fatty acids Flashcards
fatty acids
- energy storage and production
- structural components of membranes
- some hormones are derived from fatty acids
lipids
fatty acidsare conjugated with glycerol to form lipids -3 fatty acids linked to glycerol by an ester bond
lipids are..
highly hydrophobic and not easily transporte
TAG
triacylglycerol
TAG as an energy source
not used until glucose supplies are low
-broken down in adipose tissue (fat tissue) is catalysed by triacylglycerol lipase
TAG + 3H2O –> glycerol and 3 fatty acids
-fatty acids are transported into the blood stream with albumin
what catalysis the break down of TAG
triacylglycerol lipase
what activates lipase
hormonally activated by glucagon
saturated fatty acids
no double bonds
unsaturated fatty acids
contains one or more double bonds (of cis configurations )
fatty acids usually have an ….. number of C atoms
even
what are fatty acids synthesised from
C2 precursor: acetyl CoA
oxidation of fatty acids (3)
step 1: free fatty acids in the cytosol are activated formation fatty acylCoA step 2: fatty acyl-CoA uptake into mitochondria Step 3: beta-oxidation pathway in mitochondria
only organ in the body than cannot use fat as an energy source
the brain
step 1 of oxidation of fatty acids
-fatty acid activation- formation of any; CoA in cytoplasm -costs the equivalent of 2ATPs -AMP +ATP= 2 ADP
step2 of oxidation of fatty acids
fatty acyl CoA uptake by mitochondria - in animals, fatty acids are oxidised in mitochondria -the inner mitochondrial membrane is not permeable to fatty acids ro fatty acyl CoA and instead the carnitine shuttle is used to transport fatty acyl CoA from the cytoplasm to the mitochondrial matrix
carnitine shuttle
transports fatty acyl CoA from the cytoplasm to the mitochondrial matrix
step 3 of oxidation of fatty acids
Beta oxidation of fatty acids in mitochondria - called B oxidation because the B carbon (C3) is oxidised 1.H removed from alpha and B carbons by acyl CoA dehydrogenase. Contains FAD cofactor. Electrons delivered to Coenzyme Q in ETC 2. Hydration of double bond- to produce hydroxyacly-CoA 3. C-OH oxidised to C=O. NADH formed is oxidised by ETC to produce ATP 4. CoASH attacks B carbon (red) to produced acetyl CoA and a fatty acyl CoA which is now 2 C atoms shorter Acetyl Co A oxidised by citric acid cycle
in a even chained fatty acid (oxidation)..
all molecules are converted into acetyl CoA
ATP yield from oxidation of palmitate
16 carbons long -cost of activation to palmitoyl-CoA= 2 ATP -7 rounds of b-oxidation -8 acetyl coA -8 x 10 ATP=80 ATP 7NADH -7x 2.5 ATP=17.5 ATP
what can convert fatty acids to sugars and what cant
animals can convert fats to sugars and animals cannot
plants and fungi can convert acetyl CoA into
sugars- because they have the glyoxylate acid cycle
glyoxylate cycle
occurs in specilsiased organelles called glyoxysomes
overall reaction in glyoxyate cycle
2Acetyl CoA–> malate–> oxaloacetate
oxaloacetate can then be used to produce glucose vi
glucoseneogenesis
odds chain fatty acids yield..
ATO and propionyl CoA
although animal are incapable of producing glucose from acetyl CoA.. they can..
make glucose from propionyl CoA
mammals can produce glucose from
odd chain fatty acids
Fatty acid synthesis: first step
energy to form C-C bonds is supplied indirectly by synthesising malonyl CoA from acetyl CoA using AT and CO2 - reaction is catalysed by Acetyl CoA carboxylase (uses biotin as a cofactor)
what cofactor does acetyl co A carboxylase use
biotin
Step 1 of biosynthesis
an acetyl (2C) group is added using Malonyl CoA as the donor. Loss of CO2 drives the reaction Malonyl CoA s synthesised by the carboxylation of acetyl CoA Acetyl CoA + CO2 + ATP malonyl CoA +ADP + Pi
Step 2 of biosynthesis
the C=O group on the C3 (B carbon) is reduced to C-OH by NADPH
step 3 of biosynthesis
dehydration generates a duble and between the alpha and beta carbons (C2 and C3)
step4 of biosynthesis
reduction of double bond to single bond
step 5 biosynthesis
fatty acyle-ACP, now 2C longer, can re-enter the process or the process is stopped by removing ACP (using fatty acyl-ACP thioesterase)
what removes ACP and stops fatty acid synthesis
fatty acyl-ACP thiesterase
basics on fatty acid synthesis
same intermediates as B oxidation -occurs in cytosol different carrier (acyl carrier protein instead of acetyl CoA) -diff cofactors
substrates of synthesis of fatty acids
acetyl CoA and NADPH
citrate shuttle
used to transport acetyl CoA from the mitochondria to the cytoplasm
sources of NADPH for fatty acid synthesis
pentose phosphate pathway and the citrate shuttle
acetyl CoA carboxylase
is a biotin-dependent enzyme that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA
acetyl CoA carboxylase is tightly regulated
inhibited by phosphorylation- AMP kinases is one of the major kinases–> others are controlled by glucagon and adrenaline
insulin signalling favours…
fatty acid synthesis by activating phosphatase that dephosphorylates acetyl CoA carboxylase.
what is reciprocally regulated
fatty acid synthesis and breakdown
glucagon promotes
release of fatty acids from ADIPOCYTES- high levels of fatty acyl CoA inhibits acetyl CoA carbboxylase
malonylCoA made by acetyl CoA carboxylase inhibits..
carnitine acyle transferase I and prevents fatty acid oxidation by blocking entry into the mitochondrion
summary of fatty acids
Summary
♣ Lipids have a range of functions- cell membrane, energy storage and cell signalling
♣ Fatty acid degradation (b-oxidation) occur in the mitochondria
♣ Animals cannot produce sugars from even chain length fatty acids (but can odd length)
♣ Fatty acid synthesis occurs in the cytoplasm
♣ Synthesis and degradation are tightly regulated.
