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Biochem Muscle Weakness ATP 1


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Explain PDH
(eqn) what does it do
Pyruvate dehydrogenase:
pyruvate + NAD + CoA -->
Acetyl~CoA + NADH + H + CO2

it is a multienzyme complex: this allows the efficient transfer of intermediates b/w active sites, interm usually cov linked to enz
PDH cont'd
name the catalytic cofactor
name the stoichiometric cofactor
catalytic cofactor: coenz-prosthetic group FAD TPP(thiamine pyrophosphate) and lipoic acid)

Stoichiometric cofactor: coenz-cosubstrate - NAD CoA

2 stoichiometric coenz-cosubstrates (NAD CoA)
3 coenzy prosthetic groups
3 distinct enz
2 other enz regulate activity of PDH complex
where does PDH cycle occur?
in the mitochondrial matrix
what does PDH do in a general sense
converts pyruvate from cytosol into Acetyl CoA for entry into TCA cycle
explain, using the different enz's of PDH, how it converts pyruvate into Acetyl CoA
pyruvate is decarboxylated by TPP in E1
oxidation by lipoic acid in E2(causing transfer of acetyl group to CoA)
reoxidation of lipoic acid by FAD (b/cms FADH)
FADH is then converted back to FAD via 2NAD
in PDH, give the names for E1 E2 and E3
E1: pyruvate dehydrogenase(pyruvate decarboxylase)
E2: dihydrolipoyl transacetylase
(lysine chain acts as a swinging arm to transfer e from E1 to E3)

E3: dihydrolipoyl dehydrogenase

In PDH deficiency, why is lacticacidemia an expected finding?
Control of PDH
very important
explain covalent regulation
most important: inhibition through phosphorylation of E1

Covalent regulation:

stim by ATP(uses it) NADH and AcetylCoa
inhib by pyruvate

Phosphatase: ACTIVATES
activated by Ca (Ca released when ATP is utilized) therefore PDH is upregulated in response to energy deprivation
name two ways acetylCoA is produced
PDH and beta-oxidation of fatty acids
anaplerotic reactions
rxns that generate TCA intermediates outside of the TCA cycle itself, this is necessary b/c most of the enzymes are free floating in the matrix space and can be used up in other pathways
explain the initiating step in the TCA cycle and what makes it irreversible
citrate synthase catalyzes the condensation of acetylCoA with oxaloacetate to form citrate

hydrolysis of the thioester bond of CoA makes it irreversible!
Which steps in TCA produce NADh/FADH2
3 produce NADH, IDH alpha-ketoglutarate dehydrogenase, malate dehydrogenase
1 produces FADH2, succinate dehydrogenase
list the names of the TCA cycle intermediates in order
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succinyl CoA
what enzyme is embedded in the inner mitochondrial membrane?
succinate dehydrogenase
what is the name of reactions that generate TCA cycle intermediates from outside the cycle itself?
anaplerotic reactions
what, besides hydrolysis of thioester bond of CoA is important about the initiating step?
enzyme-bound intermediate is formed. Citrate synthase

Free state, citrate synthase binds oxaloacetate first causes a change and then binds acetyl CoA so that Acetyl CoA isnt wasted by changing into citric acid
what other reactions form enz-intermediates
aconitase enz forms cis-aconitate before forming isocitrate
explain competitive product inhibition of PDH
acetyl CoA competitively inhibits E2(binds active site?)
NADH competitively inhibits E3
citrate to isocitrate through cis-aconitase

relocation of OH prepares it for IDH
isocitrate dehydrogenase
isocitrate to alpha-ketoglutarate through the intermediate oxalosuccinate

forms NADH and CO2
alpha-ketoglutarate dehydrogenase
alpha-ketoglutarate to succinyl CoA
produces CO2 using CoASH
produces NADH
Succinyl CoA synthetase (Succinyl Thiokinase)
reversible? pg 390

succinyl CoA-> Succinate

produces coash from Pi
makes GTP

COUPLING - GTP production is coupled to the high energy bond in succinyl coa made previously from alpha keto glutarate, succinyl CoA is the intermediate

Succinyl CoA -> succinyl phosphate -> succinate

it's succinyl phosphate to succinate that generates GTP, so succinyl phosphate is the intermediate in that reaction
where does most of the respiratory CO2 come from?
IDH alpha KDH and PDH

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