Lecture 12: Oxidative Phosphorylation - Electron Transport Chain

Is the citric acid cycle catabolic of anabolic?

both - when pyruvate is broken down into CO2 (Catabolism), when intermediates carbon skeleton is used to make amino acids (anabolism)

What is amphibolic?

can be used in the context of both catabolism and anabolism

What type of regulation exists in the citric acid cycle?

things made by the citric acid cycle can also inhibit it: ex. products through catabolism: ATP, NADH and succinyl-CoA - (a place where things come of to do other things - can be used in other processes)

What is an example of a 5-C compound?

a-ketoglutarate

After the citric acid cycle why have we made all this NADH and FADH2?

because they carry energy - which can be used/removed in oxidative phosphorylation

How can the reduced electron carriers NADH and FADH2 help in the production of ATP?

need to make oxidized electron carrier because glycolysis needs them

What is oxidative phosphorylation?

high energy electrons in reduced electron carriers are passed along the mitochondrial electron transport chain in a process that makes ATP and the final electron acceptor is O2

How does oxidative phosphorylation happen (as a concept)?

as the electrons are passed down the chain - they lose energy, which is captured, each carrier has more affinity for electrons than the last (always in the direction of increased reduction potential)

Why is oxidative phosphorylation done in steps?

because if it was done in one step it would only accomplish one task, and waste a lot of energy - overall -220 kj is made overall - a lot of energy

Which formula is used to calculate the energetics of reduction reactions?

ΔG = -nFΔE

ΔE acceptor - E donor

Where does NADH enter ETC?

at complex 1

Where does FADH2 enter ETC?

at complex 2

What happens to NADH in complex 1?

it loses an e- (oxidation) - using FMN (flavin mononucleotide) and Q is protonated to QH2

What happens to FADH2 in complex 2?

comes in directly from the succinate to fumarate reaction, e- comes off, make QH2

How is the proton pump created in complex 1?

as e- are put on Q, H+ are pumped out

What route do protons take when going through the proton pump?

the matrix side to the intermembrane space side - creates a voltage gradient

How do the e- go to coenzyme Q in complex 1?

FMN passes electrons through to iron sulphur cluster containing protein, then onto Q

How many protons are pumped out in complex 1?

per NADH 4 protons are pumped out

What is the structure of iron-sulphur clusters?

in complex 1 - made of iron and sulphur, S comes from cysteine

What is ubiquinone?

coenzyme Q - when fully oxidized - has ketone group

What is ubiquinol?

conenzyme QH2 - when fully reduced

What is semiquinone radical?

QH - has only 1 proton

How to e- go to coenzyme Q in complex 2? (rxn)

Succinate + Q ←→ Fumarate + QH2 - no protons moved

What occurs in complex 3 of ETC?

Q cycle

What are cytochromes?

part of an iron sulphur cluster - can only receive 1 e-/H+

What is the main questions of the Q cycle?

how to move 2 e- on QH2 with cyctochrome that only takes 1

What is the Q cycle?

QH2 comes through iron sulphur cluster to cytochrome C - 1 e- comes off other is put on another Q (becoming QH), another QH2 comes, cytochrome again takes 1 e-, other e- is put on QH to make QH2 - overall done twice - 2 e-/H+ per QH2 put in - getting 1 QH2 back

What do cytochromes resemble?

heme group

What occurs in complex 4?

transfers electrons from cytochrome C to O2

• takes 4 e- from 4 cytochromes and 8 H+ to make H2O - 1 O2

Which inhibitor inhibits are complex 1?

rotenone

Which inhibitor inhibits are complex 2?

antimycin A

Which inhibitor inhibits are complex 4?

CN- or CO

How is the reduction of these compunds resulting in ATP synthesis?

through chemiosmotic coupling

Per NADH how many protons are pumped?

10 protons

How many protons are pumped at complex 1?

4

How many protons are pumped at complex 3?

2 per QH2

How many protons are pumped at complex 4?

2 protons per ½ O2; 4 protons per O2

What is chemiosmotic coupling?

allows osmosis of protons across a membrane - but we are going to couple that to a chemical rxn to make ATP

What charge does the intermembrane space have?

positive

What charge does the matrix have?

negative

What happens to ATP synthase?

turning of gamma subunits caused by proton movement, causes strain - causing conformational change in the beta subunits - driving ATP synthesis

At all times beta subunits of ATP synthase are in 1 of 3 conformations, what are they?

loose, tight, and open

The way the gamma subunit is pointing is always the…

open beta conformation

What does open conformation of a beta subunit mean?

has low affinity for nucleotides, meaning the ATP is going to come off

What does loose conformation of a beta subunit mean?

has affinity for nucleotides - nucleotide will bind to ADP and Pi

What does tight conformation of a beta subunit mean?

has a high affinity for nucleotides and ATP is tightly bound to the beta subunit

When a gamma subunit turns and points a different direction what does that do to beta subunits?

the change conformations

When beta subunits change conformations what does loose become?

tight - so tight it squeezes ADP + Pi to become ATP

When beta subunits change conformations what does tight become?

open

When beta subunits change conformations what does open become?

loose

How do we get cytoplasmic NADH (from glycolysis) into mitochondria?

malate-aspartate shuttle

What occurs in the malate-aspartate shuttle?

• NADH becomes NAD+ - with the opposite reaction: oxaloactetate to malate

• goes through malate-a ketoglutarate transporter

• malate to oxaloacetate reaction happens to make NAD+ to NADH

• for oxaloacetate to go back to cytoplasm takes an amino group and becomes aspartic acid

• gets amino group from glutamate

  • goes out - aspartic acid deaminates to make oxaloacetate and glutamate again

In the malate-aspartate shuttle which molecules can go across the transport proteins?

Malate, a-ketoglutarate; and Aspartate, Glutamate

Per glucose how many ATP’s are made?

32

Per NADH how many ATP’s are made?

2.5 - complex 1

Per FADH how many ATP’s are made?

1.5 - complex 2