Flashcards in Lipid 3 Deck (33):
Precursor for fatty acid synthesis?
How is acetyl CoA
Through fatty acid degradation
Steps to synthesise fatty acids?
1. Acetyl CoA to acetyl CoA cytoplasm
2. Link two carbons together
3. Palmitate to other fatty acids (C16 and C18 are most common)
What happens in the cytosol?
Formation of acyl-CoA
Where does synthesis and degradation take place?
Synthesis = cytosol
Degradation= mitochondrial matrix
Discuss intermediates in FA synthesis vs FA degradation?
Synthesis= intermediate covalently linked to sulfhydryl groups of an acyl carrier protein (ACP)
Degradation= intermediates covalently linked to sulphydryl group of coenzyme A
Enzyme comparison between FA synthesis and degradation?
Enzymes of FA synthesis in higher organisms are joined in a single system called fatty acid synthesis. Degradative enzymes are not associated
What's the activated donor of two carbons to the elongated growing fatty acid chain?
Malonyl ACP (driven by CO2 release)
What's the reductant in synthesis vs oxidants in degradation?
Oxidants= NAD and FAD
When does elongation of fatty acid synthesis stop?
At the formation of palmitate (C16)
What aid the further elongation and insertion of double bonds carried out by?
Other enzyme systems
What is the committed/irreversible step in fatty acid synthesis?
Formation of malonyl CoA
What does fatty acid synthesis start with?
Carboxylation of acetyl CoA to malonyl CoA
What is the formation of malonyl catalysed by?
Cytoplasmic enzyme acetyl CoA carboxylase 1
What have essential roles in regulating fatty acid synthesis and degradation of fatty acid metabolism?
Acetyl CoA carboxylase 1, acetyl CoA carboxylase 2, an isoenzyme of acetyl CoA carboxylase 1
What does synthesis of a long fatty acid chain involve?
Condensation, reduction dehydration, reduction reactions catalysed by fatty acid synthase
What determines fatty acid chain length?
What is ACP?
What intermediates in synthesis are attached to, 77 amino acid chain regarded as macro CoA
What synthesises fatty acids in animals?
Multifunctional enzyme complex
How does fatty acid synthesis in animals differ to e.coli and plants?
Linked by one large polypeptide chain in animals
What does the synthesis of palmitate require?
8 molecules of acetyl CoA
14 molecules of NADPH
What carries acetyl groups from the mitochondria to the cytoplasm?
Are mitochondria readily permeable to acetyl CoA?
No (hence citrate)
Sources for NADPH?
Transference of acetyl CoA from mitochondria to cytosol (8 formed)
Pentose phosphate pathway
Major produce of fatty acid synthase?
Where do most elongation reactions occur in eukaryotes
On the cytosolic face of the endoplasmic reticulum
What do the endoplasmic reticulum systems also do?
Introduce double bonds into long chain acyl CoA
What controls fatty acid metabolism?
Acetyl CoA carboxylase
Two allosteric controls by ACC of fatty acid synthesis?
1 stimulation of ACC by citrate (abundant acetyl CoA and ATP increases synthesis)
2 inhibition of ACC by palmitoyl coa (excess fatty acid so decreased fatty acid synthesis)
What hormone stimulates fatty acid synthesis?
Insulin (removes phosphate- activates carboxylase)
What hormones inhibit fatty acid synthesis?
Glucagon and epinephrine
What does cancer have a high demand for?
Phospholipids and fatty acid