What happens to excess amino acids in the liver?
In the liver, excess amino acids undergo various metabolic processes. Here's what typically happens:
1. Deamination: Excess amino acids are deaminated, meaning the amino group is removed from the molecule. This process is catalyzed by enzymes called aminotransferases or transaminases. The amino group is usually transferred to a ketoacid, resulting in the formation of a new amino acid and a ketoacid.
2. Transamination: The ketoacids produced during deamination can undergo transamination reactions with other amino acids. This process allows for the transfer of amino groups between different amino acids, leading to the synthesis of various essential and non-essential amino acids as needed by the body.
3. Urea Synthesis: Amino groups that are removed during deamination are not directly excreted. Instead, they are converted into urea, the primary nitrogenous waste product in humans. Urea synthesis occurs in the liver through a series of reactions known as the urea cycle or ornithine cycle.
4. Gluconeogenesis: Some excess amino acids can be converted into glucose through a process called gluconeogenesis. During gluconeogenesis, the carbon skeletons of amino acids are converted into intermediates that can enter the glycolytic pathway, leading to the synthesis of glucose. This process helps maintain blood glucose levels during periods of fasting or when carbohydrate intake is low.
5. Ketogenesis: In certain conditions, such as prolonged fasting or a high-fat, low-carbohydrate diet, excess amino acids can be broken down to produce ketone bodies. Ketone bodies, including acetoacetate and beta-hydroxybutyrate, can serve as an alternative fuel source for the brain and other tissues when glucose is limited.
6. Protein synthesis: Excess amino acids can also serve as building blocks for protein synthesis. They are incorporated into proteins through the process of translation, where the genetic information in messenger RNA (mRNA) is converted into a sequence of amino acids, forming new proteins essential for various cellular functions.
7. Catabolism and Energy Production: In some cases, excess amino acids that cannot be utilized for protein synthesis or other metabolic purposes may undergo catabolism and be converted into energy. The carbon skeletons of amino acids can be broken down through the citric acid cycle (Krebs cycle), generating energy in the form of adenosine triphosphate (ATP).
It's worth noting that the liver plays a central role in amino acid metabolism, regulating the levels of various amino acids in the body and converting excess amino acids into other essential compounds through these different metabolic pathways.