Carnitine required for which process in fatty acid cycle?
Ans. is 'b' i.e., Fatty acid oxidation * As fatty acid is nonpolar, it passively diffuses into a cell across cell membrane. As soon as it has reached cytoplasm, fatty acid has a propensity to passively diffuses back into circulation again for the same reason - it is non polar. Fatty acid has gotten into a cell for a purpose. We can't afford to miss fatty acid. So, Fatty acid has to be trapped in a polar form. That is done by acyl CoA synthetase (three types of this enzyme are available - for short chain, medium chain and long chain), which uses two high energy phosphates (ATP - AMP + PPi) and it converts fatty acid into polar acyl CoA.* Further fate of fatty acid which is in the acyl CoA depends upon the energy status of the cell. If the energy status of the cell is already high, the fatty acid need not be oxidised but has to be stored as triacylglycerol. If the energy status of the cell is low, fatty acid has to be oxidised - for which fatty acid has to get into mitochondria. As polar acyl CoA long chain fatty acids can not cross mitochondria. They need a carrier, Carnitine (SHORT CHAIN AND MEDIUM CHAIN FATTY ACIDS ARE NOT DEPENDENT ON CARNITINE TO CROSS MITOCHONDRIA)* So carnitine is a carrier of long chain fatty acids and is involved in fatty acid oxidation.* The enzyme involved in the conversion of long chain fatty acyl co A to Acyl carnitine is Carnitine Acyl T ransferase-I (CAT-I)1. This enzyme is placed in the outer mitochondrial membrane.* After Acyl carnitine crosses the inner mitochondrial membrane, Carnitine acyl transferase II converts acyl carnitine to acyl coA and this acyl coA is oxidised.* Other facts about carnitine:# Carnitine is Beta hydroxyl gamma trimethyl ammonium butyrate.# It is synthesised from lysine and methionine in liver and kidney.# Vitamin C is required for the synthesis of carnitine.'CAT I is the enzyme which commits fatty acid to oxidation. Because, until CATI acts, the fatty acids can either get into fatty acid oxidation or they can be stored as triacylglycerol. Hence CATI is considered as the rate limiting emzyme of fatty acid oxidation
Fatty acid synthesis
Fatty acid oxidation
Fatty acid storage
Ketone body synthesis
Lipids