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Description
Flashcards by Candice Young, updated more than 1 year ago
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Created by Candice Young
over 6 years ago
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| Question | Answer |
| Dark reaction of photosynthesis | Reaction where ATP and reducing power generated by light reaction are used to reduce CO2 into carbohydrates |
| Different CO2 reduction cycles | 1) Calvin Cycle - 99% of CO2 fixation happens by this; aerobic 2) Reductive (reverse) TCA Cycle; anaerobic 3) Reductive acetyl-CoA pathway; anaerobic 4) 3-Hydroxypropionate Cycle; anaerobic |
| Basic principles in Calvin Cycle Experiment | t = 0: 14CO2 radioisotope injected into lollipop-shaped growth chamber containing Chlorella at specific intervals: samples removed from chamber after the addition of 14CO2 via the stopcock at the bottom Chlorella in samples killed instantly --> look where 14C had gone |
| Detection of first compounds in Calvin experiment | observe compounds present at different intervals using thin layer chromatography and autoradiography (looking for biggest concentration of C14 --> 3 phosphoglycerate (PGA) found to be first stable intermediate of cycle |
| Basic Steps of the Calvin Cycle | 1) Carboxylation 2) Reduction 3) Regeneration |
| Carboxylation step of Calvin Cycle | 1 CO2 added on to RBP by enzyme RuBisCO --> forms PGA --> ATP from light reaction put in to make a phosphoglycerate |
| Reduction Step of Calvin Cycle | phosphoglycerate of first step reduced by NADPH of light reaction to form GAP --> forms fructose that undergoes various pathways (outside cycle) or a glyceraldehyde phosphate (within cycle) |
| Regeneration Step of Calvin Cycle | glyceraldehyde sugar rearranged to another sugar, PRK enzyme uses energy to form RBP again and start cycle over |
| RuBisCO | ribulose biphosphate carboxylase carboxylation step RBP + ATP + CO2 --> PGA *once you add the CO2, the intermediate product is really unstable, it actually breaks down and gets hydrolyzed while on the enzyme* |
| PRK | phosphoribulose kinase regeneration step Ribulose 5-phosphate + ATP --> Ribulose 1,5-biphosphate *PRK phosphorylates and regenerates reactant to go back to the center* |
| Competing reaction with carboxylation | instead of phosphorylating RBP, can use O2 as competing substrate to produce 1 PGA and 1 phosphoglycolate (toxic) usually isn't a problem because carboxylation is so fast but is dangerous in high temperatures (aqueous solubility of CO2 decreases below O2) |
| How do photosynthetic organisms achieve high enough [CO2] for RuBisCO to function properly? | Use carbon concentrating mechanisms that are performed within the carboxysomes (of cyanobacteria) |
| carboxysome | polyhedral protein shell compartments containing highly concentrated array of RuBisCO and carbonic anyhdrase (CA) CO2 can’t dissolve OUT of the protein shell like it can through lipid membranes! meanwhile, O2 doesn't diffuse very well IN |
| carbonic anhydrase | converts HCO3- to CO2 |
| carbon concentrating MECHANISMS | 1) High-affinity importers of CO2 + HCO3- expressed if CO2 concentrations low 2) HCO3- accumulates in cytoplasm --> diffuses into carboxysome 3) HCO3- --> CO2 by carbonic anhydrase ONLY in the carboxysome 4) CO2 used rapidly by RuBisCO 5) O2 excluded by shell proteins |
| Reverse Citric Acid (TCA) Cycle | performed by green sulfur bacteria Fdred fixes CO2 (enters at multiple points of cycle UNLIKE Calvin cycle) ATP drives reaction enzymes are same EXCEPT for fumarate reductase and ATP citrate lysase (diagnostic) occurs in chlorosomes |
| Net reaction of Reverse TCA Cycle | 3CO2 + 12H + 5ATP --> C3H6PO3^2- +3H20 |
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