Photosynthesis

Hill Reagents

These are substances that accept electrons transferred from water by the photosynthetic light reactions and thus lead to evolution of oxygen up illumination.

The Hill reagent is NADP+, but some other chemicals can substitute for it in vitro

DCPIP - when this is added it can strip chloroplasts without NADP+, the reagent was decolourised and the chloroplasts began to produce oxygen even in the absence of carbon dioxide.

Calvin cycle

Has branches

Put in 18 Carbons as 6C3 which is rearranged to get 2C5

Ribulose biphosphate carboxylase/ oxygenase: The most abundant protein on earth + Slowest enzyme that we know of. Half of the nitrogen in our body comes from Nitrogen in Haber bosch process

16 sub unit protein composed of 8 large sub units coded by chloroplast DNA and 8 small sub units coded by Nuclear DNA

Physiological limits on photosynthesis

CO2 is absorbed by moist surfaces of the spongy parenchyma cells. Moist surfaces which gas dissolves into - loss a lot of water through evaporation in the process of CO2 absorption (Need a lot of water).

Plants have pores in the bottoms of their leaves to prevent water loss, this has an effect of CO2 absorption and O2 release

Water evaporation goes up exponentially as the heat rises = substantial problem global warming and crop growth

Light dependant reactions

Electrons go to reducing NADP (used in catabolism) to NADPH - is (used in anabolism)

Consequence of proton gradient is to generate ATP

As protons pass across the gradient the C10 cylinder rotates, as they do so they generate ATP

Chloroplast F0 domains have up to 15C sub units. F0 moves things around one click - allowing about 14 protons, giving 3 ATP

Phototroph can get energy but cant make 'stuff'

Light energy is absorbed by chlorophylls a and b

Once a photon hits the antenna it is transferred very rapidly to a reaction centre.

Light absorbed by chlorophyll is released rapidly as heat and fluorescence.

Antenna pigments are arranged in order light harvesting complexes LHC's, with pigments orientated so that energy of an exciton can easily be transferred to an adjacent pigment molecule etc. until it reaches a reaction centre

Reaction centre

the pair of chlorophyll a molecules are converted to a high energy state. As a result the redox potentials of the activated pigments are reduced. ( Kicks an electron from a low energy state to a high energy state)

NADPH is only useful as it is a strong reducing agent

Photosystem 2 comes first
photosystem 1 comes sescond

Redox carriers


Quinol reduced on one side of the membrane then oxidised- picks up proton as this happens and creates a proton gradient.

Photosystem 1 Uses iron sulfur proteins as its electron carriers instead of quinol

Electrons come from photosystem 1
these are carried to Photosystem 2, where they are converted to energy

cynobacteria get electrons from water

Oxygen is a waste product of photosynthesis. Iron Formation is product of increased oxygen in the atmosphere

Strip electrons away from water to make oxygen = complex of 4 manganese ions to produce that

Before this we had a reducing atmosphere

Now we have an oxidising atmosphere

It is estimated that PS increased global production of reduced carbon by 4500-45000 times