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

Melvin Calvin

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