PhotosynthesisChapter 10
Photosynthesis occurs in the chloroplast.
Chloroplast = type of plastid
Proplastid
ChloroplastsChromoplastsAmyloplasts
When photosynthetic pigments absorb photons, four things can happen:
Photon re-emission (fluorescence)
Heat generation
Energy transfer (resonance transfer)
Photochemistry
Pigments absorb across specific wavelengths.
Multiple pigments allow more light to be harvested.
Absorption Spectrum
Pigment molecules are organized into antenna complexes.
Two types of antenna complexes with distinct reaction centers:
RC absorbs at 700 nm (PS I)
RC absorbs at 680 nm (PS II)
PS IInvolved with the reduction of NADPH for use in carbohydrate synthesis
PS IIInvolved with ATP synthesis for use in carbohydrate production
Two Distinct Photosystems
Photosystems I and II
Electrons come from the splitting of water.
H2O ½O2 + 2H+ + 2e-
2H2O O2 + 4H+ + 4e-
Photosystems I and II
Photosystems I and II
Photophosphorylation Summary
PS II 4 photons ~2 ATPPS I 4 photons 2 NADPH
Photosynthesis Overview
Process of CO2 fixation = Calvin Cycle
The Calvin cycle takes place in the chloroplast stroma.
Calvin cycle has three main parts:
CarboxylationReductionRegeneration
Glyceraldehyde-3-P
Ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco)
1/8 - 1/4 total leaf protein
Glyceraldehyde-3-P
3 Ribulose-1,5-bisphosphate + 3 CO2
3 Ribulose-1,5-bisphosphate + Glyceraldehyde-3-phosphate
Fixation of 1 CO2 molecule requires 3 ATP + 2 NADPH
Summary