Biochemistry of Photosynthesis An introduction…

Photosynthesis – What can you remember? What is the word equation for photosynthesis? What is the balanced symbol equation for photosynthesis? Where do all of the raw materials come from and what happens to the products

Photosynthesis

Energy Transfers & Photosynthesis __________ energy (from sunlight) __________ energy (glucose) respiration _________ energy in glucose is transferred to another molecule ________ Light Chemical potential ATP

What provides the energy within cells? ATP…Adenosine Tri Phosphate Common to ALL living things Chemical energy is stored in the phosphate bonds 3 phosphates Ribose sugar Adenine base

What Does ATP Do for You? It supplies YOU with ENERGY! Copyright Cmassengale

How Do We Get Energy From ATP? Hydrolysis reaction - breaking the high- energy bonds between the last two phosphates in ATP Copyright Cmassengale

How does ATP provide the energy? Chemical energy is stored in the phosphate bonds, particularly the last one To release the energy, a HYDROLYSIS reaction takes place to break the bond between the last two phosphate molecules Catalysed by ATP-ase ATP is broken down into ADP and P i For each mole of ATP hydrolysed, about 34kJ of energy is released Some is lost, but the rest is useful and is used in cell reactions

Synthesising ATP ADP + Pi + energy ATP ATP is created via respiration in both animals and plants

Where does the energy to synthesise ATP come from? Catabolic (breakdown) reactions Redox (reduction/oxidation) reactions Reduction The main way in which ATP is synthesised is by the removal of hydrogen atoms from intermediate compounds in a metabolic pathway We say the hydrogen carrier is reduced Electrons from the hydrogen atoms are passed along carriers (Electron Transfer Chain) When a component of the chain receives one of the hydrogen atoms, we say it is REDUCED When a component passes an electron on, we say it is OXIDISED Each of these redox reactions releases a small amount of energy and this energy is used to synthesise ATP

Phosphorylation

What does this have to do with photosynthesis? ATP is both synthesised and broken down during photosynthesis! 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 Light energy is required Chlorophyll Stored within chloroplasts chloroplasts per plant cell

Why is Photosynthesis important? Only by photosynthesis that light energy is converted into chemical potential energy and simple in organic molecules eg CO 2 and H 2 O can be built up into organic ones. Ultimately all animals rely on photosynthesis

Where in plant cells does photosynthesis happen?

Structure of the chloroplast Label you diagram to show the structure of the chloroplast: Granum Outer membrane Inner membrane Stroma Thylakoids

Where in the plant cell does photosynthesis take place?

The membranes from the grana provide a large surface area for chlorophyll molecules and other light absorbing pigments The pigments form clusters called photosystems. Photosystems act as light-collecting systems. Light is captured and passed from one pigment molecule to another before it finally reaches a chlorophyll molecule

Photosynthesis involves lots of separate reactions 2 basic steps: Light-dependant reactions Light independent reactions

The light dependant reaction Learning objectives: Explain the role of photosystems in the light dependant reactions Describe the light-dependant reactions to explain how sunlight is used to synthesise ATP and reduced NADP

Photosystems Pigments arranged in funnel shaped photosystems that sit in the thylakoid membrane Each photosystem = hundreds of pigment molecules Various pigments absorb light of different wavelengths and pass the energy down the photosystem.

Photosystems 2 types: –Photosystem 1 –Photosystem 2 Each photosystem is sensitive to light if different wavelengths

Step 1 – Photolysis Water 2H + + 2e - + 1/2 O2 The electrons pass to photosystem 1 Water is broken down to protons, electrons and oxygen 2e- PS 2

Step 2 – Light energy excites electrons in chlorophyll Light strikes chlorophyll molecule in photosystem II Energy levels of 2 electrons are raised. The electrons leave the chlorophyll molecule 2e- PS 2 Light energy 2e-

Step 2– Energy from these excited electrons generate ATP Electrons are passed to electron carrier Electrons passed along series of electron acceptors which form an electron transfer chain in chloroplast membrane 2e- PS 2 Light energy 2e- Electron Carrier

Step 2– Energy from these excited electrons generate ATP 2e- PS 2 Light energy 2e- Electron Carrier ADP+ Pi ATP e- loose energy as they pass along. This energy is used to generate ATP

Step 3– Light also strikes PS1 2e- PS 2 Light energy 2e- Electron Carrier ADP+ Pi ATP 2e- PS 1 Light energy 2e- Light strikes chlorophyll molecule in photosystem I Electron Carrier

Step 3– Light also strikes PS1 2e- PS 2 Light energy 2e- Electron Carrier ADP+ Pi ATP 2e- PS 1 Light energy 2e- Electron Carrier Electrons pass down another series of electron carriers.

Step 3– Energy from these excited electrons generate NADP 2e- PS 2 Light energy 2e- Electron Carrier ADP+ Pi ATP 2e- PS 1 Light energy 2e- Electron Carrier NADP + 2H + 2e - The e - are used with the H + (produced from photolysis of H 2 O) to produce reduced NADP

NADP NADP Nicotinamide Adenine dinucleotide phosphate Coenzyme found in plant cells Aids electron transfer during photosynthesis

The light dependant reaction In the light dependant reactions of photosynthesis what happens to the electrons that come from: a.A water molecule b.A chlorophyll molecule in photosystem I c.A chlorophyll molecule in photosystem II hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/fre e/ /120072/bio13.swf::Photosynthetic%20Electron %20Transport%20and%20ATP%20Synthesis

The Light Dependant reaction 1.Where in the chloroplast do these take place? 2.What are the 2 main products of the light dependant reactions? 3.What waste product is made during the light dependant reactions?

Light-independent reactions –The Calvin Cycle Take place in the liquid stroma Makes hexose sugars eg glucose from carbon dioxide and RuBP (riboulose bisphosphate)

Light-independent reactions –The Calvin Cycle Needs energy and H+ Provided by products of light dependant reaction – ATP and reduced NADP

The Calvin Cycle CO 2 RuBisCO 1C 6C Ribulose bisphosphate 5C CO2 enters the leaf through the stomata & diffuses into the stroma of the chloroplast CO 2 reacts with ribulose bisphosphate (5-C) The reaction is catalysed by the enzyme RuBisCO This produces an unstable 6-C compound which quickly breaks down

The Calvin Cycle CO 2 RuBisCO 1C 6C Ribulose bisphosphate 5C 2x Glycerate 3-phosphate 3C 2 molecules of Glycerate 3 – phosphate are formed Energy from ATP and hydrogen from reduced NADP is used to convert each glycerate 3- phosphate into triose phosphate ATP ADP + Pi Reduced NADP NADP 3C Triose Phosphate

The Calvin Cycle CO 2 RuBisCO 1C 6C Ribulose bisphosphate 5C 2x Glycerate 3-phosphate 3C 2 molecules of Glycerate 3 – phosphate are formed Energy from ATP and hydrogen from reduced NADP is used to convert each glycerate 3- phosphate into triose phosphate ATP ADP + Pi Reduced NADP NADP 3C Triose Phosphate

The Calvin Cycle CO 2 RuBisCO 1C 6C Ribulose bisphosphate 5C 2x Glycerate 3-phosphate 3C Most of the triose phosphate is used to make more ribulose bisphospate ATP ADP + Pi Reduced NADP NADP 3C Triose Phosphate ATP ADP + Pi

The Calvin Cycle Some is used to form carbohydrates CO 2 RuBisCO 1C 6C Ribulose bisphosphate 5C 2x Glycerate 3-phosphate 3C ATP ADP + Pi Reduced NADP NADP 3C Triose Phosphate 1C

The Calvin cycle needs to turn 6 times to make 1 glucose molecule 6CO2 (1C ) 6RuBP (5C ) 12 glycerate 3-phosphate (3C ) 12 triose phosphate (3C ) 10 triose phosphate (3C ) 6 RuBP(5C ) 2 triose phosphates (3C ) 1 glucose (3C )