Bioenergetics

Bioenergetics : the quantitative study of energy transductions in living cells and the physical-chemical nature underlying these processes.

Cells need energy to do all their work To generate and maintain its highly ordered structure (biosynthesis of macromolecules). To generate motion (mechanical work). To generate concentration and electrical gradients across cell membranes (active transport). To generate heat and light. The “ energy industry ” (production, storage and use) is central to the economy of the cell society!

Cells have to use chemical energy to do all their work Living cells are generally held at constant temperature and pressure: chemical energy (free energy,  G ) has to be used by living organisms. Biological energy transformation obey the two basic laws of thermodynamics. The free energy concept of thermodynamic is more important to biochemists than to chemists

Summary Bioenergy is chemical energy, studied in terms of free energy and free energy change (  G ). ATP acts as the free energy carrier (currency) in cells. Bioenergy is mainly produced via stepwise electron flow (redox reactions) through a series of electron carriers having increasing levels of reduction potential ( E ). Electrons released from the oxidation of nutrient fuels are initially channeled to a few universal electron carriers (including NADH and FADH 2 ).

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

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 .)

Cellular Respiration -vs- Photosynthesis

Overview of Photosynthesis 6CO 2 + 12H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O  G = + 686 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?

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

Experiment #1 H 2 18 O CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 H 2 O C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 Experiment #2 18 Oxygen (Heavy Oxygen) Isotope Experiment…

18 O Isotope Experiment 6C O 2 + 12H 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 2 + 12H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O

18 O Isotope Experiment 6C O 2 + 12H 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 2 + 12H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O

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

Tracking Atoms in Photosynthesis… 6 CO 2 12 H 2 O Reactants Products C 6 H 12 O 6 6H 2 O 6O 2

What does this suggest about photosynthesis? 6CO 2 + 12H 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 -

internal leaf structure chloroplasts outer membrane inner membrane thylakoid Plant Photosynthesis

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

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

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

Photosynthetic pigments are arranged as “photosystems”

What wavelengths of light do you think plants use the least in photosynthesis?

Photosystems use some wavelengths of light but reflect others…

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

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

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

Bioenergetics

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