Fatty acids breakdown and synthesis and photosynthesis
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Cours
Biochemistry (BIO1332)
Établissement
University Of Exeter (UoEX)
Book
Biochemistry
A summary of the lectures on fatty acids and photosynthesis. Explaining both fatty acid beta-oxidation and synthesis and fatty acid properties.
Also covers photosynthesis and the Calvin Cycle.
Metabolisme & Biochemie werkcollege en self-test antwoorden voor H 1, 2, 7, 8, 9 en 11
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University of Exeter (UoEX)
University of Exeter
Biochemistry (BIO1332)
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Functions: Glyoxylate cycle – making sugars from fatty acids (plants, fungi)
- Energy storage and production Occurs in glyoxylomes. Isocitrate lyase and malate synthase allow the
- Structural components of bypassing of the citric acid decarboxylations, so they keep the 2 carbons
membranes put in. 2 acetyl CoA -> malate -> oxaloacetate. Two oxaloacetates ->
- Some hormones are derived from glucose (gluconeogenesis)
fatty acids & have roles in Exception – odd chain length fatty acids yield acetyl CoA and propionyl CoA
inflammation, bp regulation etc. from β oxidation. The C3 propionyl CoA can be carboxylated to D-
Saturated fatty acid = no double bond methylmalonyl-CoA (biotin cofactor), which is isomerised to its L form , and
Usually have an even no. of carbons then rearranged by vitamin B12 to succinyl CoA. Succinyl CoA can be used
as synthesised from C2 precursor to make glucose from the citric acid cycle (2 molecules needed), as it
(acetyl CoA) occurs after the decarboxylation reactions.
Note: fats are only used when glucose
supplies are low: Fatty acid synthesis
TAG + 3H2O -> glycerol + 3 fatty acids Occurs in the cytoplasm. Substrates = acetyl CoA (delivered by citrate
But the brain cannot oxidise fatty shuttle from mitochondria) + NADPH (from pentose phosphate pathway).
acids for energy, only glucose. Process is similar to the reverse of breakdown, but it uses a different
TAG breakdown catalysed by carrier (ACP), has NADP+ as the cofactor and malonyl CoA is the C2 donor.
triacylglycerol lipase – activated
Both processes
glucagon are reciprocally
regulated
Oxidation of fatty acids
Step 1) Fatty acid activation –
formation of acyl CoA in cytoplasm
-Fatty acid reacts with ATP, liberates
2Pi (bonded), fatty acid group bonds
to AMP (ester bond), but then the
AMP is displaced by a thiol bonded
CoA to get Acyl CoA + AMP. Step 1: acetyl group added using
Activation costs 2 ATPs Fatty acids malonyl CoA as the donor, loss of CO2
(AMP + ATP = 2 ADP) drives the reaction. (malonyl
Step 3: oxidation of fatty acids in synthesised by carboxylation of acetyl
Step 2: Fatty acyl CoA uptake by mitochondria CoA using ATP and acetyl CoA
mitochondria 1- H removed from α & β carboxylase (biotin cofactor).
Fatty acids taken into mitochondria carbons by acyl CoA Step 2: C=O on C3 reduced to C-OH
by carnitine shuttle as inner dehydrogenase – by NADPH
mitochondrial membrane not contains FAD cofactor. Step 3: dehydration generates a
permeable to fatty acids. Shuttle : Electrons delivered to double bond between α and β
fatty acyl CoA reacts with carnitine ( + coenzyme Q in ETC (1.5 carbons
free CoA), moves through exchanger ATP) Step 4: reduction of double bond to
– fatty acyl carnitine in, carnitine out. 2- Hydration of double bond single bond using NADPH.
Inside the mitochondria, fatty acyl (addition of H20) to give Fatty acid is 2C longer, can undergo
carnitine + CoA form carnitine (which hydroxyacyl CoA process again or the process can be
then leaves in the exchanger) and 3- C-OH oxidised to C=O. stopped by removing ACP using fatty
fatty acyl CoA. NADH formed then acyl-ACP thioesterase.
Carnitine palmitoyl transferase I is oxidised in ETC (2.5 ATP)
inhibited when the cell is trying to 4- β-ketoacyl-CoA Fatty acid synthase (FAS)
make fatty acids. undergoes thiolysis via A single, multifunctional enzyme,
CoASH which attacks β which exists as a dimer and makes
carbon to form acetyl fatty acid synthesis more efficient as
CoA and a fatty acyl CoA 2 all the enzymes needed are in one
carbons shorter than it place.
started off as. Acetyl CoA carboxylase – inhibited
This repeats until the whole thing by phosphorylation, activated by
is converted into acetyl CoA. You phosphatase (activated e.g by
get 10 ATP per acetyl CoA + those insulin)
from NADH and FADH2
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