 Now, messenger RNA is free to go inside the cytoplasm or is ready for translation. The process of translation is different in prokaryotes and the eukaryotes. In prokaryotes as we know that they do not have a true nucleus. They have a nucleotide region though but true nucleus is not present. So what happened that whenever their messenger RNA and actually their nucleotide region and their chromosome is almost continuous with the cytoplasm. So as their messenger RNA comes out of the transcription bubble, it starts translating itself. The ribosomes come and attach to it and they start translating. But in eukaryotic chromosomes, this is a more complex process because they have a nucleus and the messenger RNA has to travel through the nucleus, move out through the nuclear pores into the cytoplasm where ribosomes are present and then they have to be translated. So the messenger RNA in eukaryotes is modified because it have to move along path. It is exposed to various enzymes present inside the nucleus and cytoplasm which are called nucleases and proteases. To protect it from the enzyme action, two modifications occur in the messenger RNA. One is called a cap, addition of a cap which is a 7-methyl-GTP cap. On its 5 end, there is a 7-methyl-GTP molecule which is attached and on its other end, a poly-A tail that is A-A-A-A, adenine, adenine, adenine, adenine nucleotides are added. These are the two major additions which protect this molecule from the action of nucleases and the proteases. There is another difference between the prokaryotic and eukaryotic DNA. The eukaryotic DNA have some extra sequences inside their integrated in their genes. We call them introns. These introns have to be removed. If we look at a diagram, in the diagram in front of you, you can see that there are in green sequences of DNA called exon. Then comes an intron, then comes an exon and then comes an intron. These exons are actually the parts of genes. These introns are non-coding sequences. These does not have to code. So, what happened that before messenger RNA is translated into the proteins, these introns has to be removed. So, there is another difference between the prokaryotic and eukaryotic translation that before translation messenger RNA is we can say spliced. We call it RNA splicing, breaking down and removal of these introns from the messenger RNA molecule. If down there we have look, this is a coded gene, in which this is a coded messenger RNA molecule in which the introns are removed by different types of molecular processes, events. Next is translation. Translation is from messenger RNA to protein. messenger RNA have to code itself in the form of protein. The translation process consist of three steps. If we divide it over the length of time, we can call them three stages or three steps initiation, elongation and termination. Initiation is the start of translation. When messenger RNA in eukaryotes comes out of the nucleus through the nuclear pores and enters into the cytoplasm, it encounters the ribosomes. We know that ribosomes are the protein making machinery of the cells. But what happen in prokaryotes that when their messenger RNA starts forming coming out of transcription bubbles, it directly comes out into the cytoplasm and ribosomes come and attach to it and start translating. So, in eukaryotes introns are removed and it comes out of the nucleus, reach the cytoplasm and then it is ready to be translated. What happen actually, when messenger RNA in eukaryotes reaches in the cytoplasm, the ribosome which have two subunits, one is small and one is large, the small subunit comes and attaches to a specific site on the messenger RNA. We call it a start codon from where the actual gene starts. When the first codon is set on the small subunit is set on the first codon, then the large ribosomal unit comes and attaches to the smaller unit and the messenger RNA molecule. This larger subunit as you can see in the diagram has three sites, e-site, the exit site, p-site, the peptidal site and a-site, the amino-syle site. e-site from where a transfer RNA have to exit, the p-site where the peptide, where the transfer RNA with the peptide, the whole protein chain which is elongating is present and the a-site where the newer transfer RNA comes bringing a nucleotide. Then the first transfer RNA comes and attaches to the start codon. The first transfer RNA is an RNA molecule which have an anti codon present on itself. For example, if the start codon is AUG, then on the transfer RNA there will be a complementary sequence that due to this complementary sequence transfer RNA bringing the amino acid because according to the codon, anti codon present on the transfer RNA it will bring a specific amino acid from the surrounding cytoplasm. Transfer RNA comes and attach to the p-site. After that next transfer RNA brings another amino acid according to the codon read by the ribosome by the transfer RNA. Next transfer RNA come and attaches to the a-site. Then a peptide bond is formed between the first amino acid and the second amino acid. When this peptide bond is formed then the ribosome moves ahead on the messenger RNA. The result is this that now the first amino acid is present on the e-site and the second amino acid is present on the p-site in place of the first amino acid and the a-site as you can see in the diagram is free. When this a-site becomes free then the next transfer RNA identifies this site and brings the amino acid according to the anti codon present on this transfer RNA and comes and attaches to the a-site. When it attaches to the a-site then again a peptide bond is formed between now the second amino acid and the third amino acid. When this bond is formed then the ribosome again moves ahead due to its movement the first amino acid the first transfer RNA which brought the first amino acid according to the AUG codon the methionine is released from the e-site or the exit site and now the second transfer RNA comes on the exit site e-site and the third transfer RNA comes on the p-site and a-site is again free. Then again according to the codon read by the transfer RNA, fourth transfer RNA comes and attaches to the site again a peptide bond is formed and this process goes ahead until a stop codon comes at the end of the messenger RNA there is a codon called the stop codon this codon does not matches to any transfer RNA in place of the transfer RNA a protein complex called releasing factor comes and attaches to that site that codon and when the releasing factor comes and attaches to the codon the polypeptide is released into the site of plasm that is broken down from the transfer RNA transfer RNA is also released and the ribosomal subunits they are separated and the messenger RNA is also released from the ribosome this is how the process of translation completes. So initiation when small ribosomal subunit comes and attaches to the messenger RNA then the transfer RNAs comes according to the codons bringing amino acids and the ribosome moves on the messenger RNA to make a polypeptide chain and the end due to releasing factor they are released. So a new protein is formed in this way this may be a structural protein or this may be a functional protein.