid Glucose Citric acid Aspartic acid PEP Sucrose Triose phosphates PGA Sugar-P Sugar-Di. P
5 sec Malic acid Citric acid PEP Triose phosphates PGA Sugar-P Sugar-Di. P
Which is the acceptor of CO 2? CO 2 ? 3 PGA H | H-C-OP | H-C-COOH | H
Which enzyme catalyzes this reaction? CO 2 Ribulose-1, 5 bisphosphate H | H-C-O-P | H-C=O | H-C-OH | H-C-O-P | H 2 x 3 PGA H | H-C-O-P | H-C-COOH | H
Phosphoenolpyruvate (PEP) 3 -Phosphoglyceric acid (3 PGA) STARCH Sugar-P Sugar-Di P Triose-P (Glyceraldehyde 3 - phosphate, Dihydroxyacetone) What is the order of these reactions? What do these reactions need? Where do these occur? Is all 3 -PGA converted to starch? What happens to the starch?
3 PGA 1, 3 -Bisphoglycerate Glyceraldehyde-3 -P Triose-P
Ribulose-1, 5 -Bis. P Triose-P
What happens to the Calvin cycle after a long period of darkness? Homework: How much NADPH and ATP is necessary to make 1 Triose-P?
Topics: 1. Carbon fixation: Calvin Cycle 2. Regulation of the Calvin Cycle 3. Photorespiration
Mechanisms of regulation of enzyme activities? a. Protein production/degradation b. Posttranslational reversible protein modifications c. Metabolites: “regular” metabolites regulatory metabolites
Regulation of the Calvin cycle? a. Rubisco protein production b. Light induction of Calvin cycle enzyme’s expression c. Enzyme activity: 1. Rubisco 2. Fru-1, 6 -bisphosphate phosphatase 3. Seduheptulose-1, 7 -bisphosphate phosphatase 4. Ribulose-5 -phosphate kinase 5. Glyceraldehyde-3 -phosphase dehydrogenase What is the common characteristic of all these reactions?
a. Rubisco production (s 8 L 8) s s s s L LL LL
Regulation of the Calvin cycle? a. Rubisco protein production b. Light induction of Calvin cycle enzyme’s expression c. Enzyme activity: 1. Rubisco 2. Fru-1, 6 -bisphosphate phosphatase 3. Seduheptulose-1, 7 -bisphosphate phosphatase 4. Ribulose-5 -phosphate kinase 5. Glyceraldehyde-3 -phosphase dehydrogenase Does light directly regulate this process? LIGHT
Rubisco activation RUBISCO -Activation: High p. H, Mg 2+, Rubisco Activase (redox) -Inactivation: Sugar-P, 2 -carboxyarabinitol-1 -phosphate
Rubisco activation Light Dark Stroma p. H Mg 2+ 8. 0 3 -6 m. M 7. 2 1 -2 m. M
The Ferredoxin-Thioredoxin System
Topics: 1. Carbon fixation: Calvin Cycle 2. Regulation of the Calvin Cycle 3. Photorespiration
The Problem with Oxygen Rubisco : Km (CO 2)= 8 -26 u. M Km (O 2)= 550 u. M Concentrations in solution (25 C): CO 2= ~12 u. M O 2= ~265 u. M
Ru. Bis Carboxylase/Oxygenase
Calvin Cycle Rib 15 bis. P (C 5) + O 2 3 -P-Glycerate (C 3) P-Glycolate (C 2) Glycerate (C 3) Glycolate (C 2) O 2 Glycolate (C 2) H 2 O 2 Glycolate (C 2) Glycine (C 2 -N) Glycerate (C 3) NH 4 Hydroxypyruvate (C 3) Serine (C 3 -N) CO 2 NH 4
Next Class: 1. CO 2 concentrating mechanisms 2. Starch and Sucrose synthesis
- Slides: 27