Lecture 15: photosynthesis

Question 1

where do plants get the carbon they consume during photosynthesis

Answer 1

through their leaves from the gaseous carbon dioxide in the air

Question 2

matter equation of photosynthesis

Answer 2

6CO2 + 12H2O -> C6H12O6 + 6O2 + 6H2O

Question 3

Two stage flow of energy in photosynthesis

Answer 3

1. Light reactions: splitting of water and chemiosmosis
   - radient energy ->
   - chemical bonds of ATP, NADPH
2. carbon fixation and reduction reactions
   - chemical bonds of ATP, NADPH ->
   - chemical bonds of glucose

Question 4

two stages of PSN

Answer 4

Stage 1 (Light reactions): conversion of light energy into the chemical bond energy of ATP and reduced NADPH

Stage 2 (carbon fixation reactions): reduction of CO2 by energy stored in ATP, NADPH

Question 5

During the light reactions water is oxidized to O2. Where did the hydrogens go?

Answer 5

• used in the reduction of NADP+

- used in the synthesis of ATP by chemiosmosis

Question 6

photosystems

Answer 6

• light harvesting protein complexes found in the thylakoid membrane
  1. photon excites electrons of pigments
  2. excitation is transferred to the reaction center chlorophyll
  3. reaction center chlorophyll is oxidized to Chl+ as it donates an electron to a primary electron acceptor

Question 7

Photosystem II

Answer 7

• electron “hole” in PSII is filled by the oxidation of water
• electron travels away from PS II to an ETC
• chemiosmotic synthesis of ATP

Question 8

Photosystem I

Answer 8

• electrons traveled away from PSI and eventually reduces NADP+ to NADPH
• electron “hole” of PSI is filled by electron lost by PSII
• PSII and PSI are adjacent in the thylakoid membrane

Question 9

which of the following correctly describes the linear pathway of electrons in the light reactions of photosynthesis

Answer 9

H2O to PS II to PS I to NADP+

Question 10

phosphorylation

Answer 10

couples the energy of photons to the phosphorylation of ATP

Question 11

Cyclic phosphorylation

Answer 11

PSI can also provide energy for synthesis of ATP

Question 12

what does cyclic electron flow of PS I generate

Answer 12

ATP only

Question 13

step 2 of photosynthesis

Answer 13

Carbon fixation reactions

• reduce CO2 to sugrars
• convert energy of ATP and NADPH to energy of chemical bonds of glucose
• occurs in the storm of chloroplasts and in the cytosol of prokaryotes

Question 14

Calvin cycle steps

Answer 14

1. carbon fixation
2. reduction and sugar formation
   regeneration of CO2 acceptor

Question 15

Step #1: carbon fixation catalyzed by rubisco

Answer 15

• addition of 1 CO2 to 5 Carbon acceptor molecule (RuBp)
• product is 2 molecules of 3 carbon each
• rubisco is slow, catalyzes about 2-3 reactions per second
• most abundant protein on earth

Question 16

Step #2: reduction of 3PG to triode phosphate: G3P

Answer 16

• involves ATP and NADPH
• product is reduced to G3P
• G3P can be
  
  1. converted to glucose
  2. converted to starch
  3. used to regenerate RuBp

Question 17

Step #3: regeneration of RuBp

Answer 17

• complex

- energy requiring