How proteins in the diet are disassembled and then reassembled to form useful proteins in the body - Essay Example

These enzymes are dipeptidases, carboxypeptidase and aminopeptidase. Since the intestinal absorption of proteins is only possible in amino acid form and peptide form so they must be broken down into amino acids and peptides. These absorbed peptides are dipeptides and tripeptides. After absorption they are transported into the cells by various transporters and channels depending upon the internal environment. Up till now, all the disassembly of proteins is extracellularly done. After this, the entire breakdown is done inside the cell called intracellular protein degradation.

Inside the cell, they are taken by phagocytosis; the food vacuole is fused with lysosome. The lysosomal enzymes further degrade di and tri peptides into amino acids. Different digestive enzymes have different specificity towards their substrate. For example trypsin cleaves positively charged residue including arginine and lysine. Similarly, chymotrypsin cleaves the aromatic residues consisting of tyrosine, phenylalanine and tryptophan. Elastase breaks the bond of small non-polar residues (alanine and glycine).

If these digestive enzymes are activated without any stimulus (as protein in the diet is the stimulus for their secretion), it will lead to auto-digestion of the pancreas leading to pancreatitis, that’s why they are always secreted in an inactivated form. This inactivated form is called zymogen. Zymogen for trypsin is called as trypsinogen. It is activated by enzyme enterokinase (secreted by duodenal mucosa). Pepsin is also secreted in an inactivated form as it leads to auto-digestion of stomach.

That inactivated form is called as pepsinogen which is activated in an acidic medium. The pancreas secretes the precursors of a number of proteases, such as trypsin and chymotrypsin. The intracellular degradation of protein results in the formation of amino acids. They are also degraded by ubiquitin system. After entering in the blood, amino acids are used for several purposes. One of them is also the formation of proteins for the body. Protein is also a structural component of cells. Plasma membrane and membranes of cellular organelles is also made of proteins.

So amino acids in the blood are used for the protein formation. It is a complicated process. Any mistake or error in this can lead to many diseases as discussed in the end of this essay. The assembly of proteins is called as Protein biosynthesis. It is called as Translation which involves the assembly of proteins. Translation is only possible if mRNA is available and it is formed by the process called translation. The reassembly involves two processes transcription and translation. In transcription an mRNA is generated.

It is template of one strand of double helix DNA. Transcription involves three steps: initiation of mRNA, elongation of mRNA chain and termination of transcription. Each and every step is regulated by a large number of proteins. These are transcription factors co-factors and coactivators. Their major function is to ensure that the correct and required sequence of gene is transcribed. The process of transcription occurs in the nucleus. The double helix DNA is "unzipped" or opened by the breakdown of hydrogen bonds between the two strands by helicase.

Primer attaches to the site and is followed by an initiator. Then elongation of the chain occurs by placing nitrogenous bases. The bonding occurs between adenine and uracil and guanine and cytosine.