Energy Generation in Mitochondria and Chloroplasts Chapter 14 Energy Generation in Mitochondria and Chloroplasts

Generation of Energy Millions of years ago there was no O2 available for oxidative phosphorylation to occur Organisms produced energy from fermentation, still see this today As O2 became available, a more efficient method of energy production developed Based on the transfer of e- along the membrane

Organism’s Energy Source Small amount of ATP from glycolysis in the cytosol of cells Majority made by a membrane based process in 2 stages Stage 1 – e- transport chain e- transferred along e- carriers in the membrane Stage 2 – flow of H+ down an electrochemical gradient to produce ATP Use a complex called ATP synthase

Stage 1 NADH (from the Kreb’s cycle) brings in the e- and transfers them to the carrier molecules The e- moves down the chain and looses energy at each step – as this happens, H+ are pumped across the membrane This creates an electro-chemical gradient across the membrane

Stage 2 The electrochemical gradient is a form of stored energy – it has the potential to do work The H+ can now move down the gradient and return to the other side of the membrane thru ATP synthase – in this process, generates ATP from ADP and Pi

Chemiosmotic Coupling Once called the chemiosmotic hypothesis Chemi from making ATP, osmotic because of crossing the membrane Now known as chemiosmotic coupling

Mitochondria Produce most of a cells ATP – acetyl groups in the Kreb’s cycle producing CO2 and NADH NADH donates the e- to the electron transport chain and becomes oxidized to NAD+ e- transfer promotes proton pump and ATP synthesis in process called oxidative phosphorylation Cells that require large amounts of energy such as the heart have large numbers of mitochondria

Mitochondria Contain their own copies of DNA and RNA along with transcription and translation system (ribosomes) Are able to regenerate themselves without the whole cell undergoing division Shape and size dependent on what the cell’s function is

Mitochondria Double membrane creates 2 spaces Matrix: large internal space Intermembrane space: between the membranes Outer membrane Inner membrane

Mitochondria

Inner Membrane Inner membrane is the site of the e- transport chain, across which the proton pump occurs and contains ATP synthase Inner membrane is highly folded – called cristae – increasing the surface area on which the above reactions can take place

High Energy e- Mitochondria use pyruvate and fatty acids and convert it to acetyl CoA in the matrix Citric acid cycle generates NADH and FADH2 which carry the e- to the electron transport chain

Summary – MUST KNOW

Proton Pumping Many molecules can supply the e- - carbohydrates and fatty acids O2 ultimate e- acceptor producing H2O as waste

Movement of Electrons

Oxidative Phosphorylation

Electron Transport Chain Resides in the inner mitochondrial membrane – also called respiratory chain 15 proteins involved in the chain – grouped in 3 large respiratory enzyme complexes NADH dehydrogenase complex Cytochrome b-c1 complex Cytochrome oxidase complex Pumps protons across the membrane as e- are transferred thru them

Respiratory Enzyme Complexes

Proton Gradient e- transfer is an oxidation/reduction reaction NADH has high-energy e- has a low electron affinity so the e- is readily passed to NADH dehydrogenase and so on down the chain Each transfer couples the energy released with the uptake of a H+ from the matrix to the intermembrane space setting up the electrochemical gradient

Proton Gradient Gradient of proton (H+) concentration across the inner mitochondrial membrane – a pH gradient with the pH in the matrix higher than in the intermembrane space Proton pumping also generates a membrane potential – matrix side is negative and intermembrane space is positive

4 Complexes in Membrane

Location of H+

Electrochemical Gradient

Oxidative Phosphorylation ATP synthase is the protein complex responsible for making ATP by creating a path for H+ thru the membrane ATP synthase is an enzyme

ATP Synthase Multisubunit protein responsible for making ATP

Summary

Bidirectional Pump

Coupled Transport Can Move Other Molecules

Oxidation of Sugar and Fats