Photosynthesis

CHLOROPLASTS

Site of Photosynthesis

Double Membrane

Interior space called the STROMA

Columns of membrane bound sacs

Sacs = Thylakoids

Stacks = Grana

Membrane holding together Thylakoids & Grana is called the LAMELLAE

THYLAKOID

MEMBRANE

THYLAKOID SPACE

or

LUMEN

PIGMENTS ARE IMBEDDED IN THE MEMBRANE IN CLUSTERS CALLED PHOTOSYSTEMS

REMEMBER THAT VISIBLE LIGHT IS ONLY A SMALL PORTION OF THE ENERGY COMING FROM THE SUN

THE AMOUNT OF ENERGY IN LIGHT IS DETERMINED BY ITS WAVELENGTH THIS ALSO DETERMINES THE COLOUR OF LIGHT

THE JOB OF PIGMENTS IS TO ABSORB SPECIFIC WAVELENGTHS OR PHOTONS OF LIGHT. THIS ENERGY IS TRANSFERRED TO ELECTRONS THESE ‘catching’ PIGMENTS ARE CALLED ANTENNA COMPLEXES

PHYTOL TAIL

ANCHORS PIGMENT INTO THE THYLAKOID MEMBRANE

PORPHRYIN RING

CENTRAL Mg

ABSORBS LIGHT ENERGY AND TRANSFERS IT TO AN ELECTRON

PHOTOSYNTHESIS OVERVIEW

THE EXCITED ELECTRONS THEN TRANSFER ENERGY FROM PIGMENT TO PIGMENT IN THE PHOTOSYSTEM UNTIL IT REACHES A REACTION CENTRE (chlorophyll a)

AN ELECTRON IS THEN ‘KICKED’ TO A HIGHER E-LEVELREDOX REACTIONS THEN MOVE THE ELECTRON TO A “PRIMARY ELECTRON ACCEPTOR” CALLED PLASTOQUINONE or PQ

I.O.U. CONCEPT !!!!!

THERE ARE 2 PHOTOSYSTEMS:

PI or P700ACTIVATED BY A PHOTON OF 700nm

PII or P680680nm PHOTON ACTIVATES IT

LIGHT HAS MUTLIPLE ENTRANCE PTS

SYSTEM MUST ALSO BE ‘RELOADED’

ENERGY HAS BEEN TRANSFERRED FROM SOLAR OR RADIANT ENERGY (light) INTO CHEMICAL POTENTIAL ENERGY (PQ)

JUST AS IN THE ETC IN RESPIRATION THE ELECTRONS ARE THEN MOVED FROM ONE PROTEIN TO ANOTHER ALONG THE MEMBRANE

(PQ CYTOCHROME COMPLEXES PLASTOCYANIN Pc P700 FERREDOXIN Fd)

THIS CAUSES H+ TO BE PUMPED INTO THE LUMEN

EVENTUALLY THE ELECTRONS REACH NADPH REDUCTASE – WHICH ATTACHES THE ELECTRONS AND SOME H+ TO NADP+ CREATING NADPH

H+ THAT BUILDS UP IN THE LUMEN CREATE AN ELECTROCHEMICAL GRADIENT.

AS THIS EQUALIZES THE H+ PASS THROUGH ATP Synthase AND CATALYZE ADP + Pi ATP

“Z DIAGRAM”

A

B

“Z DIAGRAM”

A – NON-CYCLIC e- FLOWA Z-PROTEIN SPLITS H20 AND THE ELECTRONS THEN REPLENISH THOSE LOST BY P680 (PHOTOSYSTEM II) AND OXYGEN IS CREATED AS WASTE

CALLED NON-CYCLIC BECAUSE THE ORIGINAL ELECTRONS ARE NOT RETURNED TO P680

B – CYCLIC ELECTRON FLOWSOME LIGHT WILL ONLY ACTIVATE PHOTOSYSTEM I (P700)

THE ELECTRON IS DOES NOT GET USED TO MAKE NADPH BUT IT DOES HELP SYNTHESIZE ATP

INSTEAD IT IS RETURNED TO REPLENISH PHOTOSYSTEM I (P700)

PHOTOSYNTHESIS OVERVIEW

DARK REACTIONS/CALVIN CYCLE

OCCURS IN THE STROMA

CYCLIC PROCESS INVOLVED IN CARBON FIXATION ABSORBING C02 FROM THE AIR AND ATTACHING IT TO ORGANIC MOLECULES

OCCURS IN 3 PHASES:

1.CARBON FIXATION

2.REDUCTION

3.REGENERATION OF RuBP

CARBON FIXATIONCO2 COMES INTO THE STROMA FROM THE LEAVES

3CO2 BINDS TO 5 EXISTING RuBP (5C) TO FORMS 3 UNSTABLE 6C MOLECULE AND EACH SPLITS INTO TWO 3-PG’S (3C)3CO2 + 3 x RuBP (5C) 3 x 2 3-PG (3C)

RuBP3-PG

THE ENZYME RUBISCO CATALYZES THE FIXATION OF ATMOSPHERIC CO2 INTO THE TWO 3-PG MOLECULES

IT WORKS VERY SLOWLY AND MANY COPIES ARE NEEDED TO MAKE THE PROCESS POSSIBLE

RUBISCO MAY ACCOUNT FOR UP TO ½ THE PROTEIN IN A LEAF EXTREMELY ABUNDANT

C-FIXATION

RUBSICO

REDUCTION

REGENERATION

REDUCTION

ATP DONATES A P TO EACH 3-PG

3-PG BECOMES 1,3-BPG

1,3-BPG IS THEN REDUCED BY NADPH LOSES THE P AND GAINS A H+ TO BECOME

G3P

STARTED WITH 6 3-PG’s 6 G3P’s

5 GO ON TO REGENERATE … 1 GOES ON TO BECOME PART OF GLUCOSE

C-FIXATION

RUBSICO

REDUCTION

REGENERATION

REGENERATION OF RuBP

G3P THEN GETS A P FROM ATP TO PRODUCE RuBP WHICH REACTIVATES THE CALVIN CYCLE

SIMILAR IDEA TO THE KREB’s CYCLE AND REGENERATING OXALOACETATE

C-FIXATION

RUBSICO

REDUCTION

REGENERATION

FATE OF G3PMADE INTO GLUCOSE BY A SERIES OF ENZYMES

GLUCOSE CAN THEN BE CONVERTED TO:

CELLULOSE (CELL WALLS)

STARCH (STORAGE)

USED IN CELL RESPIRATION

NOT ALL PLANTS DO THE CALVIN CYCLE THE SAME WAY RUBISCO ISN’T AS EFFECTIVE AT HIGHER TEMPERATURES… LEAVES BUILT TO REDUCE H20 LOSS

SEVERAL TYPES OF PLANTS DO C4 Photosynthesis

C4 PLANTS USE A DIFFERENT ENZYME (PEP CARBOXYLASE) TO FIX C02 TO A MOLECULE CALLED PEP RESULTS IN OXALOACETATE (4C)

ORGANIC ACIDS ARE THEN MOVED INTO THE C3 PATHWAY

IN PLANTS WHERE H20 LOSS IS A SERIOUS PROBLEM (DESERT PLANTS) CAM PHOTOSYNTHESIS OCCURS

LEAVES OPEN AT NIGHT AND STORE C02, DO C-FIXATION AND THEN STORE THE C4 PRODUCTS TO BE USED DURING THE DAY IN THE CALVIN CYCLE (C3)

THE END