Lecture 26- ATP production & oxidative phosphorylation Flashcards
What is metabolism?
Living systems acquire & use free energy in order to carry out their functions
2 divides of metabolism
Catabolic
Anabolic
Catabolic metabolism
The degradation of nutrients to salvage components & gain energy
Anabolic metabolism
The synthesis of biomolecules for simpler components
Autotrophs
Synthesis all cellular components from simple molecules
Photoautotrophs
Use light to produce carbohydrates which are oxidised giving free energy
Chemolithotrophs
Obtain free energy from compound oxidation
Heterotrophs
Oxidise carbohydrates, lipids and proteins
Classification of oxidising agents
Obligate aerobes- require O₂
Anaerobes- use sulphate or nitrate
Vitamins
Organic molecules obtained from diet
Water soluble (coenzyme precursors)
Fat soluble (required in diet eg. vitamin C)
Degradative pathways
Often converge on common intermediates
Further metabolised in central oxidadative pathway
Biosynthetic pathways
Carry out the opposite
Few metabolites are the starting points
Metabolic roles of liver (learn overview)
Metabolism of carbohydrate, lipid, amino acids
Metabolic roles of muscle (learn overview)
ATP production for muscle contraction
use glycogen, glucose, fatty acids an ketone bodies as fuel
Metabolic roles of brain (learn overview)
Nerve transmission (high ATP requirement)
Use glucose and ketone bodies as fuels not fatty acids
Metabolic roles of adipose (learn overview)
Fat synthesis & storage
-ve ΔG= ….
ΔG=0 = ….
+ve ΔG= …
-ve ΔG= favourable
ΔG=0 = equilibrium
+ve ΔG= unfavourable- usually require input of ATP
Forms of cellular energy curency
Thioester bond-containing compounds
Reduced coenzymes
ATP
NAD+ accepts … electron(s) and … proton(s)
2 (donated to ETC)
1
FAD+ accepts … electron(s) and … proton(s)
2 (donated to ETC)
2
ATP as an energy carrier
Biological importance depends on the free energy change that accompanies cleavage of phosphoanhydride bonds
Standard free energy of hydrolysis is -7.3 kcal/mol
Reactions with large +ve ΔG are possible by coupling with 2nd process with large -ve ΔG
Substrate level phosphorylation
Direct addition of phosphate group to ADP to form ATP
Oxidative phosphorylation
Energy-rich molecules are metabolised by oxidative reactions
Metabolic intermediates donate electrons to NAD+ & FAD to form NADH + H+ and FADH₂
As e- passes down ETC, they lose free energy- used to pump H+ across inner mitochondrial membrane -> H+ gradient which drives ATP synthesis from ADP + Pi
ETC loaction
Inner mitochondrial membrane
impermeable so requires specialised transport systems
Highly convoluted crisae increase surface area
Mitochondrial matrix contains enzymes responsible for oxidation
Organisation of ETC
IMM contains 5 separate protein complexes and 2 mobile electron carriers
Ultimately electrons combine with O₂ to form H₂O
Complex I
At least 34 polypeptides
NADH binds to Complex I and electrons transferred to CoQ
Electron’s energy loss is used to pump 4H+ across the membrane
Complex II
Enzyme of TCA cycle-succinate dehydrogenase
Accept electrons from FADH₂
Transfers electrons to CoQ vis Fe-S proteins
No energy is lost so no protons are pumped at Complex II
Coenzyme Q
Small lipid molecule- hydrophobic quinone
Diffuses rapidly with IMM
Accept electrons from FE-S proteins from Complex I and Complex II
Complex III & Cyt c
Both cytochrome proteins
Cut C is peripheral protein
Electrons transferred from Complex III to Cut C to Complex IV
At Complex III energy loss is used to pump 4 H+ across inner membrane
Complex IV
The only electron carrier in which the heme iron has co-ordination site for O₂
Transfers pair of electrons to 1/2 O₂ which is reduce to form H₂O
2 protons pumped across IMM
Why are electrons transferred?
The transfer of electrons does the ETC is energetically favourable
NADH is a strong electron donor
O₂ is a strong electron acceptor
Chemiosmotic hypothesis
Proton pumping across the IMM creates a H+ gradient
Drives ATP synthesis via ATP synthase
ATP synthase
Protons pumped to the cytosolic side of mitochondrial membrane re-enter the matrix by passing through F₀ proton channel
As protons pass down channel they drive the rotation of the C ring of F₀ which causes conformational change in beta subunit of F₁ domain
ATP yield of oxidative phosphorylation
Every pair of electrons from NADH- 2.5 ATP generated
Every pair of electrons from FADH₂- 1.5 ATP generated
So, from one glucose molecule 30 ATP generated by oxidative phosphorylation
P/O ratio
Number of ATP molecules formed per oxygen atom
Inhibitors of electron transport chain
Prevent the passage of electrons down ETC and so prevent H+ being pumped across IMM
Inhibit ATP synthesis
Uncouplers of ETC & ATP synthesis
Chemicals- dinitrophenol
Natural proteins- uncoupling protein (UCPs)
Other final electron acceptors
Allow organisms to live in anaerobic conditions
eg. NO₃ which forms NO₂, N₂O or N₂
SO₄ which forms S or H₂S
CO₂ which forms CH₄ (methanogenesis)
