Digestion And Metabolism Flashcards
(41 cards)
How is ATP changed by oxidative phosphorylation?
- Carbohydrates, fatty acids and amino acids are oxidized to CO2 & H2O
- Intermediates of the reactions donate electrons to form REDUCED energy rich molecules, coenzymes NADH, FADH2
- NADH and FADH2 each donate a pair electrons to electron carriers of the Electron Transport Chain (ETC)
- As electrons are passed down the ETC, they lose free energy
- This energy is used to move protons across the inner mitochondrial membrane and create a H+ gradient
- The H+ gradient drives oxidative phosphorylation: ATP synthesis
- The movement of electrons through the ETC ultimately leads to the phosphorylation of ADP to ATP “Oxidative Phosphorylation”
Explain the structure function off the mitochondria
- Mitochondria – double membrane organelles
- energy powerhouses
- Centre termed the matrix – TCA Cycle enzymes
- Outer membrane is permeable to most molecules
- Inner membrane highly impermeable and highly
- folded into invaginations - cristae
- Enzymes of the ETC and ATP synthase found on the Inner membrane.
- Inner membrane cristae increase membrane surface area and its impermeability allows the establishment of chemical gradients
What is the ETC & OxPhos function?
• Oxidize NADH and FADH2
2
- Generate electrical energy by passing electrons to Oxygen H+
- Create a proton gradient across inner mitochondrial membrane
- Proton gradient drives phosphorylation of ADP to ATP
- 2 stages
- Electron transport then Oxidative phosphorylation
What is the significance of NADH dehydrogenase?
Complex 1
- Will oxidize NADH & reduce Coenzyme Q (CoQ)
- Tightly bound riboflavin-5’-phosphate prosthetic group (FMN) derived from B2 (riboflavin) which reversibly accepts and releases electrons
- Contains iron-sulfur clusters, covalently attached to cysteine residues, which reversibly accepts and releases electrons
- NADH electrons from TCA and PDH, FAO & glycolysis
- Movement of electrons shown in magenta, from NADH to CoQ
- This energy is used to pump 4 protons across the inner-mitochondrial membrane to the intermembrane space
What is the function of complex 2: Succinate-Q-Reductase?
- Succinate dehydrogenase (TCA Cycle)
- Will oxidize succinate and reduce CoQ
- Electrons come from succinate and FAO or glycerol phosphate shuttle (generating FADH2)
- Tightly bound FAD prosthetic group derived from B2 (riboflavin) and adenine
- Contains iron-sulfur clusters
- Contains binding site for succinate and CoQ
- Flow of electrons are shown in magenta
- Does not span the membrane like Complex 1
- No protons are translocate
What is the function of Complex III- Cytochrome b-c1 complex?
- Will oxidize CoQ and reduce Cyt c
- Spans the membrane
- Movement of electrons shown in magenta, from CoQ to Cyt c
- This energy is used to pump 4 protons across the inner-mitochondrial membrane to the intermembrane space
- Flow of electrons shown in green will regenerate CoQ
What is the function of complex IV?g
Complex 4: cytochrome c oxidase
- Oxidized cytochrome c and reduces oxygen to water
- O2 is the final electron acceptor
- Spans the membrane
- Contains two heme groups which are each positioned close to a bound copper atom (binuclear centers)
- Movement of electrons shown in magenta, from Cyt c to oxygen
- This energy is used to pump 2 protons across the inner-mitochondrial membrane to the intermembrane space
What are the mobile electron carriers?
• Coenzyme Q or Ubiquinone or Q10 so called because of
ubiquitous “expression” and the presence of its
10-isoprenoid residue hydrophobic tail
• Non-protein lipid soluble molecule
• Can accept 2 electrons from donors and release a single electron to
acceptors
• Cytochrome c: small heme protein bound to the
intermembrane space side of the inner membrane
• Heme group is Heme c which is covalently linked to the protein
• Acts as an electron shuttle between Complex III & IV
What is the structure function of ATP synthase?
• Multi-subunit enzyme: F0 and F1 portions
• F0 in the inner mitochondrial matrix contains the
proton pore
- F1 in the mitochondrial matrix contains the catalytic activity (ATP synthesis)
- Protons that have been pumped to the cytoplasmic side of the IMM re-enter the matrix through an H+ channel in the F0 domain of ATP Synthase
- This drives rotation of the C ring which then drives ATP synthesis
- One complete rotation of C ring uses 8 protons and produces 3 ATP
What is the P/O ratio?
- Complex I and III pump 4 H+ & Complex IV pumps 2 H+ into intermembrane space
- ~3-4 H+ required to synthesize 1 ATP
- NADH entering at Complex I pumps 10 H+ = 2.5 - 3 ATP
- FADH2 entering at Complex II pumps 6 H+ = 1.5 - 2 ATP
- P/O ratio is a measure of the number of high-energy phosphate bonds synthesized per atom of oxygen consumed i.e. The number of ATP per 1⁄2 O2
- P/O ratio for NADH = ~3
- P/O ratio for FADH2 = ~2
How much ATP is generated per molecule of glucose?
Glycolysus- substrate Level phosphorylation - 2 ATP
2 NADH generation- 4 or 6 ATP
Puruvate dehydrogenase- 2 NADH- 6 ATP
Citric acid-
Substrate level phosphorylation- 2 ATP
6 NADH- 18 ATP
2 FADH2- 4 ATP
TOTAL= 36 or 38 ATP
What is the purpose of NADH?
- NADH cannot cross the Inner mitochondrial membrane
- Shuttle is required to deliver NADH electrons from cytosol (glycolysis) to the mitochondrial matrix
- FADH2 will donate electrons to CoQ
- NADH will donate electrons to Complex I, regenerating NAD+
Explain oxidative phosphorylation & the Chemiosmotic theory
Proton motive force
Mitchell’s Chemiosmotic Theory: 2 steps
Step 1
• As electrons flow down electrochemical potential, protons are pumped into the intramembrane space
• Protons are pumped into intramembrane space at complexes I, III & IV
• Protons cannot re-enter the matrix alone
Step 2
• This creates a pH gradient that is relieved by pumping protons back thru F0F1-ATP synthase (Complex V). The energy released in this process is coupled to ATP synthesis from ADP and Pi.
• pH different across the inner membrane ~0.75 pH units
What are the inhibitors ofETC ?
Decrease in ATP synthesis, ETC activity & oxygen consumption
Inhibitirs of complex I Amytal: barbiturate Rotenone: insecticide Piericidin A: bacterial antibiotic Does not affect flow from complex II-
Complex III-cytochrome reductase inhibiitirs
Antimycin A: antibiotic Inhibits cyt b
Conplex IV inhibitors
Cyanide: CN- Azide: NaN3 Hydrogen sulfide: H2S Carbon monoxide: CO All inhibit heme a3-Cu
Complex V ATP synthase
Oligomycin: antibiotic
What are the inhibitors of ETC complexes I, III & IV?
• Will reduce electron transport and establishment of a proton gradient
• ATP synthesis depends on the proton gradient, thus a reduction in electron
transport results in a reduction of ATP synthesis
What are the inhibitirs of ATP synthase?
- Electron transport is initially unaffected, and establishment of a proton gradient will occur
- Once a maximum gradient has been established, the electron flow will be inhibited
- Protons can leak back into the matrix by facilitated diffusion of the protons with “uncoupling proteins” like thermogenin
- This “uncouples” the activity ETC from ATP synthase
- How does the ATP move from the mitochondrial matrix into the cytosol?
- How does the ADP and move from the cytosol to the mitochondrial matrix to be used as substrate for
ATP Synthase?
- ATP and ADP transported via an Antiport – 1:1 exchange, ATP out, ADP in
- Driven by the electrochemical gradient and membrane potential
- Pi is transported together with a H+ symport not shown
What is the function of Adenine nucleotide translocase?
• Adenine nucleotide translocase (ANT): unidirectional exchange of ATP for ADP (antiport)
• Symport of Pi and H+ is electroneutral
What is atractyloside?
Atractyloside; toxic glycoside (molecule with a sugar and a noncarbohydrate element) from thistle plant Atractylis gummifera
• Binds the outward facing (inter-membrane space) portion of the adenine nucleotide transporter
What is Bongkrekic acid?
respiratory toxin produced in coconuts contaminated with Burkholderia gladioli
• Binds the inward facing (matrix) portion of the adenine nucleotide transporter
What are the effects of Atractyloside and Bongkrekic acid?
Effect of both are similar to oligomycin
Complex V can’t dissipate proton gradient if inhibited or has no substrate
ETC will shut down as well, failure to dissipate proton gradient
What is the final aacceptor of electrons?
Oxygen
What happens in ETC in hypoxia?
- Hypoxia decreases the rate of ETC and ATP production.
- A drop in cellular ATP increases anaerobic glycolysis and lactic acid production, anaerobic glycolysis cannot meet most tissue demands (neural tissue, cardiac muscle).
- Myocardial infarction can result from hypoxia, leading to tissue damage, leakage of intracellular enzymes (CK1, CK2, LDH) and troponin I and T.
Explain uncoupling of oxidative phosphorylation
• Uncoupling occurs when H+ re-enter the mitochondrial matrix without going through ATP synthase
- “Dissipation” of the proton gradient results in:
- Reduction in ATP synthesis
- Increase activity in all complexes of ETC activity (not slowed down by proton gradient)
- Increase in Oxygen consumption (Complex IV activity is increased)
- Release of energy as heat
- Proteins and synthetic uncouplers
