PHOTOSYNTHESIS: OVERALL REACTIONPHOTOSYNTHESIS: OVERALL REACTION

6CO2 + 6H20 C6H12O6 + 6O2 Light, Chlorophyll

PHOTOSYNTHESIS: LIGHT REACTIONS VS. DARK REACTIONS

• THE FUNCTION OF THE LIGHT REACTIONS IS TO CONVERT SUNLIGHT INTO CHEMICAL ENERGY (ATP AND NADPH).

• THE DARK REACTIONS FIX CO2 INTO SUGARS, USING THE ATP AND NADPH GENERATED BY THE DARK REACTIONS.

LIGHT HAS CHARACTERISTICS OF BOTH A PARTICLE AND A WAVE

A WAVE IS CHARACTERIZED BY A WAVELENGTH AND A FREQUENCY

c =

LIGHT IS ALSO A PARTICLE WHICH WE LIGHT IS ALSO A PARTICLE WHICH WE CALL A PHOTONCALL A PHOTON

EACH PHOTON CONTAINS AN AMOUNT OF ENERGY CALLED A QUANTUM.

THE ENERGY CONTENT OF LIGHT IS NOT CONTINUOUS, BUT IS DELIVERED IN DISCREET PACKETS OR QUANTA.

E = h, where h is Planck’s constant

Bacteriochlorophyll aChlorophyll a Phycoerythrobilin

-carotene

Chlorophyll b

ENGELMANN EXPERIMENT (1881)ENGELMANN EXPERIMENT (1881)

PHOTOSYNTHESIS TAKES PLACE IN PHOTOSYNTHESIS TAKES PLACE IN

COMPLEXES CONTAINING LIGHT-COMPLEXES CONTAINING LIGHT-

HARVESTING ANTENNAS AND HARVESTING ANTENNAS AND

PHOTOCHEMICAL REACTION CENTERSPHOTOCHEMICAL REACTION CENTERS

EMERSON AND ARNOLD’S FLASHING LIGHT EXPERIMENTS WITH CHLORELLA (1932)

1. Gave brief flashes (10-5 s) of light to Chlorella suspension and measured the amount of O2 produced. (The flashes were spaced 0.1 s apart for maximum efficiency of dark reaction.)

2. Varied intensity (light energy) of flash and plotted the O2 produced per flash versus the flash energy (number of photons).

QUANTUM YIELD = 0.1

RED DROP EFFECT

Carotenoid absorption: carotenoids have photoprotective effect

EMERSON ENHANCEMENT EFFECT

Stroma lamellae

Double membrane

Grana stack (thylakoids)

Stroma

PSII

PSI

PSI

Antenna complex as energy funnel

LHCII Antenna Complex

~15

LHCII PROTEIN

PSI

CHEMIOSMOTIC MECHANISM