<P> The first product of transcription differs in prokaryotic cells from that of eukaryotic cells, as in prokaryotic cells the product is mRNA, which needs no post-transcriptional modification, whereas, in eukaryotic cells, the first product is called primary transcript, that needs post-transcriptional modification (capping with 7 - methyl - guanosine, tailing with a poly A tail) to give hnRNA (heterogeneous nuclear RNA). hnRNA then undergoes splicing of introns (noncoding parts of the gene) via spliceosomes to produce the final mRNA . </P> <P> Phenomena of amino acid assembly from RNA . The synthesis of proteins from RNA is known as translation . In eukaryotes, translation occurs in the cytoplasm, where the ribosomes are located . Ribosomes are made of a small and large subunit that surround the mRNA . In translation, messenger RNA (mRNA) is decoded to produce a specific polypeptide according to the rules specified by the trinucleotide genetic code . This uses an mRNA sequence as a template to guide the synthesis of a chain of amino acids that form a protein . Translation proceeds in four phases: activation, initiation, elongation, no and termination (all describing the growth of the amino acid chain, or polypeptide that is the product of translation). </P> <P> In activation, the correct amino acid (AA) is joined to the correct transfer RNA (tRNA). While this is not, in the technical sense, a step in translation, it is required for translation to proceed . The AA is joined by its carboxyl group to the 3' OH of the tRNA by an ester bond . When the tRNA has an amino acid linked to it, it is termed "charged". Initiation involves the small subunit of the ribosome binding to 5' end of mRNA with the help of initiation factors (IF), other proteins that assist the process . Elongation occurs when the next aminoacyl - tRNA (charged tRNA) in line binds to the ribosome along with GTP and an elongation factor . Termination of the polypeptide happens when the A site of the ribosome faces a stop codon (UAA, UAG, or UGA). When this happens, no tRNA can recognize it, but releasing factor can recognize nonsense codons and causes the release of the polypeptide chain . The capacity of disabling or inhibiting translation in protein biosynthesis is used by some antibiotics such as anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, puromycin, etc . </P> <P> Events that occur during or following biosynthesis include proteolysis, post-translational modification and protein folding . Proteolysis may remove N - terminal, C - terminal or internal amino - acid residues or peptides from the polypeptide . The termini and side - chains of the polypeptide may be subjected to post-translational modification . These modifications may be required for correct cellular localisation or the natural function of the protein . During and after synthesis, polypeptide chains often fold to assume, so called, native secondary and tertiary structures . This is known as protein folding and is typically required for the natural function of the protein . </P>

Which of the following is a step in translation