In eukaryotes, the small subunit of the ribosome typically just “scans” along from the 5′ end of the mRNA until it finds the first AUG codon. In most cases, translation begins at the AUG triplet closest to the 5′ end of the mRNA. Translation begins near the 5′ end of the mRNA, with the ribosomal small subunit and a special initiator tRNA carrying the amino acid methionine. The amino acid attachment site (yellow) is the location where the tRNA is covalently bonded to its amino acid. The anticodon loop (in gray) base-pairs with the codon in the mRNA in anti-parallel orientation. Tertiary structure of tRNA, from Wikipedia. Cells have a family of enzymes, called amino-acyl tRNA synthetases, that recognize the various tRNAs and “charge” them by attaching the correct amino acid. The 3′ end of the tRNA has a high-energy bond to the appropriate amino acid. The bases in the anticodon loop are complementary to the bases in an mRNA codon. tRNAs match the amino acid to the codon in the mRNA. transfer RNAs (tRNAs) that are “charged” with their corresponding amino acids (meaning the tRNAs are attached to/carrying their corresponding amino acids).Thus the ribosome is actually an immense ribozyme, or a catalytic RNA molecule stabilized by numerous proteins, rather than an enzyme. When the structures of prokaryotic ribosomes were determined at high resolution, researchers were astonished to discover that the catalytic site for the peptidyl-transfer reaction (attaching new amino acids to the growing polypeptide chain) consists entirely of rRNA. When they are not working, they fall apart into the small subunit and large subunit, each consisting of a rRNA and numerous proteins. Ribosomes: Ribosomes are large assemblies of ribosomal RNA molecules (rRNAs) and dozens of proteins.(There are other types of genes which do not encode proteins, such as genes encoding rRNAs and tRNAs.) messenger RNA (mRNA): mRNAs are transcribed from protein-coding genes.Translating a sequence of bases in the RNA to a sequence of amino acids in proteins requires 3 major components: Translation is the process of using an mRNA molecule as a template to make a protein: See a more advanced molecular animation of transcription, with narration, here: Translation: RNA to Protein Notice that the narrator makes a mistake at 3:45 (that he later catches and corrects!) this mistake serves as a really important reminder of one of the major differences between DNA and RNA, so watch for it. This video gives a simplified overview of transcription.
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