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35 Cards in this Set

  • Front
  • Back
the "big picture"
glycolysis converts glu to pyruvate pding 2ATP extracting small amt of energy
w/ O2, pyruvate converted to acetyl-CoA and oxidized to CO2 in citric acid cycle
liberated e's(NADH and FADH2) used in oxidative p-ylation for ATP
the TCA cycle(citric acid,krebs)
aerobic:pyruvate from glycolysis is converted to acetate and degraded to CO2
some ATP is pduced
reducing equivalents(NADH,FADH2) pduced go on to make more ATP by e-transport and oxidative p-ylation
pyruvate dehydrogenase componenets
3 enzymes
oxidative pyruvate
decarboxylate pyruvate
pduces acetyl-CoA
reduce NAD+
TCA cycle components
8 enzymes
oxidize acetyl-CoA
2 decarboxylations
reduce NAD+ and FAD
pduce ATP
the chemical logic of TCA
ways to cleave C-C and oxidize dont work for acetate:
cleavage bw C's alpha and beta to carbonyl
an alpha-cleavage of an alpha-hydroxyketone
chemical logic of TCA
a better way to cleave acetate
condense acetate with oxaloacetate and do beta cleavage
TCA with oxidation to get CO2 regenerate oxaloacetate and capture all the energy as NADH and ATP
entry into the TCA cycle
(link bw glycolysis(cytosol) and TCA(mitochondria)
pyruvate dehydrogenase (PD) and citrate synthase
PD complex (PDC)
1.pyruvate is oxidatively decarboxylated to acetyl-CoA
2.complex has 3 enzymes:
b.dihydrolipoyl transacetylase (DTA)
c." " dehydrogenase (DLD)
PDC uses 5 enzymes
thiamine pyrophosphate
lipoic acid
pyruvate dehydrogenase enzyme complex
24 DTA subunits=cubic core(pink)
24 alphabeta dimers of PD (2 per edge, yellow)
12 DLD (2 per face, blue)
reaction mechanism of pyruvate dehydrogenase complex
1.pyruvate loses CO2 and HETPP is formed
2.hydroxyethyl is transferred to lipoic acid and oxidized to form acetyl dihydrolipoamide.
3.aceytl is transferred to CoA
citrate synthase
first rxn within the cycle
acetyl-CoA provides 2C to oxaloacetate in condensation rxn to pduce citrate
big - delta G
inhibitors:NAD and succinyl-CoA (pdts of TCA)
citrate synthase rxn
entering the TCA cycle condensing AcCoA with 2C and OAA with 4C resulting in 6C with the chiral C on top (S arm)
isomerization of citrate to isocitrate
citrate is poor substrate for oxidation
aconitase isomerizes citrate to yield isocitrate that has secondary -OH, that can be oxidized
(aconitase removes the pro-R H of the pro-R arm of citrate)
isocitrate dehydrogenase
oxidative decarboxylation of isocitrate to yield alpha-ketoglutarate
a hydride removal
ID is a link in the e-transport bc it makes NADH(made ATP in e-transport)
inhibitors:NADH and ATP
isocitrate dehydrogenase reaction
two step rxn
oxalosuccinate intermediate is unstable and readily decarboxylates
alpha-ketoglutarate dehydrogenase
(a 2nd oxidative decarboxylation)
enzyme identical to PD
five coenzymes used:
TPP,CoASH,lipoic acid,NAD+,FAD
alphat-ketoglutarate dehydrogenase rxn
alpha-ketoglutarate by dehydrogenase to succinyl-CoA
high - delta G
NADH and succ-CoA are energy rich pdts
succinyl-CoA synthetase
substrate level p-ylation
nucleoSide tri-P is made
synthesis driven by hydrolysis of a CoA ester
succinyl-CoA synthetase rxn
succinyl-CoA by synthetase to succinate
get GTP + CoA from intermediate
whats happened in TCA cycle so far....
2C acetyl introduced
2CO2 liberated
NADH pduced
GTP into ATP(mammals) or ATP pduced
to complete cycle succinate must be oxidized to oxaloacetate involving:
oxidation step
hydration rxn
2nd oxidation step
succinate dehydrogenase
(an oxidation involving FAD)
hydride removal by FAD and deprotonation
enzyme is part of e- in the inner mito mem
e's transferred from succinate to FAD are passed to biquinone in the e path
succinate dehydrogenase rxn
succinate by dehydrogenase to fumarate
hydration across a =
transaddition of elements of water across the =
fumarate by fumarase to L-malate
malate dehydrogenase
(an NAD+ dependent oxidation)
C that gets oxidized is the one that receiveed the -OH in the previous rxn
energetically expensive (+G)
malate dehydrogenase rxn
L-malate by dehydrogenase to oxaloacetate
fate of carbon in TCA
C of acetyl have diff fates:
carboxy C:is in CO2 only 2nd turn of cycle
methyl C:survives 2 complete cycles but half of whats left exits the cycle on each turn after that.
intermediates for biosynthesis
(TCA also provides intermediates)
a-ketoglutarate:transaminated to make glutamate, used to make purine nucleos Arg & Pro
succinyl-CoA:makes porphyrins
fumarate and oxaloacetate:used to make aa and pyrimidine nucleotides
the anaplerotic rxns
("filling up" rxns of TCA)
pyruvate carboxylase:(animal mitos)most important, convert pyruvate to oxaloacetate(rxn adds CO2)
PEP carboxylase(not in animals):PEP to oxaloacetate
malic enzyme:converts pyruvate to malate
more anaplerotic rxns
PEP carboxykinase:could be, but goes wrong way(CO2 binds weak and oxaloacetate binds strong)
anaplerotic rxns replace TCA intermediates "lost" to other pathways
PEP carboxykinase
wrong way rxn
favors PEP formation over oxaloacetate
regulation of TCA
(3 rxns are key sites...?)
citrate synthesis:ATP,NADH,succ-CoA inhibit
isocitrate dehydrogenase:ATP(inhibit), ADP & NAD+ (activate)
a-ketoglutarate DH:NADH,succ-CoA (inhibit), AMP (activates)
Glyoxylate cycle rxn
pyruvate DH is highly regulated by phosphorylation
conversion of pyruvate to acetyl-CoA
varient TCA for plants and bacteria
rxns occur in glyoxysomes(specialized organelles in plants devoted to this cycle)
glyoxylate cycle
acetate based growth:net CHO and other intermediate
soln for higher plants,algae
CO2 evolving steps are bypassed
isocitrate lyase and malate synthase are short-circuiting enzymes
glyoxylate cycle II
isocitrate lyase pduces glyoxylate and succinate
malate synthase:condensation of acetyl-CoA and aldehyde of glyoxylate
glyoxylate helps plants grow in the dark
glyoxysomes borrow 3 rxns from mito:succ to oxaloacetate
glyxysome lacks 3 enzymes required
succ DH, fumarease,malate DH
borrow enzymes from mito
succ & glutamate passed to mito
a-ketogluterate and aspartate passed from mito to glyoxysome