Metabolic Pathways: Lipid Anabolism Flashcards
When are new fatty acids synthesised?
When body has more energy than it needs (lipogenesis)
Where does lipogenesis occur?
Liver, kidney, mammary glands
What happens when we take in excess carbohydrate?
Conversion to fatty acids and triglycerides in the liver
Free fatty acids are transported in plasma bound to albumin
Triglycerides formed in the liver are transported to adipose tissue by VLDL for storage
What kind of process is lipogenesis?
Reductive process
What is the substrate for lipogenesis?
Acetyl-CoA
Where does lipogenesis occur?
Cytoplasm of liver cell
what is the problem with acetyl-coa and lipogenesis
Inner mitochondrial membrane is impermeable to acetyl-coA
What is the role of citrate?
Transports acetyl groups into the cytoplasm
- produced in the first step in TCA cycle
What is the first stage of fatty acid synthesis?
Activation of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase
Where is acetyl-coa carboxylase expressed?
Liver and adipose tissue
What does malonyl CoA do?
Donates carbon atoms to new lipid
What is the role of fatty acid synthase
Catalyses synthesis of saturated long-chain fatty acids from malonyl-CoA, acetyl CoA and NADPH
What is the structure of fatty acid synthase?
Dimer of identical polypeptides
Single polypeptide chain with seven distinct enzyme acitivites
What is the important element of fatty acid synthase?
Contains an acyl-carrier protein (ACP)
This carries the growing fatty acid chain during synthesis
What is the first step of fatty acid synthesis?
Using acetyl-CoA and malonyl-CoA as precursors, one cycle of reactions adds two carbon atoms to the growing acyl chain
- derived from malonyl-CoA
- growing acyl chain is attached to ACP
What does the cycles of reactions require fatty acid synthase?
NADPH
What is the longest length of fatty acid that can be made?
C-16 (palmitic)
What enzyme has an essential role in regulating fatty acid synthesis and degradation?
Acetyl-CoA carboxylase
What two levels does regulation occur at?
System wide mechanisms- hormones
Allosteric mechanisms
What hormones regulate acetyl-CoA carboxylase?
Insulin- only released when plenty of energy, this stimulates acetyl-CoA carboxylase
Glucagon- signals starved state, switches fatty acid synthesis off
Epinephrerine- mobilise glycogen stores, inhibiting acetyl-CoA carboxylase
Name the allosteric modulation of acetyl-CoA carboxylase
Palmitoyl-CoA: abundant when fatty acids are in excess, therefore antagonises it
Citrate: stimulates allosterically, high when acetyl-CoA and ATP are abundant
What does the synthesis of triglycerides require?
G3P
What produces G3P?
Liver, from glycerol
Adipose tissue from glucose
When does adipose tissue produce triglycerides?
In the fed state-
Insulin stimulates adipose tissue uptake of glucose
What can liver cells do to fatty acids?
Synthesised phospholipids, cholesterol and lipoproteins
