http://web.pdx.edu/~rueterjesr473/notes/photosynthesis-overview.htm

Photosynthesis Overview

This section will focus on the light and dark reactions of photosynthesis. We will catalog the biochemical composition of these two components of cell machinery and follow the reactions that tie them together. This section will introduce the important concept of "optimization" in relationship to the relative amounts of the photosynthetic membrane to the photosynthetic enzymes. We will expand on optimization in subsequent sections. We will examine the overall output of photosynthesis as a function of light and work with the equations and graphs that describe this relationship. You should reach an understanding for intraspecific and interspecific variations in photosynthetic component content as it relates to photosynthesis output.

Steps

pigments absorb light energy

transformed to chemical forms (ATP and NADPH)

passed to enzymatic, RPPP cycle synthesis of triose

some energy used for reductive assimilation of nitrogen sources

trioses are both stock for synthesis and to provide energy for respiration

adaptation through differentical synthesis

 

Biological components in a little more detail

see the list under biochemical composition

PSII

plastoquinone

cytb6f complex

PSI

coupling factor

RuBisCO

Reductive Pentose Phosphate Pathway enzymes

 

Processes

photosynthesis contains several types of energy transduction

photon capture to form excited molecules

resonance transfer of energy

fluorescence loss of energy

charge separation (voltage potential of the e-)

proton pumping in the thylakoid membrane

chemiosmotic production of ATP

reduction of Fd and NADPH

reduction rxns in RPPP

light dependent reactions (photon to NADPH, Fd(red) and ATP)

RPPP CO2 + NADPH + ATP --> reduced carbon (as TrioseP)

associated storage reactions (glycogen and starch)

photorespiration (RuBP + O2 --> 2C and 3C + rearrangement of these)

photoinhibition (light dependent inhibition of photosynthesis that takes protein synthesis to reverse)

 

net output

P vs. I

Pmax, Ik, I0

Blackman model

tanh model - Pmax, alpha, beta, respiration

 

Regulation

substrate level control by NADPH and NADP+

roles of ferredoxin and ions in regulation in the chloroplast

activation of RPPP enzymes

 

Optimization

balance of flow from light dependent to light-independent reactions

2 component model - increase limiting component (photo-memb or RPPP enzymes)

 

Adaptation to the environment

examples of how cells have more or less of photosynthetic membranes or RPPP enzymes in adaptation to low or high light respectively

 

April 10, 2000