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Biochemistry Exam 3


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What is the result of light reactions?
oxidation of water, reduction of NADP+, generation of proton gradient that powers ATP synthesis
Net result of cytochrome b6f cycle
for every two electrons coming from Photosystem II, four protons are released into thylakoid lumen
How many protons are pumped into thylakoid for each O2 molecule
Noncyclic electron flow
Electrons are transfered from water, through Photosystem II through cytochrome b6f, PS I, and then to NADP+
Does photosystem I contribute to proton gradient?
No, except by consuming stromal proteins in reduction of NADP to NADPH
Cyclic electron flow
Electrons from PS I do not reduce NADP+ but return to cytochrome b6 f, then transfered to plastocyanin, and back to PS I to reduce P700*
Does cyclic electron flow require energy input?
requires input of light energy at PS I but not PS II
Is NADPH formed in cyclic electron flow
No, free energy is not recovered but concerved in the form of proton gradient in cytochrome b6f
coupling of dissipation of proton gradient to the phosphorylation of ATP
what provides free energy to drive ATP synthesis
movement of protons from lumen to stroma
What does RUBISCO do
catalyzes CO2 fixation by adding CO2 to a five carbon sugar and then cleaving product into 2 3 carbon units.
What is the energy cost of fixing one CO2
3 ATP and 2 NADPH
What are the properties of all metabolic pathways
1. Each step is catalyzed by distinct enzyme
2. The free energy consumed or released in certain reactions is transferred by molecules such as ATP and NADH
3. Rate of pathway can be controlled by altering activity of individual enzymes
4.Many metabolic pathways have a similar irreversible step near the start that commits metabolite.
What is the yield of glycogenolysis
glucose -1-P
What does an active site of aldolase contain
a LYS residue that forms a Schiff base (imine)with the substrate, and ionized Tyr residue that acts as a base catalyst
Why does a reaction proceed if G>0
Products are quickly removed
What is the difference between pentose phosphate pathway and glycolysis
It produces NADPH rather then NADH
Covalent catalysis
covalent bond forms between catalyst and substrate during formation of transition state
Metal Ion Catalysis
Metal ions mediate oxidation-reduction reactions or by promoting the reactivity of other groups in the enzymes active site through electrostatic effects.

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