Types of Protein synthesis 1) Biosynthesis

Synthesis Biosynthesis Main article: Protein biosynthesis A ribosome produces a protein using mRNA as template. The DNAsequence of a gene encodesthe amino acidsequence of a protein. Proteins are assembled from amino acids using information encoded in genes. Each protein has its own unique amino acid sequence that is specified by the nucleotidesequence of the gene encoding this protein. The genetic codeis a set of three-nucleotide sets called codonsand each three-nucleotide combination designates an amino acid, for example AUG ( adenine- uracil- guanine) is the code for methionine. Because DNAcontains four nucleotides, the total number of possible codons is 64; hence, there is some redundancy in the genetic code, with some amino acids specified by more than one codon. [ 6 ]Genes encoded in DNA are first transcribedinto pre- messenger RNA(mRNA) by proteins such as RNA polymerase. Most organisms then process the pre-mRNA (also known as aprimary transcript) using various forms of Post-transcriptional modificationto form the mature mRNA, which is then used as a template for protein synthesis by the ribosome. In prokaryotesthe mRNA may either be used as soon as it is produced, or be bound by a ribosome after having moved away from the nucleoid. In contrast, eukaryotesmake mRNA in the cell nucleusand then translocateit across the nuclear membraneinto the cytoplasm, where protein synthesisthen takes place. The rate of protein synthesis is higher in prokaryotes than eukaryotes and can reach up to 20 amino acids per second. [ 7 ] The process of synthesizing a protein from an mRNA template is known as translation. The mRNA is loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base pairing anticodonlocated on a transfer RNAmolecule, which carries the amino acid corresponding to the codon it recognizes. The enzyme aminoacyl tRNA synthetase"charges" the tRNA molecules with the correct amino acids. The growing polypeptide is often termed thenascent chain. Proteins are always biosynthesized from N-terminusto C-terminus. [ 6 ] The size of a synthesized protein can be measured by the number of amino acids it contains and by its total molecular mass, which is normally reported in units ofdaltons(synonymous with atomic mass units), or the derivative unit kilodalton (kDa). Yeastproteins are on average 466 amino acids long and 53 kDa in mass. [ 5 ]The largest known proteins are the titins, a component of the muscle sarcomere, with a molecular mass of almost 3,000 kDa and a total length of almost 27,000 amino acids.