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why tRNA binds to amino acid & mRNA codon during protein synthesis ?
The process of converting the genetic message found in mRNA to an amino acid sequence (protein synthesis) is called translation.The ribosome is made up of a large and small subunit, and is a large enzyme comprised mostly of ribosomal RNA (rRNA), with proteins interspersed like islands in a sea of RNA. Besides the rRNA, the ribosome contains binding sites for tRNA and mRNA. The rRNA forms most of the ribosomal structure and performs the catalytic steps of peptide synthesis, the mRNA delivers the genetic message, and tRNA translates the genetic code into peptide sequence
Protein synthesis begins when a charged tRNA, mRNA, and the small and large ribosomal subunits (30S and 50S for E. coli) come together to form the initiation c complex (70 S in E. coli). The initiation complex contains a peptidyl binding site, (P site) and an aminoacyl binding site (A site). The first tRNA to bind is always the initiator tRNA, tRNAfMET. tRNAfMET binds to the start codon of mRNA, AUG. The first amino acid of the protein is thus methionine.
 tRNAs have an anticodon loop that pairs with a mRNA codon tRNAs are narrow so as to be able to sit next to one another on adjacent mRNA codons in the P and A sites
an mRNA molecule binds to the small ribosomal subunit at the mRNA binding site.
 A special tRNA, called initiator tRNA, binds to the start codon (AUG) on mRNA, where translation begins. The tRNA anticodon (UAC) attaches to the mRNA codon (AUG) by pairing between the complementary bases. Besides being the start codon, AUG is also the codon for the amino acid methionine. Thus, methionine is always the first amino acid in a growing polypeptide
 Next, the large ribosomal subunit attaches to the small ribosomal subunit-mRNA complex, creating a functional ribosome. The initiator tRNA, with its amino acid (methionine), fits into the P site of the ribosome.


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