photosynthesis

PhotosynthesisPhotosynthesis

Let the sun shine…..Let the sun shine…..

Hooray for photosynthesis!!!!Hooray for photosynthesis!!!!

The equations…The equations…

Cellular respiration-highly exergonicCellular respiration-highly exergonic C6H12O6 + O2 C6H12O6 + O2 CO2 + H2O + ATP!! CO2 + H2O + ATP!! Energy released thru oxidation of glucoseEnergy released thru oxidation of glucose

Photosynthesis-highly endergonicPhotosynthesis-highly endergonic Light + CO2 Light + CO2 C6H12O6 + O2 C6H12O6 + O2 Light energy used to reduce CO2Light energy used to reduce CO2

StromaStroma ATP produced in stromaATP produced in stroma Calvin cycleCalvin cycle

Thylakoid membraneThylakoid membrane Photosystems Photosystems

embeddedembedded ETCsETCs ATP synthaseATP synthase

Thylakoid spaceThylakoid space H+ conc. gradientH+ conc. gradient

OverviewOverviewProduce energyRequired for darkreactions

“fix” CO2 into glucose

Highly endergonic

Light dependent reactionsLight dependent reactions Occur in thylakoid space & membraneOccur in thylakoid space & membrane Light strikes chlorophyllLight strikes chlorophyll E- are boosted to higher energy level & travel down E- are boosted to higher energy level & travel down

an ETCan ETC Released energy captured to form ATP & NAPHReleased energy captured to form ATP & NAPH Water molecules borken apart to replace lost e-Water molecules borken apart to replace lost e-

Light independent reactions-carbon fixingLight independent reactions-carbon fixing Uses energy captured in ATP & NADPH to reduce Uses energy captured in ATP & NADPH to reduce

CO2 to sugarCO2 to sugar Occurs in stromaOccurs in stroma

Absorption pigmentsAbsorption pigments Light energy must be absorbed Light energy must be absorbed

to be of any benefitto be of any benefit Pigments absorb certain Pigments absorb certain

wavelengths of light, which wavelengths of light, which causes altered structurecauses altered structure

Chloroplasts contain several Chloroplasts contain several pigmentspigments Chlrophyll-absorbs violet, blue, Chlrophyll-absorbs violet, blue,

redred Carotenoids-absorb blue & greenCarotenoids-absorb blue & green Phycocyanins-absorb greenPhycocyanins-absorb green

What happens when chlorophyll absorbs What happens when chlorophyll absorbs light?light?

An e- becomes energized & moves to higher orbitalAn e- becomes energized & moves to higher orbital This is unstable-e- will normally release energy & This is unstable-e- will normally release energy &

move back to its original orbitalmove back to its original orbital In photosynthesis, e- is captured by ETCIn photosynthesis, e- is captured by ETC

What is a photosystem?What is a photosystem?

Located in thylakoid membraneLocated in thylakoid membrane Composed of a reaction Composed of a reaction

center(chlorophyll), ,accessory(acenter(chlorophyll), ,accessory(antennae) pigments, & an ETCntennae) pigments, & an ETC

PSI-PSI- evolved 1evolved 1stst, , cotains a dimer of chlorophyll,cotains a dimer of chlorophyll, can operate independently of PSII, can operate independently of PSII, its ETC makes NADPHits ETC makes NADPH

PSIIPSII Supllies e- to PSISupllies e- to PSI ETC produces ATP ETC produces ATP

(photophosphorylation)(photophosphorylation) Accessory pigments absorb light Accessory pigments absorb light

& pass it chlorophyll& pass it chlorophyll

•Only chlorophyll loses e- to ETCs

Light causes e- to become energized in PSIIJump to higher level

Water is split to replace e-

E- captured by cytochromes in ETC

Energy used to push H+ from stroma to space

Gradient used to produce ATP in stroma

E- end up in PSI, which has also lost e-To its ETC

PSI ETC gives its e- to NAD-an e- shuttle, it carries e- to calvin cycle

Cyclic e- flow-used when no NADP is available-Cyclic e- flow-used when no NADP is available-(calvin cycle uses ATP faster than NADPH)(calvin cycle uses ATP faster than NADPH)

This ETC shuts downNo NADPH or O2

RuBP is regenerated

RuBP carboxylase

Reverse reactions of glycolysis

CO2 is reduced

G3P