Cuerpos cetónicos [cetoGÉNESIS y cetóLISIS]

Cetogenesis and Ketone Bodies

The discussion delves into the biochemical pathway of ketogenesis, focusing on the formation of ketone bodies as an alternative fuel source when glucose levels are low. Various conditions that can trigger ketogenesis are explored.

Formation of Ketone Bodies

• Ketogenesis occurs in conditions such as low glycogen reserves, low blood glucose levels, ketogenic diet (low carb, high fat), untreated type 1 diabetes leading to prolonged ketosis.

• Factors triggering ketogenesis include prolonged fasting, high energy demand during extended exercise, chronic alcohol consumption.

Biochemical Process of Ketogenesis

• Ketogenesis takes place in the mitochondria of hepatocytes, specifically in the mitochondrial matrix.

• Activation of free fatty acids by acyl-CoA synthetase allows their entry into the mitochondria via carnitine palmitoyltransferase 1 (CPT1).

Steps in Ketone Body Formation

• Initial step involves condensation of two acetyl-CoA molecules to form acetoacetyl-CoA catalyzed by thiolase enzyme.

• Acetoacetyl-CoA combines with another acetyl-CoA to produce β-hydroxy β-methylglutaryl-CoA (HMG-CoA), involving HMG-CoA synthase enzyme.

Production and Utilization of Ketone Bodies

• HMG-CoA is converted to acetoacetate by HMG-CoA lyase enzyme, forming the first ketone body. Acetoacetate can be used as fuel or converted to β-hydroxybutyrate in the liver.

• Beta-hydroxybutyrate is a major circulating ketone body utilized for energy production in extrahepatic tissues like heart, kidneys, skeletal muscle, and brain.

Utilization of Ketone Bodies

Explores how extrahepatic tissues utilize ketone bodies for energy production through a process called ketolysis.

Process of Ketolysis

• Extrahepatic tissues undergo ketolysis where beta-hydroxybutyrate is converted to acetoacetate by beta-hydroxybutyrate dehydrogenase enzyme in the mitochondrial matrix.

• This conversion requires NAD+ to NADH reduction due to low energy state in these tissues. Acetoacetate can come from liver-produced acetoacetate or beta-hydroxybutyrate directly.

Detailed Biochemical Process Explanation

In this section, the speaker delves into the biochemical process involving the breakdown of acetacilcoenzyme A and its conversion to energy in extrahepatic tissues through ketone bodies.

Breakdown of Acetacilcoenzyme A

• The liver does not contain the enzyme thioforase, crucial for ketone body utilization, leading to the liver not consuming ketone bodies.

• Coenzyme A is incorporated into the process from the Krebs cycle, focusing on utilizing acetilcoa's acetate group.

Energy Production and Ketone Body Conversion

• The Krebs cycle generates NADH, FADH, and GTP which are utilized in oxidative phosphorylation for ATP production in extrahepatic tissues.