Lecture 4 Flashcards
(18 cards)
Uncoupling
Protons would no longer need to pass through the core of ATP synthase as they would be able to diffuse back into the inner mitochondrial matrix. Hence, no ATP is produced and the gradients dissipates.
Consequences of uncoupling
- No driving force for ATP synthesis as there’s no back pressure to stop H+ pumping and no restriction on H/e- movement down the transport chain to O2.
-Instant regeneration of NAD from NADH causing massive fuel O2 and O2 consumption rate.
-No ATP synthesis = low ATP levels = death
Dinitrophenol
Hydrophobic when protonated (can move freely across membrane), weak acid. It picks up protons from the inter mitochondrial matrix, diffuses through the membrane and delivers it into the innermitochondrial matrix
DNP mechanisms
Hijacks ATP synthase’s ability to allow protons to diffuse through the membrane. It dissipates the proton gradient, causing massive weight loss and heat production. DNP used in explosives.
Natural uncoupler
Uncoupling protein-1 (UCP-1) only found in brown adipose tissue. It can dissipate the proton gradient by opening UCP-1 pore. AKA thermogenin.
thermogenin
Function is to generate generate especially in small mammals and hibernating animals. Under hormonal control (noradrenaline) control that stimulates fatty acid use.
ETC
Inter membrane space has a higher proton concentration than matrix. ATP Synthase sits in the membrane which uses the protein gradient to drive ATP synthesis where proteins flow from the inter membranous space to the matrix, causing it to rotate and phosphorylate ADP to ATP. ETC establish and maintain proton gradient. Complex 1,3 and 4 directly pump protons from matrix to the inter membrane space. Complex 2 doesn’t directly pump protons but it promotes proton pumping in C3 and 4. Energy for proton pumping is provided by transferring electrons through REDOX reactions. NADH delivers 2 electrons to C1 where they undergo REDOX reactions. Energy produced in REDOX allows 4 protons to be pumped. Electrons are donated to coenzyme Q which takes them to complex 3. FADH2 donates electrons to C2 where they also undergo redox before donating to coenzyme Q. Coenzyme Q donates electrons to C3 where it undergoes more redox reactions (2 protons pumped) before being carried to C4 by cytochrome C. At C4, 4 electrons converts oxygen to 2 water molecules. Proton gradient is strengthened a 4 protons from matrix is used for this and another 4 are pumped into the inter-membrane space. Lack of O2 = ETC halting. NADH allows 10 protons to be pumped, FADH2 allows 6 protons to be pumped.
NADH pathway through ETC
NADH -> C1 -> Q -> C3 -> C4
FADH2 pathway through ETC
FADH2 -> C2 -> Q -> C3 -> C4
Ubiquinone
UQ is very hydrophobic and lives in the inner mitochondrial membrane. UQ picks up Hs from C1 and C2 where is is reduced to UQH2. UQH2 transfers Hs to C3.
Cytochrome C and Fe
Cyt C picks up from C3 and gives the e- to C4. Cyt C has prosthetic group which contains an Fe atom. Changes from ferrous to ferric as it loses electrons and vice versa it accepts the electrons. Fe does NOT carry H+.
Electrochemical gradient characteristics
The energy in the gradient is based on both charge and concentration.
chemical gradient
The presence of more H+ on the p side than on the n-side.
Free radicles
Electrons in the UQ pool can react with molecular O2 which produces free radicles. They may alter DNA or damage proteins. The formation of free radicles is more likely to happen if there is a back-up in the ETC.
F0F1 ATPase structure
The F₀ channel is made of around 12 cylindrical proteins.
As H⁺ enters, it causes rotation of the gamma subunit.
This rotation changes the shape of the β subunits of F₁ in three ways:
Accepting ADP and Pi
Reacting them together to form ATP
Releasing ATP
The γ subunit spins, pressing on the α and β subunits, causing conformational changes.
The sigma subunit holds the whole structure in place.
Think of it like mixing a cake:
γ = spoon
α/β = the mixture
σ = your hand holding the bowl
ATP ‘wastage’
The H⁺ gradient is not only used for making ATP — it’s also used for transport. When ATP is made in the mitochondrial matrix, it needs to be exported to the cytoplasm.
To do this, a proton is used (indirectly) through exchange mechanisms. At the same time, ADP and Pi (the substrates for making ATP) need to be brought into the matrix — which also costs a proton.So, some of the H⁺ gradient is “wasted” on transport instead of ATP synthesis.
Glycerol 3-Phosphate Shuttle
cytoplasmic NADH transfers H⁺/e⁻ to dihydroxyacetone phosphate (DHAP), converting it to glycerol 3-phosphate. Glycerol 3-phosphate moves to the inner mitochondrial membrane and passes H⁺/e⁻ to FAD. Electrons from FADH₂ enter the ETC, bypassing Complex I. 6 H⁺ pumped.
Malate Shuttle
cytoplasmic NADH transfers H⁺/e⁻ to oxaloacetate, forming malate. Malate enters the mitochondrial matrix, where the reverse reaction occurs — malate is converted back to oxaloacetate, passing H⁺/e⁻ to NAD⁺.
NADH is regenerated in the matrix and donates electrons to Complex I.This allows for 10 H⁺ to be pumped. However, there is a risk of running out of oxaloacetate, so the glycerol 3-phosphate pathway may be used instead.
