Micro 14

Question 1

Photosynthesis

Answer 1

• Use of light energy to drive biosynthesis
• photosynthetic autotrophs = photoautotrophy

Question 2

Light reactions

Answer 2

Convert light energy into chemical energy (proton motive force and ATP)

Question 3

Dark reactions (light-independent reactions) fix CO2

Answer 3

• Require ATP and reducing power (NADPH)
• Oxygenic photosynthesis: Water is electron donor and O2 is waste product (H2O to O2)
• Anoxygenic photosynthesis: other electron donors used, does not produce O2 (H2S to SO4)

Question 4

Light-sensitive pigments

Answer 4

• Chlorophylls (in plants, algae, cyanobacteria), transmits green light and absorbs red and blue (CH2=CH)
• Bacteriochlorophylls (in anoxygenic phototrophs)(CH3-C=O)

-to absorb light and start energy conversion, located in photo complexes

• Pigment diversity is ecologically important, allows different phototrophs to absorb different wavelengths and coexist in same habitat

Question 5

Antenna Pigments

Answer 5

• (large numbers of chlorophylls/bacteriochlorophylls) surround and funnel light energy to reaction centers

Question 6

Light-Harvesting and Reaction centers

Answer 6

(a) Light energy absorbed by light-harvesting (L H) molecules (light green) is transferred to the reaction centers (R C) where photosynthetic electron transport reactions begin
LH2 -LH1- RC

Question 7

Chlorosomes

Answer 7

• Chlorosomes capture low light intensities
• transfers light energy through FMO proteins to bacteriochlorophyll a in reaction center
• Chromosomes allow phototrophs to grow at very low light intensities: example deepest waters

Question 8

Carotenoids

Answer 8

• most widespread accessory pigments
• function primarily as photoprotective agents
• Quenching reactive oxygen species (ROS)
• Preventing dangerous photooxidation

Question 9

Phycobiliproteins

Answer 9

• main light-harvesting systems of cyanobacteria and red algae chloroplasts
• gives organisms their characteristic colors
• Allow cells to grow at lower light intensities

Question 10

Anoxygenic Photosynthesis

Answer 10

• similar to respiration
• generates proton motive force
• requires photosynthetic reaction centers
• Antenna pigments funnel light energy to reaction center to excite special pair, producing electrons for electron transport
• Two classes of reaction centers: quinone type (Q-type) and iron-sulfur type (FeS-type)

Question 11

Quinone type

Answer 11

• Q type reaction center
• contains three polypeptides (L,M,H)
• L,M, and H bind four molecules of bacteriochlorophyll a (special pair + two that transfer electrons within reaction center)
• light energy –> transferred to and excites special pair, generating a strong electron donor
• Electrons flow through low E to High E and generate proton motive force

Question 12

Cyclic Photophosphorylation

Answer 12

• Electrons cycle within closed loop

Question 13

Oxygenic Photosynthesis

Answer 13

• Use both FeS-type and Q-type reaction centers
• PS1 and PS2 interact in ‘Z scheme’ of photosynthesis