Carnitine Shuttle Process Quiz

Study Notes

Fatty Acid Oxidation

Carnitine shuttle: transports fatty acyl CoA into the mitochondrial matrix, where fatty acid oxidation takes place.
Fatty acyl CoA is converted to fatty acyl carnitine by carnitine palmitoyltransferase I, which is inhibited by malonyl-CoA.
Short- and medium-chain fatty acids (less than 12 carbons) enter the mitochondria without the aid of carnitine or CPT system.

β-Oxidation

Sequence of 4 reactions that result in shortening by two carbons.
Oxidation of a molecule of palmitoyl CoA to CO2 and H2O produces 8 acetyl CoA, 7 NADH, and 7 FADH2.
Activation of fatty acid requires 2 ATP, but produces only 2 ATP.
Oxidation of fatty acids with an odd number of carbons requires biotin.

Ketone Body Synthesis

Takes place in liver mitochondria from acetyl CoA.
Ketone bodies are: acetoacetate, β-hydroxybutyrate, and acetone (a non-metabolized side product).
Acetoacetate and β-hydroxybutyrate are transported in blood to peripheral tissues, where they can be reconverted to acetyl CoA and oxidized by TCA.

Characteristics of Ketone Bodies

Soluble in aqueous solution.
Produced in liver during periods when the amount of acetyl CoA present exceeds the oxidative capacity of liver.
Used by extrahepatic tissues.

Regulation of Cholesterol Synthesis

HMG CoA reductase is the rate-limiting enzyme in cholesterol synthesis.
When sterol levels are low, increased synthesis of HMG CoA reductase occurs.
Insulin favors up-regulation of HMG CoA reductase gene expression, while glucagon has the opposite effect.
Statins (e.g., atorvastatin, fluvastatin) are competitive inhibitors of HMG CoA reductase used in cholesterol therapy.

Degradation of Cholesterol

Ring structure cannot be metabolized.
Sterol nucleus is eliminated by conversion to bile acids and bile salts.
Bile acids are amphipathic, acting as emulsifying agents in the intestines, helping pancreatic digestive enzymes.

Bile Acid Synthesis

Takes place in the liver by a multistep, multiorganelle pathway.
Bile acids are synthesized from cholesterol, and their structure is important for their function.

Medium-Chain Fatty Acyl CoA Dehydrogenase (MCAD) Deficiency

Autosomal recessive disorder, the most common inborn error of FA oxidation.
Causes decrease in FA oxidation and severe hypoglycemia.
Infants are particularly affected, as milk contains primarily medium-chain fatty acids.
MCAD deficiency can cause sudden infant death syndrome and Reye syndrome.

Description

Test your knowledge on the carnitine shuttle process, which involves the transport of fatty acids into the mitochondria matrix. Learn about the role of carnitine, carnitine palmitoyltransferase I, and factors affecting the shuttle process.