Photosynthesis…life’s basic Rx!

Basic questionsSome historySome plant anatomySome biochemistry light reactions dark reactions photolysis

Basic questions??

What do plants eat?Why do plants need light?Why do plants need water?Why are plants green?

Some History…Greeks to …?“what do plants eat”?VanHelmont’s tree…Priestly & phlogiston…Lavoisier lost his head over some O2…well?Englemann & bacteria?Melvin Calvin 1948!

Summary of photosynthesis ???CO2, H2O and light go in…Carbohydrate and O2 come out

6CO2+6H2O

C6H12O6+O2

Anatomy of a leaf

Function(s)??Collect sunlightMake ‘food’Move food to storageThus…Structure related to function…

WHY ARE LEAVES GREEN???

ENLARGE

Summary of the chloroplast

Double membranesThylakoid disks called grana (chlorophyll)

StromaETS‘loose’ enzymes

2 sets of photosynthetic reactions

Light dependentLight energy captured3 reactions

Light independentCalvin cycleMakes pyruvate (C3)

What is light?What are photons?Energy & photons

What is chlorophyll?

Plant pigmentImbedded in membrane of thylakoid disks

Why green?

What colors are absorbed?What colors reflected?

QUIZ

Why are leaves green?Relate chloroplast to mitochondriaWhat is chlorophyll?What cell organelle contains chlorophyll?

How is light ‘captured’?

How to ‘grab’ a photon?

How to ‘hold onto’ the ‘hot potato’ (energy of photon)

Quiz

What are the ‘ units’ of light?What colors are ‘captured’?How are photons ‘captured’?

3 light dependent reactions

Photosystem I…cyclic photophosphorylation

Photosystem II…noncyclic photophosphorylation

photolysis

The Light Reactions (light dependent)

Cyclic Photo-phosphorylation (photosystem I)Noncyclic Photo-phosphorylation (photosystem II)Photolysis

Cyclic photophosphorylation

Cyclic photophosphorylation

Photon ‘excites’ e-e- ‘absorbed’e- passed thru ETSATP generated via chemiosmosise- ‘recycled’

Quiz

What’s produced in photo I?How is ATP made?What happens to the electron?

ATP

Chemiosmosisrecycled

Noncyclic photophosporylation

NADHOxygenATP (chemiosmosis)Electron IS NOT recycled

Quiz: photosystem II + photolysis

What is made?

How is ATP made?

What is the importance of O2?

ATP, NADPH, O2

Chemisosmosis

Free oxygen released thus changing the world…why??

Products of light reactions

ATP (via chemiosmosis)NADPHOxygenWhat happens to these? And…What about night?

What happens during ‘dark’ Rx (light independent reactions)

CO2 from air is ‘fixed’…ATP & NADPH carry energy from light RxC3…pyruvate (PGA) is formed2X ‘turns’=C6…?C6>organic ‘stuff’

The Calvin-Benson Cycle

How to store ATP?Why reinvent the wheel?Long-term storage?

Calvin cycle

Quiz-Dark reactions (Calvin cycle)

Why are these reactions called ‘dark’What are the products of the Calvin cycle?Where in the chloroplast do these Rx occur?What kinds of molecules can be made from PGAL (pyruvate)?What is the most prevalent protein on the planet? Why is it so important?

Alternative pathways??

Why is the former called C3pathway?photorespiration…?C4…CAMNot as efficient as C3 but, hey….beats nothing?

Photosynthesis summary

Energy flow in nature

Energy pathways in photosynthesis