Lipid metabolism and pathways Flashcards
List the biological functions of lipids
Essential components of cell membranes e.g. phospholipids, glycolipids, cholesterol
Energy generation and storage i.e. triglycerides
Inter- and Intra-cellular signalling events e.g. precursor of steroid hormones
Metabolism e.g. bile acids
What are metabolites?
The reactants, intermediates and products of a Series of connected enzymatic reactions that produce specific products
Describe the 2 major steps in the digestion of dietary TGs
TGs need to be first EMULSIFIED by BILE ACIDS; (bile acids are detergent-like molecules)
TGs are then HYDROLYSED by the enzyme PANCREATIC TRIACYLGLYCEROL LIPASE
What are the products of fat digestion?
Mixture of fatty acids and mono-and diacylglycerols
What are the 2 major metabolism pathways of lipids?
Oxidation in the mitochondria to release energy in the form of ATP
Synthesis of TG from acetyl-CoA (for storage)
Describe the process of oxidation of triglycerides
Oxidation of long chain fatty acids to 2-carbon fragments in the form of acetyl-CoA: THIS IS β-OXIDATION
Oxidation of acetyl-CoA to CO2 in the citric acid cycle
Transfer of electrons from reduced electron carriers to mitochondrial respiratory chain
What is beta oxidation?
Successive removal of 2-carbon fragments from fatty acids
Where does beta oxidation occur?
Occurs in mitochondria, also in peroxisomes
Describe the process of beta oxidation
1st step: fatty acids activated by attachment to Coenzyme A (CYTOSOL)
2nd step: transfer of acyl-CoA across mitochondrial membrane (RATE-LIMITING STEP)
3rd step: progressive oxidation of fatty acids by removal of 2-carbon units to form acetyl-CoA which enters the citric acid cycle
What is formed after each cycle of beta oxidation?
Each cycle: Shorten by 2C 1 acetyl-CoA formed 1 FADH2 formed 1 NADH formed
Where does fatty acid synthesis occur?
In the liver and adipocytes
Occurs in the cytosol of the cells
What occurs during fatty acid synthesis?
Long chain carbon molecules built up from 2-carbon units derived from acetyl CoA
Where is acetyl CoA found?
In the mitochondria
How does the acetyl CoA get out of the mitochondria and into the cytosol?
Via Citrate malate cycle
Acetyl CoA is converted to citrate which can be then converted back to Acetyl CoA in the cytosol
Describe the rate limiting steps
Rate-limiting steps:
β-oxidation: transfer of acyl-CoA into mitochondria
Fatty acid synthesis: formation of malonyl CoA from acetyl-CoA, catalysed by acetyl CoA carboxylase
Describe fatty acid synthesis
Malonyl CoA and acetyl CoA both bind to fatty acid synthase
A series of condensation reactions involving malonyl CoA adds further C2 units
