Lecture 34: Photosynthesis-light reactions

Question 1

what initiates light reactions in photosynthesis?

Answer 1

absorbance of light

Question 2

consequence of electron transfer reactions in light reactions?

Answer 2

1) production of QH2 or NADPH (NADH)
2) translocate H+ and generate a proton gradient across a membrane-used for ATP synthesis
3) in cyanobacteria and plants, O2 is produced from H20

Question 3

why is it called Dark reactions

Answer 3

don’t require light

Question 4

Subsequent to the light reactions…. dark reactions…

Answer 4

• biosynthesis that uses the ATP and NADPH to fix CO2 as 3-phosphoglycerate
• 3-phosphoglycerate is used then to make C4 to C7 sugars

Question 5

What wavelength does visible light contain?

Answer 5

700nm (red) to 400 nm (dark blue)

Question 6

Types of Photosystems

Answer 6

PS II
PS I
Complex PsI and PSII
PS1 + PSII

Question 7

PS II

Answer 7

• in purple and green filamentous bacteria
• type II reaction center with P870 chlorophyll
• works with cytochrome bc1 complex in a cyclic system
• There is a H+ translocation but not net production of NADPH

Question 8

PSI

Answer 8

-in green sulfur bacteria
-type 1 reaction center with P700 chlorophyll
-works either with cytochrome bc complex in a cyclic system without net production of NADPH
OR
with an electron done such as H2S or S2O32- with net production of NADPH

Question 9

Complex PSI + PSII

Answer 9

in cyanobacteria

• photosystems act in series
• works with cytochrome bf complex
• organisms use H2O as source of electrons to reduce the primary pigment in PSII with a net production of NADPH

Question 10

PSI+ PSII

Answer 10

in plants

• both systems act in series
• work with cytochrome bf
• H2O is used as source of electrons with net production of NADPH