Biochemistry Arash Azarfar Lorestan University Biochemistry • Principle of energy release from food • Release of energy in the form of ATP • Glucose, fat and amino acids Lorestan University Biochemistry • Principle of energy release from food • Biological oxidation and H-transfer systems • Oxidation does not necessary involve oxygen: • May be involve in only electron removal • Ferrous/Ferric system Lorestan University Biochemistry • Principle of energy release from food • Biological oxidation and H-transfer systems • Oxidation does not necessary involve oxygen: • The removal of e- accompanied by protons from a hydrogenated molecule Lorestan University Biochemistry • Principle of energy release from food •The removal of e- accompanied by protons from a hydrogenated molecule • Electron transfers from a donor to an acceptor • Electron transferred: • Accompanied by proton • Proton may be liberated into solution Lorestan University Biochemistry • Principle of energy release from food •The ultimate electron acceptor in the aerobic cell • Oxygen Lorestan University Biochemistry • Principle of energy release from food •Oxygen is only the ultimate electron acceptor in the cell • Other electron acceptors form a chain Lorestan University Biochemistry • Principle of energy release from food •Other electron acceptors form a chain • Electron transport chain • Plays a predominant role in ATP generation Lorestan University Biochemistry Lorestan University Biochemistry • Principle of energy release from food •NAD+ (Nicotinamide adenine dinuclotide) • Involved in oxidation of many metabolites • General structure Lorestan University Biochemistry • Principle of energy release from food •NAD+ (Nicotinamide adenine dinuclotide) • Involved in oxidation of many metabolites • General structure Lorestan University Biochemistry • Principle of energy release from food •NAD+ (Nicotinamide adenine dinuclotide) • Is a coenzyme • Differs from an ordinary enzyme substrate • Reduced compound leaves the enzyme and attaches to the second enzyme Lorestan University Biochemistry •NAD+ (Nicotinamide adenine dinuclotide) • Business end Nicotinamide Lorestan University Biochemistry • Accepting 2 e- plus one proton as hydride ion (H:-) • The second proton being liberated into solution Lorestan University Biochemistry •NAD+ (Nicotinamide adenine dinuclotide) • Coenzyme for several dehydrogenases Lorestan University Biochemistry • FAD and FMN • FAD (flavin adenine dinucleotide) • Derived from Riboflavin • Important feature: • Accepting two H atoms to become FADH2 (in combination with appropriate proteins) • FAD is a prosthetic group (permanent attachment to its apoenzyme) Lorestan University Biochemistry • FAD and FMN • Structure Lorestan University Biochemistry • Energy release from glucose • Glucose or glycogen • The main stages of glucose oxidation • ΔG0´ is -2820 kJ mol-1 • Oxidation is accompanied with more than30 mol ATP Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Splitting the glucose into C3 fragments • Citric acid cycle (tricarboxylic acid, TCA; Krebs) Pyruvate C Acetyl group electron electron carriers • No oxygen is involved • Carbon atoms are released as CO2 Lorestan University Biochemistry • Oxidation of glucose: • Electron transport system • Transporting of electrons from electron carriers to oxygen where, with protons form water • Occurs in inner membrane of mitochondrial membrane (eukaryote cells) Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Does not involve oxygen • Production of 2 mol ATP • End products: Pyruvate and NADH Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Does not involve oxygen • Production of 2 mol ATP • End products: Pyruvate and NADH Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Aerobic glycolysis • Reoxidizing the NADH via mitochondria • Taking up the pyruvate by mitochondria Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Anaerobic glycolysis • No NAD+ no glycolysis • At high glycolytic rate/or inadequate oxygen glycolysis needed to generate ATP • Emergency system comes to play; reducing the pyruvate to lactate Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Anaerobic glycolysis • There is a lot of lactate dehydrogenase in muscles: • NADH can be rapidly reoxidized (permission of ATP synthesis) • Permits glycolysis to proceed at very fast rate • Vast amount of glucose can be broken down • Produced lactate leaks out; in the liver will be converted into glucose Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Anaerobic glycolysis • Yeast can live entirely on anaerobic glycolysis Lorestan University Biochemistry • Oxidation of glucose: • Glycolysis • Anaerobic glycolysis • Yeast can live entirely on anaerobic glycolysis Does not occur in animals Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle • The main mean energy-generating units of aerobic cells The site of ATP generation Stage 2 of glucose metabolism mainly occurs Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle • Aerobic glycolysis produces: • Pyruvate and NADH in the cytoplasm • To be further oxidized pyruvate must enter the mitochondria • NADH is oxidizes via mitochondria: • Electrons are transported in and oxidized, leaving NAD+ in cytoplasm Note: some cells such as erythrocytes have no mitochondria; ATP must generate by glycolysis; they are glucose dependent Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle • How is pyruvate fed into the TCA • Acetyl-CoA • What is CoA? (CoA-SH) • CoA unlike NAD+ and FAD is not an electron carrier • CoA is an acyl group carrier • Contains pantothenic acid Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle • How is pyruvate fed into the TCA •Contains pantothenic acid Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle •Contains pantothenic acid: • It is just there and apparently quite inert • Provides a recognition group The business end of molecule Lorestan University Biochemistry • Oxidation of glucose: • Citric acid cycle • The CoA molecule carries acyl group as thiol esters; CH3CO—S—CoA -1 • ΔG0 thiol ester is – 31 kJ mol vs. – 20 kJ mol-1 carboxylic ester Lorestan University Biochemistry • Oxidation of glucose: • Oxidation decarboxylation of pyruvate: • CO2 is released (decarboxylation) • A pair of electron is transferred to NAD+ (oxidation) • An acetyl group is transferred to CoA • The reaction is irreversible Pyruvate dehydrogenase Lorestan University Biochemistry • Oxidation of glucose: • Three molecule of CO2 + • Three molecule of NAD are reduced • One molecule of FAD are reduced Lorestan University Biochemistry • Oxidation of glucose • Electron transport to oxygen • Oxidation of NADH and FADH2 take place in inner membrane of mitochondria • The electron transport chain- a hierarchy of electron carriers • Redox potentials: • Problem: transference of electrons from NADH and FADH2 to oxygen Lorestan University Biochemistry • Oxidation of glucose •Redox potentials: • Problem: transference of electrons from NADH and FADH2 to oxygen ΔG0´=-220 kJ mol-1 Lorestan University Biochemistry • Oxidation of glucose •Redox potentials: • Problem: transference of electrons from NADH and FADH2 to oxygen • Redox potential: • Compounds are capable of being oxidised (electron donors) • Oxido-reduction reactions: • Electron donor (reductant); electron acceptor (oxidant) Lorestan University Biochemistry • Oxidation of glucose •Oxido-reduction reactions: • Electron donor (reductant); electron acceptor (oxidant) Redox couple •X and X-; Y and Y- are such couples Lorestan University Biochemistry • Oxidation of glucose •Oxido-reduction reactions: • Different redox couples have different affinities for e- • Lesser affinity means tending to donate electron to another of high affinity ´ • Redox potential (E0 ): • Is a measurement of electron affinity or electron donating of a redox couple Lorestan University Biochemistry • Oxidation of glucose ´ •Redox potential (E0 ) • Importance in biochemical reactions: • Indicator of the direction in which electrons will tend to flow • Important: ´ • Relationship between E0 and free energy changes Lorestan University Biochemistry •Nernest equation • n =number of electrons transferred in the reaction • F= Faraday constant (96.5 kJ V-1 mol-1) Lorestan University Biochemistry • Oxidation of glucose •Electrons are transported in a stepwise fashion • In the cell, transport of electrons to oxygen does not happen in a single step • Chain of electron carriers: Carriers of ever-increasing redox values (decreasing reducing potential) Terminating to the ultimate electron acceptor, oxygen Lorestan University Biochemistry • Oxidation of glucose •Electrons are transported in a stepwise fashion • NADH and FADH2 bump down a staircase Each step being a carrier of the appropriate redox potential and each fall releasing free energy Lorestan University Biochemistry • Oxidation of glucose Harnessing the energy (indirectly results in ATP generation rather than being wasted as heat) Liberation of free energy in manageable parcels Lorestan University Biochemistry • Oxidation of glucose • The oxidation of NADH and FADH2 drives the conversion of ADP and Pi to ATP • The complete process is called oxidative phosphorylation: • 30 mol ATP per mol oxidised ATP Lorestan University Biochemistry Lorestan University Biochemistry • Energy release from oxidation