cellular metabolism 2
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- Created by: Millie Smith08
- Created on: 17-04-23 14:33
mitochondria
play a key role in aerobic respiration only (oxygen required)
important for the degradation of glucose and fats
the matrix contains the enzymes for the tricarboxylic acid (TCA) cycle
membranes are required for electron transport system
mitochondria also h
important for the degradation of glucose and fats
the matrix contains the enzymes for the tricarboxylic acid (TCA) cycle
membranes are required for electron transport system
mitochondria also h
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pyruvate dehydrogenase complex
controls entry of pyruvate into the TCA cycle
the complex has 3 types of subunit
complex is bigger than a ribosome (although its exact composition depends on the size of the organism)
this complex is not to be confused with pyruvate dehydrogenase, which
the complex has 3 types of subunit
complex is bigger than a ribosome (although its exact composition depends on the size of the organism)
this complex is not to be confused with pyruvate dehydrogenase, which
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pyruvate dehydrogenase (E1)
decarboxylases pyruvate (requires TPP)
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dihydrolipoyl transferase (E2)
makes CoA (requires lipoamide)
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dihydrolipoyl dehydrogenase (E3)
converts reduced lipoamide to disulfide form (requires FAD)
regeneration of co-factors allowing for another cycle to occur
regeneration of co-factors allowing for another cycle to occur
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mammals have
30 x E1, 12 x E2 and 12 x E3
(54 subunits)
(54 subunits)
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thiamine pyrophosphate
TPP (E1)
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lipoamide (disulfide form)
E2
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flavin adenine dinucleotide (FAD)
E3
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cofactors are produced by the enzyme
in this case pyruvate dehydrogenase
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is the rxn reversible?
yes
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thiamine pyrophosphate ylide
ylide means there is a positive and a negative charge next to each other
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lipoamide (disulfide form)
oxidised form
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FAD
oxidised form
used to regenerate lipoamide cofactor
used to regenerate lipoamide cofactor
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FADH2
reduced form
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the pyruvate dehydrogenase complex reaction
1/ TPP anion adds to pyruvate and CO2 is released
2/ lipoamide disulfide is added to acetyl group and a redox rxn occurs
3/ disulfide exchange occurs to form acetyl- CoA and reduced lipoamide
4/ reduced lipoamide is oxidised to disulfide form using FAD
5/
2/ lipoamide disulfide is added to acetyl group and a redox rxn occurs
3/ disulfide exchange occurs to form acetyl- CoA and reduced lipoamide
4/ reduced lipoamide is oxidised to disulfide form using FAD
5/
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the tricarboxylic acid cycle
the cycle is amphibolic (used in both catabolic (degradative) and anabolic reactions
it consists of 8 steps
there are 4 phases:
1/ condensation and rearrangement (steps 1 and 2)
2/ decarboxylation (steps 3 and four- happens twice)
3/ formation of GTP usin
it consists of 8 steps
there are 4 phases:
1/ condensation and rearrangement (steps 1 and 2)
2/ decarboxylation (steps 3 and four- happens twice)
3/ formation of GTP usin
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stage 1
citrate synthase catalyses a condensation of acetyl- CoA and oxaloacetate
hydrolysis of CoA ester makes the rxn irreversible
Citrate undergoes a rearrangement to form isocitrate. This prepares for stage 2
hydrolysis of CoA ester makes the rxn irreversible
Citrate undergoes a rearrangement to form isocitrate. This prepares for stage 2
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stage 2
isocitrate dehydrogenase uses NAD+ to produced a beta-ketoacid
beta-ketoacid spontaneously loses CO2
2-oxoglutarate is converted to succinyl-CoA by a multi-enzyme complex
reaction is analogous to that carried out by pyruvate dehydrogenase (and in fact E2
beta-ketoacid spontaneously loses CO2
2-oxoglutarate is converted to succinyl-CoA by a multi-enzyme complex
reaction is analogous to that carried out by pyruvate dehydrogenase (and in fact E2
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stage 3
CoA is displaced by inorganic phosphate to produced a mixed acid anhydride
produces an ATP equivalent (GTP)
phosphate is transferred to an active site His
transfer of phosphate group onto GDP forms GTP (which can be used to synthesise ATP)
produces an ATP equivalent (GTP)
phosphate is transferred to an active site His
transfer of phosphate group onto GDP forms GTP (which can be used to synthesise ATP)
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stage 4
produces reduced cosubstrates (which can be used to make energy)
converts succinate into oxaloacetate in three steps:
1. desaturation of C-C bond using FAD
2. hydration of double bond. Anti-addition of H2O to obtain S-malate
3. NAD+-dependent oxidation to
converts succinate into oxaloacetate in three steps:
1. desaturation of C-C bond using FAD
2. hydration of double bond. Anti-addition of H2O to obtain S-malate
3. NAD+-dependent oxidation to
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anaplerotic reactions
anaplerotic literally means 'filling up'
the TCA cycle is used to provide starting materials for biosynthesis
this results in depletion of oxaloacetate
acetyl-CoA accumulates
high levels of acetyl-CoA decrease activity of pyruvate dehydrogenase complex (w
the TCA cycle is used to provide starting materials for biosynthesis
this results in depletion of oxaloacetate
acetyl-CoA accumulates
high levels of acetyl-CoA decrease activity of pyruvate dehydrogenase complex (w
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oxidative phosphorylation
takes place in the mitochondria
requires the presence of O2
electrons transferred from NADH and FADH2 (produced by glucose and fatty acid oxidation) to O2 via a series of electron donors
many proteins are inserted into the mitochondrial membrane
consists
requires the presence of O2
electrons transferred from NADH and FADH2 (produced by glucose and fatty acid oxidation) to O2 via a series of electron donors
many proteins are inserted into the mitochondrial membrane
consists
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movement of electrons
energy is related to the electrical potential: ∆G∅=-nF∆E∅
n= no of electrons
F= proportionality constant
electrons can move through a vacuum
speed depends on free-energy change and distance
in proteins it is approx:
- rate constant at van der Waals radius
n= no of electrons
F= proportionality constant
electrons can move through a vacuum
speed depends on free-energy change and distance
in proteins it is approx:
- rate constant at van der Waals radius
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a 1.14 V potential diff exists between NADH and O2
this corresponds to ~220 KJ.mol-1 (cf. ATP hydrolysis = 31.4 KJ.mol-1)
many of these enzymes contain metal centres eg haem
the voltage diff generates a proton gradient (1.4 pH units) (no of protons on both sides not the same)
process is only about 50% ef
many of these enzymes contain metal centres eg haem
the voltage diff generates a proton gradient (1.4 pH units) (no of protons on both sides not the same)
process is only about 50% ef
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chemi-osmotic hypothesis
ATP synthesis is coupled to the proton gradient ('Mitchell hypothesis', 1961) (not quite true)
ATP synthesis consists of:
1- proton transport to mitochondrial inter-membrane space
2- transport of protons through inner membrane by ATP synthase
ATP synthesis consists of:
1- proton transport to mitochondrial inter-membrane space
2- transport of protons through inner membrane by ATP synthase
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is ATP synthesis from ADP and inorganic phosphate spontaneous?
yes
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what is required to drive release of ATP from the enzyme to allow binding of ADP and inorganic phosphate?
a proton gradient (allows for binding of substrate and further rxns to occur)
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stage 1
energy of electron transport used to pump protons across membrane
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stage 2
proton gradient is harnessed by ATP synthase to make ATP
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the FoF1 ATP synthase
head group will rotate driving the release of the products
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Other cards in this set
Card 2
Front
pyruvate dehydrogenase complex
Back
controls entry of pyruvate into the TCA cycle
the complex has 3 types of subunit
complex is bigger than a ribosome (although its exact composition depends on the size of the organism)
this complex is not to be confused with pyruvate dehydrogenase, which
the complex has 3 types of subunit
complex is bigger than a ribosome (although its exact composition depends on the size of the organism)
this complex is not to be confused with pyruvate dehydrogenase, which
Card 3
Front
pyruvate dehydrogenase (E1)
Back
Card 4
Front
dihydrolipoyl transferase (E2)
Back
Card 5
Front
dihydrolipoyl dehydrogenase (E3)
Back
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