Protein Catabolism
"Catabolism is the biological process through by which large molecules are broken into smaller molecules. Energy is released during this reaction."
Catabolism reaction in our body.
- Polysaccharides like cellulose and starch are complex molecules of glucose monomer unit. They are broken down to glucose units.
- Nucleic acids like DNA and RNA are made up of bases like purines and pyrimidines along with pentose sugar. They are broken down to their constituent bases and sugars which can be used as energy source.
- Proteins are complex polymer of many α-amino acids. They are broken down to simple amino acids which can in turn be again recycled to get another protein or even they may be decomposed to give glucose which is energy source.
- Glucagon is a hormone produced in our body. It interacts with glycogen stored in the pancreas of our body to break it to simple glucose. Glucose molecules are stored as glycogen in our body and they are broken when required by glucagon.
Amino acid are catabolize in liver from the source of :
- Diet
- Biosynthetic reaction
- Normal turnover of intracellular protein
The removal of nitrogen in amino acid
Removal of 2 Nitrogen from an amino acid involve 2 stage :
- Deamidation -- Remove one nitrogen from R-group of an amino acid
- Transamination -- removal of the amino group in an amino acid
What is Oxidative Deamidation?
Oxidative deamination is a form of deamination that generates oxoacids in the liver.
The presence of nitrous acid can cause transition mutations, by converting cytosine to uracil. Oxidative deamination occurs primarily in the liver and kidneys.
The presence of nitrous acid can cause transition mutations, by converting cytosine to uracil. Oxidative deamination occurs primarily in the liver and kidneys.
Urea Synthesis
- Urea is the major end product in Nitrogen metabolism in human and mammals. NH3, the product of oxidative deamidation reaction, is toxic in even small amount and must be removed from the body. Urea cyvle a.k.a Orthine cycle is the conversion reactions of NH3 into urea.
- The reaction occur in liver (certain occur in cytosol and mitochondria). The urea is transported to the kidney where it excreted.
- One amine group is come from oxidative deamidation of glutamic acid - while the other group come from aspartic acid
- The fumaric acid first undergoes reactions through a portion of citric acid cycle (krebs cycle) to produce oxaloacetate acid which is then changed by transamination into aspartic acid.
Disorder of amino acid catabolism :
- Alkaptoneuria is a result of deficiency in homogentisate oxidase. The substrate is excreted in the urine and turns black on oxidation.
- Albinism result from a lack of thyrosinase and thus melanin is not produced. Albinos get skin cancer easily.