Wednesday, 30 May 2018 3.5 Energy transfer in and between organisms 3.5.2 Respiration – Oxidative Phosphorylation • explain the process of electron transfer associated with oxidative phosphorylation • explain chemiosmosis and the role of ATP synthase in producing ATP • apply knowledge to explain trends in data.

Oxidative Phosphorylation Is the process where the energy carried by electrons, from reduced coenzymes (reduced NAD and FAD by oxidising them) is to make ATP It uses the Electron transport chain (chain of proteins where excited electrons travel) and chemiosmosis (electrons flowing down the electron transport chain and creating a proton gradient across a membrane to drive ATP synthesis)

Respiration The process of aerobic respiration can be split into 4 stages: Glycolysis (splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules) Link reaction (the 3-carbon pyruvate molecules enter a series of reactions which lead to acetylcoenzyme A – a 2-carbon molecule) Krebs Cycle (acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD Oxidative phosphorylation (electrons from NAD and FAD are released from the Krebs cycle to synthesis ATP with water produced as a by-product

Complete the Table ATP Carbon Dioxide Reduced NAD Reduced FAD How many of each one is produced during the following stages of Aerobic Respiration? GLYCOLYSIS LINK REACTION KREBS CYCLE 2x ATP, zero carbon dioxide, 2x reduced NAD, zero reduced FAD zero ATP, 2x carbon dioxide, 2x reduced NAD, zero reduced FAD 2x ATP, 4x carbon dioxide, 6x reduced NAD, 2x reduced FAD Glycolysis = 2x ATP, zero carbon dioxide, 2x reduced NAD, zero reduced FAD Link Reaction = zero ATP, 2x carbon dioxide, 2x reduced NAD, zero reduced FAD Krebs cycle = 2x ATP, 4x carbon dioxide, 6x reduced NAD, 2x reduced FAD

So where does the rest of the energy come from? Where does the remaining 28 ATP come from? The Electron Transport Chain! The ETC makes ATP from the reduced NAD and Reduced FAD made in the earlier stages. Each reduced FAD will generate 1.5ATP Each reduced NAD will generate 2.5ATP

Where they come from and how many? Reduced FAD 2 (from Krebs) 1.5 X 2 = 3 ATP (ETC) Reduced NAD 2 (from Glycolysis) 2 (from 2x link reaction) 6 (from 2x Krebs) 2.5 X 10 = 25 ATP (ETC) 3 ATP + 25 ATP = 28 ATP Add this to the 4 ATP made directly in glycolysis and krebs and you have 32 ATP altogether!

What Happens Where? Glycolysis = Cytoplasm of the cell. Link reaction = Matrix of the mitochondria. Krebs cycle = Also in the matrix. Electron transport chain Utilises proteins found in the membrane of the cristae. Discuss adaptations of mitochondria and metabolically active cells e.g. Muscle cells

Oxidative Phosphorylation

Oxidative phosphorylation is the terminal process of cellular respiration. During oxidative phosphorylation electrons are transferred from NADH or FADH2, to molecular oxygen via a series of protein complexes located in the inner mitochondrial membrane. Protons are pumped from the mitochondrial matrix into the intermembrane space as a result of this flow of electrons

Electron Transport Chain The ETC is a series of hydrogen and electron carriers (proteins) located on the membranes of the cristae 2H atoms are ionised into 2H+ and 2e- Electrons (e-)are passed from one carrier to the next – losing energy as they go

Electron Transport Chain The energy released in this stepwise process is used to produce ATP Oxygen is the final electron acceptor and is reduced to water The formation of ATP, via the electron transport chain in a mitochondrion is called oxidative phosphorylation

The Fate of the hydrogens –The Electron transport chain. ETC and Chemiosmosis Summary The Fate of the hydrogens –The Electron transport chain. Chemiosmosis Theory STUDENT HANDOUT This method of ATP production is termed Oxidative Phosphorylation

Electron Transport Chain THE MOVIE! http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

Electron Transport Chain http://highered.mcgraw-hill.com/olc/dl/120071/bio11.swf http://www.science.smith.edu/departments/Biology/Bio231/etc.html http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20transport.swf

Why is the theoretical maximum yield of ATP per glucose molecule rarely achieved? Some protons leak across the mitochondrial membrane, reducing the number of protons to flow through the ion channels and generate ATP Some ATP produced is used to actively transport pyruvate into the mitochondria Some ATP is used for the shuttle to bring hydrogen from reduced NAD made during glycolysis, in the cytoplasm, into the mitochondria

The energy released from hydrolysis of ATP

Coenzyme A

Nicotinamide adenine dinucleotide (NAD)

FAD

http://highered. mheducation http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_atp_synthesis__quiz_1_.html http://www.bozemanscience.com/cellular-respiration/?rq=respiration Respiration Song

Respiratory substrate A respiratory substrate is an organic substance that can be used for respiration

Respiratory substrate Mean energy value/kJg-1 Difference in relative energy values of carbohydrate, lipid and protein The more hydrogen there are in a molecule of respiratory substrate, the more ATP can be generated when that substrate is respired Respiratory substrate Mean energy value/kJg-1 Carbohydrate 15.8 Lipid 39.4 Protein 17.0

Difference in relative energy values of carbohydrate, lipid and protein Carbohydrates Animals store glucose as glycogen and plants store it as starch Both can be hydrolysed to glucose for respiration Fructose and galactose are changed to glucose for respiration

Difference in relative energy values of carbohydrate, lipid and protein During starvation or prolonged exercise, protein from muscle can be hydrolysed to amino acids which can be respired Some can be converted to pyruvate, or to acetate, which can be respired via the Krebs Cycle Some can enter Krebs Cycle directly

Difference in relative energy values of carbohydrate, lipid and protein Lipids Glycerol can be converted to glucose, and then respired Fatty acids are long-chain hydrocarbons. There are therefore many hydrogen atoms as a source of protons for oxidative phosphorylation The fatty acids are broken down to 2 carbon acetyl groups and enter the Krebs cycle

Questions! Explain why palmitic acid, a large molecule, can pass into the matrix of the mitochondria Why can fats and proteins only be respired aerobically? Explain why children whose diet does not contain enough fat or carbohydrate can suffer from muscle wastage

Answers! It is a fat so dissolves in the lipid bilayer of the mitochondrial membranes Fats and proteins are respired via the Krebs Cycle They will use muscle protein as a source of amino acids for respiration

IN DETAIL - Oxidative Phosphorylation produces lots of ATP Hydrogen atoms are released from NADH + H+ and FADH2 (as they are oxidised to NAD+ and FAD). The H atoms split to produce protons (H+) and electrons (e-) for the chain. The electrons move along the electron chain (made up of three electron carriers) losing energy at each level. This energy is used to pump the protons (H+) into the space between the inner and outer mitochondrial membranes (the intermembrane space)

Oxidative Phosphorylation produces lots of ATP The concentration of protons is higher in the intermembrane space than in the mitochondrial matrix, so an electrochemical gradient exists. The protons then move back through the inner membrane down the electrochemical gradient, through specific channels on the stalked particles of the cristae- this drives the enzyme ATP synthase. By spinning like a motor, this enzyme supplies electrical potential energy to make ATP from ADP and inorganic phosphate The protons and electrons recombine to form hydrogen, and this combines with molecular oxygen (from the blood) at the end of the transport chain to form water. Oxygen is said to be the final electron acceptor