Supramolecular Chemistry, UAF, 2005 Photosynthesis

Photosynthesis Where does the energy come from that sustains all life? The Sun!! Well most of it anyway……

Supramolecular Chemistry, UAF, 2005 Respiration vs. Photosynthesis Photosynthesis and respiration as complementary processes in the living world. Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food. Respiration is a process that uses O 2 and forms CO 2 from the same carbon atoms that had been taken up as CO 2 and converted into sugars by photosynthesis. In respiration, organisms obtain the energy that they need to survive. Photosynthesis preceded respiration on the earth for probably billions of years before enough O 2 was released to create an atmosphere rich in oxygen. (The earth's atmosphere presently contains 20% O 2.)

Supramolecular Chemistry, UAF, 2005 Cellular Respiration -vs- Photosynthesis

Supramolecular Chemistry, UAF, 2005 Overview of Photosynthesis 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O  G = kcal/mol Photosynthesis, like cellular respiration, is a series of redox reactions! What is being oxidized and what is being reduced in the summarizing equation above?

Supramolecular Chemistry, UAF, 2005 Early thinking: O 2 released came from the CO 2 CO 2  C + O 2 C + H 2 O  CH 2 O sugar Water was added to the carbon to make sugar van Neil’s experiments with the sulfur bacteria showed that the bacteria used CO 2 but did NOT release O 2...he suggested that plants split water as a source of e - and H + Historical perspective Scientists used radioactive isotopes to test this idea

Supramolecular Chemistry, UAF, 2005 Experiment #1 H 2 18 O CO 2 H2OH2O C 18 O 2 Experiment #2 18 Oxygen (Heavy Oxygen) Isotope Experiment…

Supramolecular Chemistry, UAF, O Isotope Experiment 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 Hypothesis: If CO 2 is being oxidized H 2 18 O 18 O Can you predict where the heavy oxygen will end up in each case? 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O

Supramolecular Chemistry, UAF, CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 Hypothesis: If H 2 O is being oxidized H 2 18 O 18 O Can you predict where the heavy oxygen will end up in each case? 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O 18 O Isotope Experiment

Supramolecular Chemistry, UAF, CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 H 2 18 O 18 O 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O The Actual Results!! So..it’s the water that’s being oxidized!

Supramolecular Chemistry, UAF, CO 2 12 H 2 OReactants Products C 6 H 12 O 6 6H 2 O 6O 2 Tracking Atoms in Photosynthesis…

Supramolecular Chemistry, UAF, 2005 What does this suggest about photosynthesis? 6CO H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO 2 and adding water! oxidized reduced H + and e -

Supramolecular Chemistry, UAF, 2005 internal leaf structure chloroplasts outer membrane inner membrane thylakoid Plant Photosynthesis

Supramolecular Chemistry, UAF, 2005 The stages of photosynthesis… Light Dependent Reactions Occurs along the thylakoid membrane this is where H 2 O is oxidized. chemiosmotic production of ATP! electron carrier (NADPH) is synthesized

Supramolecular Chemistry, UAF, 2005 Light Independent Reactions Occurs in the stroma of the chloroplast. Where CO 2 is “fixed” into sugars! The stages of photosynthesis…

Supramolecular Chemistry, UAF, 2005 How plants harness energy from sunlight… Photosynthetic pigments Chlorophylls a – the “main” photosynthetic pigment Chlorophyll b Accessory pigments.. Carotenoids

Supramolecular Chemistry, UAF, 2005 Photosynthetic pigments are arranged as “photosystems”

Supramolecular Chemistry, UAF, 2005 What wavelengths of light do you think plants use the least in photosynthesis?

Supramolecular Chemistry, UAF, 2005 Photosystems use some wavelengths of light but reflect others…

Supramolecular Chemistry, UAF, 2005 Light Harvesting Pigments Reaction Center Photon Photosystem From the Photosystem, e - are passed along an Electron Transport Chain.. The Photosynthetic Electron Transport Chain (PETC)

Supramolecular Chemistry, UAF, 2005 PETC Photon Photosystem

Supramolecular Chemistry, UAF, 2005 Photosynthetic Electron Transfer Chain (PETC) series of electron carriers which take electrons from photosystem, and.. ultimately carry electrons to NADP +

Supramolecular Chemistry, UAF, 2005 Photosystems Experiments in the 1940’s suggested that light photons are absorbed at 2 different points along the same PETC.… In fact, there are two Photosystems in operation

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