ETC and oxidative phosphorylation and ox stress-Mitsouras Flashcards
Coupling of metabolic reactions
energetically linking reactions.
a spontaneous, energy-yielding reaction drives an energy-requiring, non-spontaneous reaction==> the Gs are additive
reactions share intermediates
ATP hydrolysis drives other energy-requiring reactions
How is ATP produced through oxidative phosphorylation?
Electrons are donated from NADH and FADH2 and enter the ETC–> lose Gibbs free energy as travel along the ETC==> free energy drives ATP synthesis
What are the components of the ETC?
Complexes I-IV with e- carrying groups–> integral multi-protein complexes
Accept NADH & donate e-. arranged in specific order in inner mitochondrial membrane
Ubiquinone (Coenzyme Q) & cytochrome C –>soluble & shuttle e- from/to complexes (mobile)
e- follow specific path dictated by standard reduction potentials
complex IV catalyzes the creation of H2O
Complexes 1, 3, and 4 pump H+ out of the matrix, into the inter membrane space
NADH enters complex 1
FADH2 enters complex 2
Co Q carries e-s from complex 1 and 2 to cyt c
Cyt c carries e-s from Co Q to complex 4 to donate e-s to O2
what is the chemiosmotic hypothesis?
how the proton gradient is coupled to ATP synthesis
- e-flow through ETC==> H+ from matrix–> intermmbrane space
- H+ gradient==> proton-motive force
- H+ back into the matrix (down [gradient])–> ATP synthesis by ATP synthase
structure of ATP synthase and how many ATP are produced for NADH and FADH2
2 catalytic parts: F0–> rotation of c-ring when H+ present and F1–> synthesize ATP
and a proton channel
3ATP/NADH
2ATP/FADH2 (bypasses complex 1)
total energy yield from glucose oxidation
38 ATP if the malate shuttle was used
36 ATP if the G3P shuttle was used
What are the inhibitors of ETC and what are their sites of inhibition?
all block electron transport –> no ATP produced
Complex 1: amytal, rotenone, and piercidin A
Complex 3: Antimycin A
Complex 4: CO, CN-, sodium azide, hydrogen sulfide
What are the uncouplers of oxidative phosphorylation and where are there sites of action?
H+ leaks across membrane–> disrupt gradient–> uncouple e- flow and ATP synthesis
energy is dissipated as heat (fever, hyperthermia
salicylate (aspirin) is a partial uncoupler
Thermogenin (UCP1), DNP: increase permeability to H+ on the inner mitochondrial membrane
oligomycin: inhibits ATO synthesis directly through interacting with complex 5.
Leber’s Hereditary Optic Neuropathy (LHON):
caused by mutations in any of several mt genes encoding Complex I subunits
- progressive loss of central vision & blindness (degeneration of optic nerve)
Mitochondrial encephalopathy, lactic acidosis & stroke-like episodes (MELAS):
caused by mutations in any of several mt genes (genes encoding mt tRNAs ex. leucine, glutamine or genes encoding Complex I subunits)
- progressive neurodegenerative disease & stroke like episodes
Myoclonus, Epilepsy and Ragged-Red Fiber disease (MERRF):
- caused by mutations in any of several mt genes encoding mt tRNAs ex. phenylalanine, serine
- progressive myoclonic epilepsy, slow progressive dementia
Leigh syndrome (subacute necrotizing encephalopathy):
- caused by mutations in mt genes encoding Complex IV subunits
- atrophy of optic nerve
- respiratory abnormalities
- hypotonia & spasticity
Note: Leigh syndrome also caused by PDH mutations (X-linked)
What are the different types of ROS?
Free radicals are molecules with highly reactive unpaired e- that can exist independently (i.e. not as part of an enzyme)
Very detrimental/toxic to cells because they are unstable and look to donate/accept their unpaired e-==> leads to chain reactions and converts other molecules to free radicals
Involved in a number of diseases (ex. cancer, Parkinson’s disease, diabetes, aging)
ROS=reactive oxygen species arise from O2. 1. O2- superoxide anion 2. H2O2 Hydrogen peroxide (not a free radical but can create free radicals when reacts with transition metals 3. OH* Hydroxyl radical
Formation of ROS
During aerobic respiration by Coenzyme Q on ETC --> e- can pass from Co Q to O2 in the passage of complex 1-->3 ==> forming O2- *major source of O2- in cell antimycin A (complex 3 inhibitor can increase likelihood of O2- formation)
During drug/xenobiotic detoxification by cytochrome P450 mono-oxygenases
-P450s catalyze transfer of e-from NADPH (through transition metal) to O2 and to target molecule–> leakage of e- can form O2-
By oxidase enzymes (mitochondrial, cytoplasmic & peroxisomal)
-can form H2O2 or O2-
By reacting with free metal ions–> Haber-Weiss & Fenton reactions (require free metal ions such as Fe2+)
- create OH*=the most damaging free radical
- major sources of OH in the cell–> ionizing radiation is secondary source
By ionizing radiation (cosmic rays, X rays, radioactivity etc) & toxic chemicals
-forms OH* (secondary to free metal reactions)
How do ROS cause damage to the cell?
OH· and O2- are free radicals–>unstable & seek stability by donating or accepting e- (from other molecules)
H2O2 doesn’t cause damage directly (non-radical) but can diffuse into & through membranes & generates OH· (Haber-Weiss & Fenton reactions)
O2- cannot diffuse far from site of origin but can react with H2O2 and generate OH· (Haber-Weiss reaction)
OH· is most damaging of ROS species because it is most reactive
ROS cause cellular damage via 3 major effects –>injury to lipids, carbohydrates, proteins & DNA
-damage to lipids: lipid peroxidation–> lipid degradation–> membrane damage
- damage to proteins: pro, his, arg, met vulnerable to OH* attack–> protein cross linking, fragmentation
- damage to carbs: advanced glycation end products (AGEs) occur as a result of hyperglycemia in DM
- damage to DNA: backbone cleavage, strand breaks, base alterations by OH* attach–> mutations and apoptosis
