Photosynthesis

What are the general energy sources and outcomes in mitochondria and chloroplasts? Where do these conversions occur?

mitochondria:

• convert chemical bond energy from food to electrochemical gradient then chemical bond energy in ATP

chloroplast:

• convert light energy to electrochemical gradient then chemical bond energy in ATP

occur in internal membrane in mitochondria and chloroplast

What are the two major biochemical processes in photosynthesis?

1. energy transduction reactions: light captured and converted into chemical energy

2. carbon assimilation reactions: carbohydrates formed from CO2 and H2O

Name the structures of the chloroplast.

Outer membrane, inner membrane, intermembrane space, stroma, thylakoid membrane, grana, thylakoid lumen/space

What occurs when light hits a plant (photon)?

photon hits chlorophyll → unstable pigment molecule emits energy to adjacent molecule resonance energy transfer or passing excited electron to another molecule photochemical reduction

What does photosystem II contribute energy/ion wise? What does photosystem I contribute energy/ion wise?

Photosystem II: pumps H+ into thylakoid lumen

photosystem I: makes NADPH

What goes into and comes out of Photosystem II? What occurs in this process?

P680

• photoexcited electron passed to pheophytin (Ph, chlorophyll a) then passed to photoexcited P680 (chlorophyll a), plastoquinone (QA)

• QA passes electrons to QB and QB gets protons from stroma QBH2

• water is oxidized and split into hydrogen ions and oxygen

4 photons + 2H2O + 2QB + 4H+(stroma) → O2 + 2QBH2 + 4H+(lumen)

What occurs in the b6/f complex?

• QBH2 passes electrons and protons to cytochrome b6/f complex and transfers protons from stroma to thylakoid lumen

What goes into and comes out of Photosystem I? What are its products responsible for? What occurs in this process? What catalyzes this process?

P700

• receives electrons from PSII and excites them again with light then transfers to photoexcited P700, ferrredoxin

• ferredoxins transfer electrons to NADP+ → NADPH through photoreduction (in stroma)

  • NADPH needed for carbon reduction

  • enzyme responsible: FNR (ferredoxin-NADP+ reductase)

4Fd(Fe2+) + 2NADP+ + 2H+(stroma) → 4Fd(Fe3+) + 2NADPH

What goes into and comes out of ATP synthesis? What occurs in this process?

• in photophosphorylation, proton electrochemical gradient drives ATP synthesis through ATP synthase (CF0CF1)

What are the three phases of the Calvin-Benson cycle?

1. carboxylation of 3 ribulose 1,5-bisphosphate and generation of two 3-phosphoglycerate

2. reduction of 3-phosphoglycerate into glyceraldeyde 3-phosphate

3. regeneration of ribulose 1,5-bisphosphate

What enters and exits the Calvin Benson cycle? What are the energy outputs?

3 CO2 → 1 glyceraldehyde 3-phosphate

9 ADP + 6 NADP+

What happens in the first step of the Calvin Benson cycle and what catalyzes this?

• 3 CO2 enters and attaches to ribulose 1,5-bisphosphate

• RUBISCO

What happens in the second step of the Calvin Benson cycle?

• glyceraldehyde-3-phosphate formed

• portion of glyceraldehyde 3-phosphate leaves chloroplast (1 leaves 5 stays)

What happens in the third step of the Calvin Benson cycle?

• 5 glyceraldehyde-3-phosphate produces 3 ribulose-1.5-bisphosphate

What is the immediate product of photosynthesis? What can this product be used for?

glyceraldehyde 3 phosphate

can be used immediately or stored as starch or make sucrose