Energy Generation in Chloroplasts Chapter 13 & 14 Energy Generation in Chloroplasts

Chloroplasts and Photosynthesis Photosynthesis is process using the energy in sunlight and CO2 to create the organic materials required of present day cells The chloroplast is the special organelle in plants responsible for photosynthesis

Chloroplasts Similar to mitochondria Uses a proton pump to create ATP Stroma instead of matrix Has own RNA, DNA and ribosomes Difference is that the e- transport chain is in the thylakoid membrane – 3rd membrane that makes up the thylakoids, a sac-like structure, so have a thylakoid space Granum – stack of thylakoids Chloroplasts

Chloroplasts vs Mitochondria

Light and Dark Reactions Light or photosynthetic e- transfer reactions Sunlight energizes e- in chlorophyll which then moves down the e- transport chain in the thylakoid membrane e- gotten from H2O to make O2 Electrochemical gradient is made in the stroma across the thylakoid membrane making ATP Generate NADPH from NADP+ Dark or carbon-fixation reactions ATP and NADPH produced in light reaction used as energy and reducing power to take CO2 and convert it to a carbohydrate – sucrose

Photosynthesis Reactions

Chlorophyll Sunlight is composed of many different wavelengths ranging from violet to red Chlorophyll is green because it absorbs all the wavelengths but green The e- in chlorophyll gain a higher energy level when a wavelength is absorbed and then bounce around the ring – porphyrin (blue)

Photosystem Chlorophylls are in a multiprotein complex called a photosystem Antenna is many molecules of chlorophyll that capture the sunlight’s energy that ultimately goes to the reaction center

Reaction Center Set of proteins in the thylakoid membrane Special chlorophyll molecule that is an irreversible trap for an excited e- Transfers the e- to a more stable environment

ATP and NADPH The light reaction makes the ATP and NADPH (reducing power) to synthesize the sugar ATP made with the first photon of light absorbed and NADPH is made from the second photon of light

Summary of Light Reactions Electron from chlorophyll in photsystem II is donated to NADPH The replacement electron comes from the splitting of water When 4 electrons are removed (4 photons hit chlorophyll) O2 is released

Carbon Fixation

Carbon-Fixation or Calvin Cycle CO2 joins with a ribulose 1,5-bisphosphate (5 C) by a carboxylase called rubisco Rubisco is slow compared to other enzymes so therefore there is a large amount in the cell to compensate for this 1 molecule of glyceraldehyde 3-phosphate (net product ) is generated and goes to make the sugar A large amount of energy goes to regenerating the ribulose 1,5-bisphosphate 3 ATP and 2 NADPH required for each CO2 molecule converted to carbohydrate

Glyceraldehyde 3-phosphate Converted into sucrose Can be shuttled into the glycolytic pathway in the mitochondria of plants to become pyruvate and eventually ATP Excess is converted into starch in the stroma which can be used at night as an energy source