BCH210 Lecture 19, 20, 21 (oxidative phosphorylation)

lecture 19

what is the 1st law of thermodynamics

energy cannot be created nor destroyed

how does oxidative phosphorylation apply to the 1st law of thermodynamics

as electrons are passed from carrier to carrier a change in redox potential gnerates free energy- this is used to power a conformational change in the protein complexes and pumping protons from the matrix into the inter membrane space- proton gradient is then used by ATP synthase to make ATP in the matrix

what is standard reduction potential (E’ 0)

a molecules tendency to be oxidized or reduced

-E → looses electrons more (oxidized)

+E → gains electrons more (redox)

what is the formula for standard reduction potential

G = -nFE

where G would need to be + to be favorable bc negative sign on other side

n= # electrons

F= faraday constant 96485 J/Vmol

E = delta (use number line to find differernce) 

how does ATP synthase make ATP from the proton gradient

electrochemical gradient across the mitochondrial inner membrane

• proton gradient produced by electron transport using suitable electron donors

• proton motive force is the driving force behind ADP to ATP conversion

what does ATP synthase do

• ATP synthase is membrane bound, reversible and dependent on the proton gradient 

• F1 carries out the catalytic synthesis of ATP in the matrix and F0 is the inegral membrane protein unit and anchors the complex to the membrane

  • binding od H+ in the rotor causes a rotation in the ring of C subunits of F0

  • this rotation rotates the y subunit inducing conformational changes in the b subunits and H+ are released into the matrix

  • conformational changes in the F1 b subunits are responsible for ATP synthesis

what are the three states of the b subunit of ATP synthase

open - ATP leaves

loose- ADP and Pi bound

tight - ATP bound 

what are the oxidative phosphorylation inhibitors

• rotenone and amytal : inhibit electron flow from complex I to CoQ (turn off complex 1)

• antimycin A: blocks complex 3

• cyanide, azide and Co: inhibit complex 4

• oligomycin: inhibits ATP synthase (complex 5)

• uncouplers: disrupt the H gradient affecting atp synthesis

  • protons get pumped across then brought back by uncouplers 

what are uncouplers

amphipathic molecules that can cross the membrane, they contain acid groups that can be protonated/deportonated depending on the side of the membrane pH (the matrix is more basic therefore deprotonated, and the cytosol is more acidic therefore protnated)

this allows them to bind H and move them from high to low concentration, disrupting the proton gradient and ATP synthesis 

how many H are needed for ATP synthesis

4 H per

• 3H per 1 ATP produced

• 1 extra H is needed for ATP export and ADP and Pi import to maintain charge across inner mitochondrial membrane 

what are the p/o ratios per NADH atp synthesis

NADH = 2.5 (2)

• NADH pumps ~10 protons (H⁺) across the inner mitochondrial membrane

  • Complex I pumps 4 H⁺

  • Complex III pumps 4 H⁺

  • Complex IV pumps 2 H⁺
    Total = 10 H⁺ per NADH oxidized

• ATP synthase requires ~4 protons to make 1 ATP

  • 3 H⁺ flow through ATP synthase to rotate the enzyme and synthesize ATP

  • + 1 H⁺ is needed to transport inorganic phosphate (Pi) into the matrix
    → Total = 4 H⁺ per ATP

• So the ATP yield from NADH is: 2.5 

what are the p/o ratios per FADH atp synthesis

• Complex II: 0 H⁺

• Complex III: 4 H⁺

• Complex IV: 2 H⁺
  Total = 6 H⁺ per FADH₂

ATP calculationFADH2=6 H+4 H+/ATP=1.5 ATP\text{FADH}_2 = \frac{6\ \text{H}^+}{4\ \text{H}^+/\text{ATP}} = 1.5\ \text{ATP}FADH2​=4 H+/ATP6 H+​=1.5 ATP

what is the water ratios for oxidative phosphorylation

it is the same as atp + 1 because there is. 1h20 formed in the last step of electron transfer in complex 5

NADH → 3.5

FADH → 2.5 

what is the overall equation fro complete glycose oxidation

1 glucose + 30 ADP + 30 Pi + 6O2 → 6 CO2 +30 ATP +36 H2O

where are extra carbons stored

in triglycerides

explain the strucutre of triaclyglycerol

acyl chains connected by glycerol backbone via ester bonds

3 fatty acyl chains are saturated to allow for close packing

chains must be hydolyzed off for use 

how are free fatty acids made and how are they transported

lipases hydrolyze ester bonds of triglycerides to produce FFA and glycerol

FFA are transprted in the blood via albumin for cellular use 

explain fat mobilization via GPCR signalling

1. epinephrine and glucagon bind to GPCR on adipose cells

2. Ga-GTP is released, adenyly cyclase and cAMP production lead to PKA activstion which initates a signal

3. PKA phosphorylates and activates triacylglycerol lipase (HSL) and TAGs are hydolyzed to 3 FA + glycerol that are released in the blood and transported via albumin 

acyl CoA vs acetyl CoA

acyl → 2 carbons attached to CoA

acetyl → larger carbon chain 

how is FA activated in the cytoplasm and why is this rxn favourable

acyl coa synthetase catalyzes a reversible reactions that uses ATP → AMP + PPi to form the acyl coa molecule 

its favourable due to the hydrolysis of ATP, where water and pyrophosphate (PPI) become two inorganic phosphate molecules (2Pi).

what must be done to make ATP from AMP

AMP must be converted to ADP by using another ATP

AMP + ATP (adenylate kinase → ) 2 ADP (ATP synthase →) 2 ATP

what does FA activation by CoA require

2 ATP (1 for activation and 1 for production of ADP) and 1 H2O (to hydrolyze PPi)

where is acyl coa made and where does b-oxydation occur, why are these different

acyl coa is made in the cytoplasm

b-oxidation occurs in the matrix

because fatty acids are activated in the cytosol before they can be transported into mitochondria for beta-oxidation. The activation process involves attaching coenzyme A to a fatty acid, forming acyl CoA. This reaction is catalyzed by acyl-CoA synthetase

how does acyl coa get into the matrix

the carnitine shuttle regulates what comes into the mitochondria

CAT I (carnitine acyltransferase) moves the acyl chain onto carnitine from coa

carnitine acyltransferase II (CAT II) moves acyl chain back onto coa (in matrix)

NOTE: the translocase is an antiporter moving FA chains in and carnitine out 

what is the formula for rounds of beta oxidation

n/2 -1, where n is number of carbons

e.g. to break down 16:O coa, 7 rounds of b oxidation are needed (16/2-1) (bc each coa has 2 carbons)

what is the formula for b oxydation prod and substrates

#:0 CoA + (n/2-1) NAD+ + (n/2-1) FAD + (n/2-1) H2O + (n/2-1) CoA →

n/2 + (n/2-1) NADH + (n/2-1) FADH2 + (n/2-1) H+

what is TCA dependent on

amount oc oxaloacetate present → to make ATP from fat efficiently at least

what is oxaloacetate made from

amino acids or pyruvate by pyruvate carboylase (GNG)

what is the hormone needed for cellular uptake of fuel

insulin

what are the steps in FA synthesis

1. expor of mitochondrial acetly coa to the cytoplasm for fat synthesis

2. carboxylation of acetly coa to malonyl coa by acetyl coa carboxylase (ACC)

3. use of malonyl coa to form 16:0 FA chains by FA synthase

how does acetly coa cross the membrane

citrate synthase makes citrate in the CAS which can cross the inner membrane, then be broken down into different enzymes to recreate acetyl coa and regenerating a pyruvate

the pyruvate can return to the mitochondria while acetyl coa is used for synthesis of fatty acyl chains in the cytoplasm 

what two enzymes are needed for FA synthesis

1. acetly CoA carboxylase (ACC)

2. fatty acid synthase

what does ACC do

converts acetly coa to malonyl coa

what is malonyl coa

an activated 2-carbon carrying precursor for FA synthesis

what is the regulated step of FA synthesis

ACC

how are ACC and FA synthase powered

ACC uses ATP

FAS uses NADPH

how does malonyl coa drive FA synthesis

it has a CO2 group that can be used by FAS

how is the carnitine shuttle regulated for import of chains

the product of ACC (malonyl coa) inhibits CATI

explain how ACC is regulated via phosphorylation