T2 L3 Mitochondrial respiratory chain Flashcards
Describe the mitochondrial membrane structure
Outer membrane - freely permeable to small molecules & ions
Inner membrane - impermeable to small molecules & ions, including H+. ETC is located here
Describe complex I
NADH dehydrogenase
Catalyses 2 simultaneous & coupled processes
1) Electrons are passed to FMN to produce FMNH2
2) Electrons then transferred to a series of iron-sulphur clusters
3) Electrons then transferred to coenzyme Q or ubiquinone
Pumps 4 protons from the matrix into the intramitochondrial membrane (endergonic transfer)
NAD+ goes back to the citric acid cycle to pick up electrons & be reduced
What is the reaction at complex I?
NADH + H+ + Q = NAD+ + QH2
Describe complex II
Succinate dehydrogenase
Only complex which doesn’t pump protons
1) Electrons of FADH2 pass to complex II
2) Electrons pass from complex II to ubiquinone
Describe complex III
Ubiquinone cytochrome C oxidoreductase
Describe complex IV
Cytochrome oxidase
Proton pump
Carries electrons from cytochrome C to molecular oxygen
Produces water
What do the 3 specific systems in the mitochondrial membrane do?
Transport ADP & Pi into the matrix
Synthesis ATP
Transport ATP into the cytosol
What are the 3 systems in the inner mitochondrial membrane?
Adenine nucleotide translocase
Phosphate translocase
ATP synthase
Describe adenine nucleotide translocase
Integral protein of inner mitochondrial membrane
Transports ADP3- from intramitochondrial membrane space into the matrix
ADP3- is exchanged for an ATP4- molecule
What is an anti porter?
Brings one thing in and one thing out
What is atractyloside
Glycoside isolated from a thistle
Specific inhibitor of adenine nucleotide translocase
Describe phosphate translocase
Essential for oxidative phosphorylation & synthesis of ATP
Transports phosphate & hydrogen ions into the matrix
Favoured by transmembrane proton gradient
What is a symporter?
Brings two things in or two things out
Describe ATP synthase
F-type ATPase
2 functional domains
Beta subunits are arranged alternately with alpha subunits. Form a knob-like structure that is held by a stalk of the gamma & E (symbol). Delta subunits interacts with 2 b subunits of F0.
What are the 2 functional domains of ATP synthase?
F0 - oligomycin sensitive proton channel. Comprised of 3 different subunits: a,b&c. Forms a complex of 13-15 subunits. Subunits c1-10 are arranged in a circle.
F1 - ATP synthase. Comprised of 5 different subunits: alpha 3, beta 3, gamma, delta & E (symbol)
Describe the theory of rotational catalysis
3 beta subunits take it in turns to catalyse synthesis of ATP
Any given beta subunit starts in a conformation for binding ADP & Pi
Then changes conformation so the active site now binds the ATP product tightly
Then changes conformation to give the active site a very low affinity for ATP so ATP is released
How much ATP is yielded from 1 molecule of glucose
30 or 32
How do uncouplers dissipate the pH gradient?
They transport H+ back into the matrix of the mitochondria & bypass ATP synthase. This severs the link between electron flow & ATP synthesis with the energy being released as heat.
Describe uncoupling reagents
It can occur naturally
UCP1 is found in brown adipose tissue & has a specific H+ channel through which the H+ concentration can be dissipated & energy is released as heat
Usually weak acids or bases & are hydrophobic
Why are uncoupling reagents hydrophobic?
Allows them to freely diffuse through the inner mitochondrial membrane
How is brown adipose tissue adapted for thermogenesis
Specialised for heat generation
High numbers of mitochondria
Mitochondria contain thermogenic (UCP-1)
Important in newborns & may have a role in obesity/diabetes
What is DNP?
Exogenous uncoupler
Weak acid
Crosses the membrane by ferrying H+ across
Each DNP molecule collects a proton from inter membrane space & moves through the membrane with it then deposits proton in the matrix.
Can return through the membrane to collect another proton
Toxicity arises from liver damage, respiratory acidosis & hyperthermia
