Lipids 3 Flashcards
(32 cards)
Where do we get fatty acids/
- Diet (essential fatty acids)
- Synthesis from excess carbohydrate and protein components (acetyl CoA)
Where does FA synthesis occur?
- Liver
- Lactating mammary gland
- Adipose tissue
Describe de novo synthesis of FA?
- FA synthesised from acetyl CoA, derived from excess protein, fat and carbohydrate
- Uses ATP and NADPH
- Occurs in the cytosol
- Acetyl CoA formed in the mitochondria so needs transferred to cytosol
When does the citrate shuttle occur?
When the citrate concentration in mitochondria is high
What enzymes are involved in FA synthesis?
- Acetyl CoA carboxylase (activation/regulation)
- Fatty acid synthase (multifunctional)
What is need for FA synthesis?
Acetyl CoA and NADPH
What is the product of FA synthesis?
Palmitic acid
What is the committed step in FA synthesis?
Formation of malonyl-CoA
What is needed to convert Acetyl CoA to maloyl-CoA/
Acetyl CoA carboxylase
What metabolic and hormonal signal control the activity of acetyl CoA carboxylase?
- ACC is the key regulatory enzyme
- Activated by citrate (enough glucose to proceed)
- Deactivated by palmitoyl CoA (enough FA synthesised)
- Insulin activated glucagon, epinephrine inhibits
What occurs during elongation?
Acyl-malonyl ACP condensing enzyme forms acetoacetyl-ACP
What 3 reactions occur after elongation?
- Reduction
- Dehydration
- Reduction
What is the difference between reduction-dehydration-reduction and FA degradation?
NADPH is used
How many times is the elongation cycle repeated?
6 more times
What happens after palmityl-ACP is produced?
A thioesterase then cleaves the palmityl-CoA from the ACP
What does the acyl carrier protein covalently link to?
The intermediates in FA synthesis
Where does the 14 NADPH required for plalmitate synthesis come from?
- Pentose Phosphate pathway (6NAPH)
- Malic enzyme reaction (malate to pyruvate) (8NADPH)
Where does any further modification of palmitate or dietary FA take place?
In the mitochondria and ER by diverse enzymes
What are 3 specialised lipid classes?
- Steroid hormones
- Cholesterol
- Eicosanoids
What are steroid hormones?
Chemical substances that serve as chemical messengers in the body
What is cholesterol?
The starting material fro the synthesis of steroid hormones
What is eicosanoids?
They are derived from 20 carbon unsaturated fatty acids and are synthesised throughout the body
What are the functions of cholesterol?
- Component of cell membranes
- Precursor to other substances (sterol hormones, vitamin D, bile acids)
Where is cholesterol made?
Mainly in the liver
