Zusammenfassung der Ressource
Fatty Acids
- Fatty Acid Biosynthesis
- Occurs in the cytoplasm
- Occurs in the liver, kidney, brain, lungs, mammary and adipose tissue
- Acetyl coA myst first be converted into
malonyl CoA by acetyl CoA carboxylase.
Anmerkungen:
- Acetyl CoA carboxylase is allosterically activated by citrate and isocitrate and inhibited by palmitoyl CoA negative feedback.
- Insulin stimulates acetyl CoA carboxylase activity.
Glucagon and adrenalin inhibit it by increasing intracellular levels of cAMP.
- Formation of malonyl CoA involves covalent
binding of CO2 to biotin using ATP hydrolysis.
- Using the same enzyme, CO2 is then tranferred
to acetyl CoA, producing malonyl-CoA
- Remaining reactions take place on a multifunctional protein called
fatty acid synthetase (FAS)
- Initial condensation involves an
acetyl group and a malonyl group.
- Acetyl group and malonyl group must be
transferred from their CoA derivatives to a
condensing enzyme and ACP.
Anmerkungen:
- Catalysed by acetyl transacetylase (ATP) and malonyl transacetylase (MT)
- Four reactions - condensation,
reduction, dehydration and then
another reduction.
- Lipolysis
- TAG is formed from acyl CoA and
glycerol-3-phosphate in the adipose
tissue.
- Glucose entry into the adipocytes is facilitated by GLU4 transporter
Anmerkungen:
- GLUT 4 - Translocated from the Golgi complex to the plasma membrane in the presence of insulin.
- When glucose levels are high, a large proportion is
converted to acetyl CoA and then to LCFA or goes
into the TCA cycle.
- As glucose runs out, it is directed to the
formation of glycerol 3-phosphate and
TAG.
- Insulin also activates lipoprotein lipase
(LPL) resulting in the hydrolysis of TAG
contained in the chylomicrons.
- Provides FA for esterfication with G-3-P inside adipose tissue.
- Regulation
- Adrenalin act rapidly in promoting lipolysis
by stimulating membrane bound adenyl
cyclase, thus increasing levels of cAMP
- Increasing levels of cAMP are responsible for converting inactive HSL into its active
phosphorylated form thus promoting lipolysis
Anmerkungen:
- cAMP stimulates cAMP-dependent protein kinase (PKa)
- Intracellular cAMP levels are reduced through the
activity of cAMP dependent phosphodiesterase which
is activated by insulin.
- Glucocorticoids promote lipolysis through a cAMP-independent pathway.
- They promote gene transcription and so increase HSL biosynthesis.