number Done by Corrected by Doctor Nafeth Abu Tarboush

Transcription

1 number 8 Done by Ali Yaghi Corrected by Mamoon Mohamad Alqtamin Doctor Nafeth Abu Tarboush 0 P a g e

2 Oxidative phosphorylation Oxidative phosphorylation has 3 major aspects: 1. It involves flow of electrons from NADH and FADH2 in TCA cycle through a chain of membrane bound carriers (prosthetic groups), and keep transporting them from one complex to another until they reach oxygen; the final electron acceptor. Note: the force that makes the electrons move through complexes of ETC is the potential difference. Note: Because there is a difference in potential, there must be a difference in energy (ΔG= -nfδe). 2. The energy produced from the movement of electrons in the electron transport chain is used to pump protons from the matrix of the mitochondria to the intermembraneous space through pumps in the inner mitochondrial membrane. Note: The free energy available is exergonic Note: The inner mitochondrial membrane is impermeable to anything even to H+. 3. The transmembrane flow of protons down their electrochemical gradient provides the free energy for synthesis of ATP (energy is used to 1 P a g e couple inorganic phosphate with ADP to produce ATP). Note: Oxophos was discovered by Peter mitchel in 1961(chemiosmotic theory). How does the electron transport chain generate ATP from NADH?

3 NADH can move freely through the solution (martix). Enzymes that are used to produce NADH are: a. Isocitrate dehydrogenase b. Alfa-ketoglutarate dehydrogenase complex c. Malate dehydrogenase. NADH moves to its electron acceptor in ETC which is called complex 1. It is the point of transmitting electrons from NADH. Complex 1 takes electrons from NADH as H- (hydride ion). Notice that Complex 1 (NADH dehydrogenase) is an oxidoreductase; because it contains FMN which acts as an acceptor for electrons from NADH and transfer them to the iron-sulphur clusters. The first thing that takes electrons from NADH is FMN and it turns into FMNH2. Now complex 1 is reduced. Note: Iron-sulfur clusters are present in complex 1. Note: Fe can transport 1 electron at a time, so it transports 2 electrons in two stages. How does the electron transport chain generate ATP from FADH2? FADH2 can't move freely in the matrix because it is always bound to a protein.in this case it is succinate dehydrogenase in ETC. Succinate dehydrogenase is the only direct connection between citric acid cycle and electron transport chain, and it is suspended in the matrix surface of the inner membrane. So, Succinate dehydrogenaseis complex 2. It has FAD and iron-sulfer clusters so it works as oxidoreductase. Complex 1 gives its electrons to complex 3, so does complex2 through the Co-Q (ubiquinone). (Complex 1 and 2 do not have any connection). How do electrons move from complex 1 and 2 to complex 3? 2 P a g e

4 Electrons move through a lipid soluble electron carrier that has a hydrophilic part that attaches to electrons. This material is called coenzyme q or ubiquinone. The carrier must be lipid soluble; because if a hydrophilic carrier is used (its place would be on the surface of membrane), it can't transport complex 2 electrons to complex 3, because complex 2 isn't spanning the membrane. Ubiquinone Ubiquinone is a cyclic di-ene structure + long hydrocarbon chain. Carries electrons through the IMM(inner mitochondrial membrane). Can accept either 1 electron (semiquinone) or 2 electrons (ubiquinol), because it has 2 carbonyl groups. Note: Co-Q is prescribed to patients who suffer from myocardial infarction (dead heart tissue), because it increases the amount of ATP produced per time; compensating dead tissue. Note: Toxic materials that attack complex 3 cause death. The damage from toxins that attack complex 1 or 2 aren't as bad as complex 3. Complex 3 Complex 3 is called cytochrome bc1. Cytochrome means that the protein works as an electron transporter and has a heme group (six coordinate heme). This complex has different types of heme (heme b and c), and has iron sulphur clusters. These features make it work as an oxidoreductase; reduction by getting electrons from Co-Q and oxidation by giving electrons to cytochrome C. How do electrons move from complex 3 to complex 4? Since these complexes are spanning the membrane, the carrier is outside the membrane. The carrier is a protein called cytochrome c, which has the capacity of transporting 1 electron per time. Complex 4 is called Cytochrome C oxidase because it oxidizes Cytochrome C; by taking the transported electron. وال ( hemoglobin. Complex 4 has higher affinity toward O2 than myoglobin and (كيف بدو يدخل الخلية Complex 4 3 P a g e

5 It is an oxidoreductase since it turns O2 into water, and it works as an oxidoreductase because it has 2 copper atoms (copper a + b) and 2 heme (a+a3) groups. Copper has 2 oxidation states, and O2 binds to heme when it is reduced. The movement of electrons: As electron as is, like in the heme. Hydrogen atoms: FADH2. Hydride ions: NAD to NADH. ATP generation from NADH (per 2 electrons moving) 1- When complex 1 gives 2 electrons from NADH to ubiquinone, the difference in energy is used to pump 4 H+ ions to inter membranous space. That's why complex 1 is spanning the membrane. 2- When electrons move from Complex 3 to cytochrome c, the energy produced is used to pump 4H+ ions. 3- When electrons move from complex 4 to O2, the energy produced is used to pump 2 H+ ions. Net H+ ions pumped:10 ions. Since 4H+ ions produce 1 ATP, NADH produces 2.5 ATP. ATP generation from FADH2 (per 2 electrons moving) 1- When Complex 2 gives 2 electrons to ubiquinone, the difference in energy is almost zero, so no H+ Ions will be pumped. Complex 2 doesn't span the membrane. 2- Same as NADH 3- Same as NADH Net H+ ions pumped:6 ions FADH2 produces 1.5 ATP Requirements of OxPhos: 4 P a g e

6 1. Redox reaction: electron donor (NADH or FADH2) & electron acceptor (O2) 2. Impermeable inner mitochondrial membrane 3. Proteins of the electron transport chain and electron transporters 4. ATP synthase 5. Potential difference between donor and acceptor ATP synthase: complex 5 It has 2 parts: F0 in the membrane, and F1 in the matrix (where ATP is synthesized) F0 portion: It is cylindrical in shape It can rotate within the membrane It is connected to (a) subunit It is composed from 12 C subunits and an alpha subunit. (a) subunit is where the H+ ions pass through. It isn't a continuous channel, it is separated. F1 portion: 3 alpha subunits and 3 beta subunits arranged alternatively. Alfa subunits are structural. Beta are catalytic subunits. Angled Gama subunits are produced from C subunits. Mechanism of working: The proton passes in the channel, faces a C subunit (which has deprotonated glutamic acid), then H+ attaches to this subunit and glutamic acid becomes protonated (neutralize), then it rotates exposing another c subunit, and so on. This process continues until protonated glutamic acid reaches the other opening of the channel (a subunit), and shuts the H+ ion toward the matrix. The reason for doing this is to make rotation in C subunits. 5 P a g e

7 Note: pka determines the attachment and detachment of H+ ions to c subunit. While the C subunits are rotating in the membrane, the angled gama subunit hits different beta subunits with each rotation. When a subunit hits another subunit, a conformational change happens. And there are 3 conformational changes: open, loose and tight. At first it is open. Open has high affinity for ADP with in-organic phosphate, when a conformational change is happening, it is turned into loose, which makes ADP and Pi close together, Then another change takes place that makes the subunit tight and generate ATP. And it comes back to open conformation, which has low affinity for ATP, so ATP is released. Note: ATP synthase can move in reverse, also (make ADP +Pi from ATP). General notes: Oxidative part is the redox reactions in the electron transport chain. Phosphorylation part is the part that produces ATP. Electrons will keep moving through different complex until it reach O2, but no ATP is produced. ETC does not produce ATP. These processes are always coupled to each other. 6 P a g e

8 The inner membrane is impermeable to anything even to H+ Pumping means active transport(against the electrochemical gradient) If the H+ will keep pumping, the H+ will stop being pumped through the IMM, so the electrons will stop moving through the ETC. H+ aren't able to come back unless through complex 5. 7 P a g e