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58 Cards in this Set

  • Front
  • Back
What is the main purpose of photosynthesis?
-to reduce CO2 to the level of carbs using water as reducing agent
What are the First Principles of Photosynthesis?
1) must be a reduction
2) must be a biological reduction
3) must be a biological reductant
4) this reduction will require energy AND be regeneratable
Are photochemical reactions affected by temperature?
-no, they're really fast no matter what
Are chemical reactions affected by temperature?
-yes, if you lower temp then required "dark" period becomes longer
What was the purpose of the flash experiment?
-to see optimal oxygen production
-occured over 100 ms or more
What occurs in a light reaction?
-H+ derived from water is used in chemiosmotic synthesis of ATP
-Hydride ion (H:-) from water reduces NADP+ to NADPH
-Release of O2 from splitting 2 water molecules
What occurs in a dark reaction?
-reduction of gaseous CO2 to carbohydrate
-requires energy of NADPH and ATP
Can light and dark reaction occur at the same time?
-sum: CO2 + H20 = (CH2O) + O2
What is the redox potential of NADP+?
How about the free energy?
Wavelength of 680?
- (-1.14V)
- +220 kJ/mol
-175 kJ/mol
What is the equation for light energy?
- E=hv
What happened with the Red drop?
-light was absorbed in the red-light spectrum but couldn't be used effectively in the far red wavelength
-if combined with shorter wavelength, more O2 is created than the sums of the two individualy
-this supported the idea of two photosystems
What connects the two photosystems?
-cytochrome bf complex
How are electons conducted in the two photosystems?
-conducted from water to NADP+
Where are the proteins and pigmnets found for the two photosystems?
-in the thylakoid membrane
How many subunits are in Cyt. bf?
-over 10
-over 25
What is a reaction center in the photosystems?
-The site of photochemical reaction in both PSI and PSII.
What is a special pair?
-two chlorophylls in each reaction center that are energized by light
In PSI, what is the special pair?
What is the Z-scheme?
-path of electron flow and reduction potentials of the components in photosynthesis
What does the Z-scheme do?
-absorption of light energy converts P680 and P700 to excited molecules (from poor to good reducing agents)
-light energy drives electron flow uphill
-NADP+ is ultimately reduced to NADPH
In PSII, where do the electrons for transport come from?
How are the electrons moved through Cytochrome bf?
-oxidation of water
-catalyzed by the oxygen-evolving complex
What is P680?
-special pair pigment of PSII
-reduced by electron derived from oxidation of water
-increased reducing power from light energizing
What happens with PSI energizing?
-reduced P700 is excited to P700* which then donates an electron through a series of acceptors to ferredoxin (Fd)
-reduction of NADP+ by Fd
What catalyzes the reduction of NADP+ by Fd?
-ferredoxin-NADP+ oxidoreductase (on the stromal membrane side)
What is photophosphorylation?
-synthesis of ATP which is dependant upon light energy
What are the two major particles of Chloroplast ATP synthase?
Where is CF0 and why?
How about CF1?
-CF0 spans the membrane, forms a pore for H+
-CF1 protrudes into the stroma and catalyzes ATP synthesis from ADP and Pi
What does cyclic electron transport yeild?
-ATP but no NADPH
*thus balancing the need for 3 ATP for every 2 NADPH
What is the difference in cyclic electron flow in terms of ferredoxin?
-Fd donates e- back to the PQ pool via a specialized cytochrome (instead of NADP+)
How does cyclic flow increase the protonmotive force?
-increases it
*also increases ATP but no NADP+ is produced
What powers Dark reactions?
-ATP and NADPH (formed during light reactions)
Where do dark reactions occur and in what cycle?
-chloroplast stroma
-reductive pentose phosphate cycle (RPP cycle)
What are the three basic steps of a dark reaction?
1) fixation of atmospheric CO2
2) Reduction of CO2 to carbohydrate
3) Regeneration of the molecule that accepts CO2
What is the net equation for the RPP cycle?
3CO2 + 9ATP + 6NADPH + 5H20 yields 9ADP + 8 Pi + 6NADP + Triose phosphate
What does Rubisco stand for?
-Ribulose 1,5-Bisphosphate Carboxylase - Oxygenase
What is Rubisco?
-makes up about 50% of soluble protein in plant leaves
-one of the most abundant enzymes in nature
-8 large and 8 small subunits
What does Ribulose 1,5-bisphosphate create with CO2?
-2 molecules of 3-phosphoglycerate
When is Rubisco active?
-in the light
-in the dark
What causes activation of Rubisco when in the light?
What inhibits it at night?
-CO2, MG2+, and correct stromal pH
-2-Carboxyarabinitol 1-phosphate
What is the RPP cycle also known as?
What are the three stages of the RPP cycle.
-Calvin Cycle
1) carboxylation
2) reduction
3) regeneration
What catalyzes carboxylation in the RPP cycle?
What happens in the reduction stage of RPP cycle?
-3-phosphoglycerate converted to glyceraldehyde 3-phosphate (G3P)
What happens in the regeneration step of RPP cycle?
-most of G3P is converted to ribulose 1,5-bisphosphate
At night, how is the RPP cycle regulated?
-oxidation of surfaceexposed -SH groups on some RPP enzymes inactivates them, preventing CO2 assimilation
-catabolism of starch via glycolysis and TCA cycle provides energy
How is RPP cycle regulated in daytime?
-Thioredoxin is reduced by photosynthetic electron transpor
-reduced thioredoxin reduces disulfides to -SH, activating some RPP enzymes
-Stromal Mg2+ and pH increase as protons translocated into lumen, activating fuctose 1,6-bisphosphatase and sedoheptulose 1,7-bisphosphatase
Rubisco aids carboxylation 70% of the time. What else can it be used for?
-it uses O2 to catalyze an oxygenation reaction which competes with the carboxylation reaction (photorespiration)
Is oxygenation better than carboxylation?
-no, it is 1/3 to 1/4 of carboxylation
What does photorespiration consume?
How about produce?
-glyoxylate, serine, glycine, and CO2
What occurs in oxygenation (write names rather than formula)?
-Ribulose 1,5-bisphosphate catalyzed by Rubisco to form one molecule of 2-phosphoglycolate and one molecule of 3-phosphoglycerate
What is a benefit of photorespiration?
-it salvages 3/4 of carbon that would normally be lost
What is the C4 pathway?
-C4 plants use this to ensure only carboxylation occurs and never oxygenation
-it uses a 4 Carbon sugar
-uses ATP to bring 4 carbon sugar into cell and drop it directly next to Rubisco ensuring it gets used
-splits in space (close to rubisco)
What is CAM?
-Crassulacean acid metabolism
-found in succulents and helps conserve water in dry climates
-splits in time
What is the initial product of carbon-fixation in C4 plants?
Where does this occur?
-mesophyll cells
What is a similar feature of both C4 pathways and CAM?
-both can run with stoma closed
-both form oxaloacetate and then malate
What happens to the malate in C4 plants?
Then what?
-it enters bundle sheath cells and converted to CO2, Pyruvate, and NADPH
-CO2 enters Calvin cycle, pyruvate enters mesophyll cells and reacts with ATP to regenerate starting material
What happens in CAM plants?
-CO2 fixation occurs at night when stoma are open
-fixed into oxaloacetate which is converted to malate and stored in vacuoles
-in daytime, stoma close and stored CO2 is removed from malate and put into calvin cycle
Why are C4 plants said to be split in space?
-all Rubisco occurs in bundle sheath cells and occurs with or without stoma open (usually closed)
Why are CAM plants said to be split in time?
-CO2 fixation only occurs at night
-it is stored as malate until daytime when it converts it to energy for growth and CO2 production