Unit 19: TCA/Citric acid/ Krebs cycle; PDH rxn; Beta oxidation Flashcards
describe mitochondria generally
- where energy conversion happens
- Hundreds to thousands per cell , depending
on cell type
– Many fused to one another
– Some cells do not have mitochondria - has a Double membrane
– Outer membrane controls entry of
large molecules
– Electron transport chain (ETC) and ATP synthesis enzymes located in inner membrane - need over 1000 different proteins for maintenance and function
- most are encoded by nuclear genome and imported. some are encoded by mtDNA
describe mitochondria inner membrane
- High content of cardiolipin and very protein-rich
- Impermeable to ions and small charged molecules
- Contains electron transport chain (ETC) and ATP Synthase
- Contains protein importers (e.g., TIM), transporters and shuttles for small molecules and ions
describe mitochondria Outer membrane
- Molecular sieve with channels formed by porins
- Permeable for molecules < 5 kDa (in open state)
- Enzymes for mitochondrial lipid synthesis located here
- Import receptors and translocases for proteins (TOM complex) here
describe mitochondria Intermembrane space
- Similar to cytoplasm in composition (small molecules)
- Various enzymes exist here
- the space between the outer membrane and inner membrane
describe mitochondria Matrix
Contains enzymes for several pathways
- pyruvate oxidation, TCA, amino acids, fatty acids, etc.
Contains mtDNA, transcription and translation components
- inner most compartment
the TCA is the complete oxidation of fuel carbon backbone to CO2 with ____
electrons bound to carriers
Acetyl CoA (C2) is also know as
activated acetate
what is the first molecule to enter the TCA cycle
acetyl CoA
what are the catabolic and anabolic functions of TCA cycle
Catabolic:
- Provides electrons for oxidative phosphorylation
(3 NADH and 1 FADH2 per full cycle)
- Provides energy via substrate- level phosphorylation (1 step, 1 GTP)
anabolic:
- Provides precursors for building blocks
is the TCA cycle Amphibolic?
yes, has both catabolic and amphibolic pathways
what coupled cycles provide most of the energy from glucose oxidation
the TCA cycle and oxidative phosphorylation (ETC + ATP synthase)
do Fatty acids, glucose and Amino acids all feed into the TCA cycle?
yes, via acetyl coA
describe the PDH reaction
- pyruvate transported into mitochondria matrix via mitochondrial pyruvate carrier (MPC)
- Oxidative decarboxylation to acetyl CoA by PDH enzyme complex in the matrix
- irreversible rxn
what is the net reaction of the PDH rxn
pyruvate + CoA + NAD = Acetyl CoA + CO2 + NADH + H+
what is the ∆𝐺′° of the PDH rxn
-8.0 kcal/mol
what is the PDH complex made of
E1: Pyruvate dehydrogenase (TPP)
E2: Dihydrolipoyl transacetylase (Lipoamide) + CoA
E3: Dihydrolipoyl dehydrogenase (FAD) + NAD+
what are the 5 coenzymes of the complex
TPP,
Lipoamide + CoA,
FAD + NAD+
what are the co-substrates of the PDH rxn?
CoA and NAD+
- they are not tightly bound. they pick up molecules and leave
what are the prostethic groups of the PDH rxn
TPP (Pyruvate dehydrogenase) (E1)
Lipoamide (Dihydrolipoyl transacetylase) (E2)
FAD - dihydrolipoyl dehydrogenase (E3)
what are the apoenzymes of the PDH rxn
Pyruvate dehydrogenase
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase
what does Pyruvate dehydrogenase do
takes away the CO2 and electrons
what does Dihydrolipoyl transacetylase do
something with the acetyl
what does Dihydrolipoyl dehydrogenase do
take the electrons away
describe general mechanism of PDH rxn
pyruvate decarboxylase
1. decarboxylation of Pyruvate
2. oxidation of acetyl group w/ simultaneous transfer to lkpoamide + formation of thioester bond
Dihydrolipoyl transacetylase
3. transfer of acetyl group from lipoamide to CoA + Preserves thioester bond
Dihydrolipoyl dehydrogenase
4. regeneration of lipoamide by oxidation of dihydrolipoamide
– Prosthetic FAD group as primary electron acceptor
– Electrons then transferred to NAD+
