Lecture 10 Exam 3 Matl

Question 1

Where does photosynthesis take place in plants?

Answer 1

In the thylakoid membrane of the thylakoid, which is a compartment of the chloroplast

Question 2

Describe the important thylakoid locations in photosynthesis

Answer 2

Stroma (N-side)
Thylakoid membrane (where photosystems are)
Lumen (P-side) where protons build up before going down ATP synthase

Question 3

Describe the reaction at the first location in photosynthetic electron transport

Answer 3

PSII gets excited by light. An oxygen-evolving complex splits water into oxygen gas. An excited P680 converts it into a good electron donor, so it donates e- to pheotin, which gives an electron to QA, which then gives its electron to QB. The chain goes again, reducing QB to QBH2. Water donates two protons to QBH2. QBH2 donates 2 protons for transport to the lumen. 2 protons from the stroma also get transported

Question 4

Describe the reaction at the second location in photosynthetic electron transport

Answer 4

PSII transfers e- to cytochrome b6f, which then donates electrons to plastocyanin

Question 5

What happens at the third location in photosynthetic electron transport?

Answer 5

Plastocyanin donates electrons to P700 in PSI. Light excites P700, which then donates e- to A0 (chlorophyll a). Charge separation causes P700+ to get electrons from plastocyanin again. A0- is a strong reducing agent that gives its e- to phylloquinone (Qk). 3 Fe-S proteins get e-, which then go to ferrodoxin, which then goes to ferrodoxin: NADP+ oxidoreductase. NADP+ then gets reduced to NADPH

Question 6

Describe cyclic electron flow

Answer 6

PSII gets bypassed, no oxygen is evolved, and no NADPH is produced. However, protons are pumped and ATP is made. Protons are pumped across the thylakoid membrane. More ATP is made as a result, compared to noncyclic electron flow. Ferrodoxin recycles e- back go cytochrome b6f, which passes them off to P700, which goes back down the chain to ferrodoxin again

Question 7

How are electrons recycled in cyclic electron flow?

Answer 7

Ferrodoxin in PSI transfers e- back to cytochrome b6f, which then transfers to plastocyanin, then P700 again. This pumps protons, so ATP is still made

Question 8

Describe noncyclic electron flow

Answer 8

It’s the linear transfer of electrons to produce NADPH and evolve oxygen gas. For every two photons absorbed at PSII, one electron reduces NADP+ to NADPH