The conversion of light energy into organic molecules PHOTOSYNTHESIS The conversion of light energy into organic molecules

Energy needs of life All life needs a constant input of energy (food) Heterotrophs (Animals) eat food = other organisms = organic molecules Autotrophs (Green Plants) convert energy of sunlight into organic molecules (CHO) from CO2 make energy & synthesize sugars through photosynthesis There is also Chemosynthesis (bacteria make orgasnic molecules using chemical energy) Both use Respiration to convert energy of organic molecules (food) into ATP consumers Producers

History 1665 Do plants “eat” soil? After 5 years the willow twig gained 164 lbs., but the soil only lost 2 oz. Water and air make more plant matter Von Helmont

Plants keep animals alive Plants “restore” bad air Joseph Priestley 1771

Wavelength’s of light Why? Engelmann – more oxygen is released with red and blue light Photosynthesis is better in red and blue light than in green light Why?

+ water + energy  glucose + oxygen Equation + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + What do you notice about this equation? It’s the reverse of respiration (although the individual parts of the reaction are not)

+ water + energy  glucose + oxygen Equation + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + CO2 is reduced to C6H12O6 (Reduction requires an input of energy)

Chloroplasts “Dark Reaction” Contain chlorophyll “Light Reaction”

chloroplasts in plant cell chloroplasts contain chlorophyll absorb sunlight & CO2 cross section of leaf leaves CO2 chloroplasts in plant cell chloroplasts contain chlorophyll chloroplast make energy & sugar

Plant structure Chloroplasts Thylakoid membrane contains double membrane stroma fluid-filled interior thylakoid sacs grana stacks Thylakoid membrane contains chlorophyll molecules electron transport chain ATP synthase H+ gradient built up within thylakoid sac ATP outer membrane inner membrane granum stroma thylakoid A typical mesophyll cell has 30-40 chloroplasts, each about 2-4 microns by 4-7 microns long. Each chloroplast has two membranes around a central aqueous space, the stroma. In the stroma are membranous sacs, the thylakoids. These have an internal aqueous space, the thylakoid lumen or thylakoid space. Thylakoids may be stacked into columns called grana.

Chlorophyll Chlorophyll a (C55H72O5N4Mg) – major photosynthetic pigment. It is blue-green. Chlorophyll b (C55H70O6N4Mg – is one of the accessory pigments. It is yellow-green. “head” Fatty “tail”

Absorption and Action Spectra Blue and orange-red are absorbed best by Chl.a More photosynthesis can occur with green-yellow because Accessory pigments can pass energy to Chl. a

Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a absorbs best in red & blue wavelengths & least in green accessory pigments with different structures absorb light of different wavelengths – pass energy to Chl. a chlorophyll b, carotenoids (carotene), xanthophylls

Experimental evidence Where did the O2 come from? isotope tracer = O18 6CO2 6H2O C6H12O6 6O2 light energy  + Experiment 1 6CO2 6H2O C6H12O6 6O2 light energy  + 6CO2 6H2O C6H12O6 6O2 light energy  + Experiment 2 Proved O2 came from H2O not CO2 = plants split H2O!

We need a new equation 6CO2+ 6H2O* C6H12O6 + 6 O2* What is wrong with that equation? It’s not balanced More accurate equation 6CO2 + 12H2O* C6H12O6 + 6O2* + 6H2O Plants use more water and they also produce water.

Light and Dark Reactions Photosynthesis has two reactions which occur at the same time The Light Dependent Reaction (Light) which uses light The Light Independent Reaction (dark) which does not use li ght

It’s not the Dark Reactions! Light reactions light-dependent reactions energy conversion reactions convert solar energy to chemical energy ATP & NADPH light-independent reactions Calvin Cycle sugar building reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 It’s not the Dark Reactions!

Summary The Light Dependent reactions Light energy is trapped by Chl.a (Photosystems I and II) and H2O is split. O2 is released and ATP and NADPH are produced The Light Independent reactions The Calvin Cycle uses the ATP and NADPH to reduce CO2 to Carbohydrates

Pigments of photosynthesis Chlorophylls & other pigments embedded in thylakoid membrane arranged in a “photosystem” collection of molecules

Photosystems of photosynthesis 2 photosystems in thylakoid membrane collections of chlorophyll (light-gathering) molecules Photosystem II chlorophyll a (mostly) P680 = absorbs best at 680nm Photosystem I chlorophyll b (mostly) P700 = absorbs best at 700nm reaction center Photons are absorbed by clusters of pigment molecules (antenna molecules) in the thylakoid membrane. When any antenna molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule = the reaction center. At the reaction center is a primary electron acceptor which removes an excited electron from the reaction center chlorophyll a. This starts the light reactions. Don’t compete with each other, work synergistically using different wavelengths. antenna pigments

Light Dependent Vocabulary Photophosphorylation Cyclic and non-cyclic photophosphorylation Photosystem I (P700) Photosystem II (P680) Photoionization Accessory pigments

Light Dependent Reactions Cyclic and non-Cyclic Photophosphorylation – occur simultaneously

Cylcic Photophosphorylation ETC Makes ATP only – does not reduce CO2 to sugar

Cyclic and Non-cyclic Photophosphorylation http://highered.mcgraw-hill.com/olc/dl/120072/bio12.swf

Non-Cyclic Photophosphorylation The Light Dependent reactions Use light, chlorophyll (P680 and P700), H2O, and NADP Produces O2, ATP and NADPH Uses an ETC similar to respiration to produce the ATP

ETC of Photosynthesis ETC uses light energy to produce ATP & NADPH Which go to Calvin cycle PS II and PS I absorb light excited electron passes from chlorophyll to “primary electron acceptor” enzymes extracts electrons from H2O & supply them to chlorophyll (replace the ones lost) splits H2O into ½ O and H+ O combines with another O to form O2 (released) NADP becomes NADPH

Non-cyclic Photophosphorylation

ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide generates O2

Photosystem II P680 chlorophyll a ETC of Photosynthesis thylakoid chloroplast H+ H+ ATP Plants split water 1 O H 2 e O O H e- H+ +H To NADP e e e- fill the vacancy Photosystem II P680 chlorophyll a

energy to build carbohydrates Photosystem II P680 chlorophyll a ETC of Photosynthesis thylakoid chloroplast H+ H+ ATP e H+ 3 1 2 e H+ ATP 4 to Calvin Cycle H+ ADP + Pi energy to build carbohydrates Photosystem II P680 chlorophyll a ATP

Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a ETC of Photosynthesis e e sun fill the e– vacancy e 5 Need a 2nd photon -- shot of light energy to excite electron back up to high energy state. 2nd ETC drives reduction of NADP to NADPH. Light comes in at 2 points. Produce ATP & NADPH e e Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a

ETC of Photosynthesis e e electron carrier 6 NADPH to Calvin Cycle 5 sun NADPH to Calvin Cycle Need a 2nd photon -- shot of light energy to excite electron back up to high energy state. 2nd ETC drives reduction of NADP to NADPH. Light comes in at 2 points. Produce ATP & NADPH Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a $$ in the bank… reducing power!

ETC of Photosynthesis e e O split H2O H+ sun sun to Calvin Cycle ATP Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide split H2O ATP

Photosynthesis summary Where did the energy come from? Where did the electrons come from? Where did the H2O come from? Where did the O2 come from? Where did the O2 go? Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for? Where did the energy come from? The Sun Where did the electrons come from? Chlorophyll Where did the H2O come from? The ground through the roots/xylem Where did the O2 come from? The splitting of water Where did the O2 go? Out stomates to air Where did the H+ come from? The slitting of water Where did the ATP come from? Photosystem 2: Chemiosmosis (H+ gradient) What will the ATP be used for? The work of plant life! Building sugars Where did the NADPH come from? Reduction of NADP (Photosystem 1) What will the NADPH be used for? Calvin cycle / Carbon fixation …stay tuned for the Calvin cycle