Metabolism - Lec 5 Flashcards
what happens to pyruvate before entering the TCA cycle ?
Pyruvate dehydrogenase is the enzyme
pyruvate is converted using coenzyme A (CoA)
to acetyl CoA
NAD+ to NADH + H+
CO2 is released
happens in the mitochondrial matrix
reaction is irreversible, so hence a key regulatory step
PDH is a large (5) multienzyme complex, requires many cofactors , B vitamins provide this
so reaction is sensitve to vitamin b1 deficiency
what is caused by a PDH deficiency ?
Lactic Acidosis
what affects PDH
PDH is activated by low energy signals - NAD+, ADP , Insulin, Pyuvate
inhibited by high energy signals - Acteyl CoA, NADH, ATP, Citrate
Acetyl CoA feeds into the Tricarboxylic acid cycle (TCA or Krebs cycle)
summarise the TCA cycle
it is mitochondrial
central pathway for metabolism of sugars, fatty acids, amino acid, ketone bodies, alcohol
requires O2 to function
the intermediated act cataltically
Oxidative - requires NAD+, FAD
produces GTP (energy)
Proudces precursors for biosynthesis - fatty acids from citrate, amino acids, haems
oxaloacetate (C4) can be a source of glucose in starvation
Acetyl CoA is converted to 2 CO2 which is released
explain the TCA cycle
draw if possible
pyruvate —-> Acetyl CoA (C2)
Acetyl CoA (C2) adds to C4 —–> Citrate (C6)
citrate is converted to isocitrate (C6)
isocitrate oxidised to C5
1 NAD+ to NADH occurs
C5 to C4 oxidiation, assisted by CoA
1 NAD+ to NADH occurs
GDP —-> GTP with CoA leaving again
FAD —-> FADH2 occurs
additoin of H2O
NAD+ to NADH reduction occurs
C4 is produced that joins with acetyl CoA
total products are
3x NADH
1x GTP
1x FADH2
be aware this cycles twice for every glucose molecule
so 6x, 2x and 2x
what are key enzymes involved in regulation of the TCA cycle ?
Isocitrate dehydrogenase isocitrate to C5 - NADH and CO2 produced
Stimulated by ADP - low energy signal
Inhibited by NADH and ATP - high energy signals
a-ketoglutarate dehydrogenase - inhibited by NADH, ATP, succinyl CoA (next intermediate) - high energy signals
All of the NADH and FADH2 bond energy now created from glycolysis, is used to drive ATP synthesis
so far we have produced
2 NADH from glycolysis
2 from Pyruvate Dehydrogenase
6 from the krebs cycle
2 FADH2 from the krebs cycle
this is now ready for stage 4 , summarise it
it is mitochondrial
it is electron transport and atp synthesis
NADH and FADH2 are re oxidised
O2 is required and H2O is produced
Lots of ATP produced - oxidative phosphorylation
explain how the structure of a mitochondrion is designed for ATP synthesis
have and outer leaky membrane
inner membrane that is highly impermeable and made of cristae (to increase SA)
matrix is inside and inter membrane space is the gap between the two membranes
how does mitochondrial electron transport work ?
NADH is oxidised releasing NAD+
a proton tranlocating complex pushes 2H+ across to the intermembrane space
2e- drops between up to 3 PTC’s pushing 6 H+ across for 1 NADH oxidaiton
the 2e- afeter dropping through the PTC’s releasing its enrgy, joins with O2 and 2H+ to produce H2O
this is the creation of a proton gradient
H+ are built up in the intermembrane space by the proton translocating complex’s, negative internal charge
30% of the energy is used in moving the H+ across the membrane - this is energy released as heat
the H+ gradient is called the proton motive force (pmf)
what does proton translocating ATPase do ?
the reaction -
ATP +2H+ (mitochondrial matrix) ADP + Pi + 2H+
the 2 H+ molecules are pushed across the membrane, the energy released is used to synthesise ATP from ADP + Pi
this ATP synthase molecules is pushing H+ molecules back into the inner membrane space, using the H+ gradient (pmf) created by the PTC complexes
the return of protons is energetically favoured by a electrical and chemical gradient
protons can only return across the membrane via the ATP synthase protein, driving ATP sysnthesis
Did you get the concepts right ? pure accuracy is not needed
summarise the process of oxidation phosphorylation in the mitochondria
electrons transferred from NAH and FADH2 to molecular oxygen
Energy released used to generate a proton gradient - proton motive force PMF
energy from dissapation of PMF via ATP synthase is used to synthesise ATP from ADP
H2O is a released product
NADH electrons are higher energy than FADH2 electrons - produce more ATP per molcule
NADH - 3 PTC’s - 2 moles NADH produces 5 moles ATP
FADH2 - 2 PTC’s - 2 moles FADH2 produces 3 moles ATP
32 moles total ATP are produced from 1 mole of glucose
how is oxidative phosphporylation regulated ?
if ATP is high, ADP is low - there is no substrate for ATPsynthase to use
the flow of H+ inwards stops
amount of H+ in intermitochondrial space increases
this prevents further H+ pumping out - stopping electron transport
how is oxidative phosphorylation inhibited ?
inhibitors such as Cyanide and carbon monoxide block electron transport by stopping electron oxygen acceptance
No pmf genrated
H+ cannot flow down electrochemical gradient via ATPsynthase, and no ATP is porduced - we die
what are the roles of uncouplers in oxidative phosphorylation ?
uncouplers such as poisonous dinitrophenyl increase the permeability of the inner mitochondrial membrane to H+
this dissipates the proton gradient
reducing the PMF
no drive for ATP synthesis
what are ox/phos diseases ?
Genetic defects in proteins for PTC and ATP systhase
Less elecron transport - Less ATP production - Lower energy levels
