The “genetic code” is what determines the late protein’s amino acid sequence.<\/div><\/p>\n\n\n\n Central dogma is a principle where we are talking about the transition of the information from the DNA to the RNA, and from the RNA to the translated protein.<\/p>\n\n\n\n The dogma itself includes two major processes (Figure 1):<\/p>\n\n\n\n The transcription and the translation altogether called “protein synthesis” also which is different in the prokaryotes and the eukaryotes.<\/p>\n\n\n\n The genetic code of an amino acid consist of three nucleotides. The genetic code library consists of 64 triplet codons (A, G, C, U<\/strong>) 43<\/sup>= 64. In eukaryotes multiple codons are there for a single amino acid. To produce the 20 amino acid in eukaryotes, we need a flexible system, which is supported by the multiple chances and variability by the codons.<\/p>\n\n\n\n Codon sequence is recognized by the anticodons, which can be found on the transfer RNA (tRNA). The recognition process called “translation” and happens in the cytosol by the help of transfer RNAs. Every amino acid has its own tRNA. <\/p>\n\n\n\n Every protein synthesis -translation process starts with a START codon, which is the amino acid METHIONINE (MET<\/strong>) every time and we have 3 optional STOP codons (Figure 2<\/strong>).<\/p>\n\n\n\n Transcription means the copy of the genetic information from the DNA into the messenger RNA (mRNA) in the nucleus. With this process we can copy all of the information which is coding amino acids (codons) but also those ones which are not coding any of them.<\/p>\n\n\n\n The transcription detailed progress is going to be discussed later in a separate topic, however the basic molecular mechanisms are compulsory to know. <\/p>\n\n\n\n To understand the biochemical\/molecular mechanism let’s take an example:<\/p>\n\n\n\n Your body is a miracle to keep so many enzymes but also has some limitations. We don’t have all the enzymes of ours every time. It is more beneficial if we open the DNA and copy the information and synthesize some of them if we need them. For example, after lunch when you eat a slice of meat. For that, you will need some enzymes.<\/em><\/p>\n\n\n\n You will open the DNA and use of RNA polymerase II<\/strong> enzyme and basic transcription factors<\/strong> (TF) to initiate the transcription. The basic transcription factors in eukaryotes are the TFII -A, B, D, E, F, H (Figure 3<\/strong>).<\/p>\n\n\n\n In the transcription all the information are copied into the mRNA, however in that case we will have the non-coding sequences too. We need to clean that mRNA up, which called the “maturation” of the mRNA. This phenomenon happens only in eukaryotes. In the prokaryotes, there is no need for mRNA processing\/maturation. <\/p>\n\n\n\n The primary transcript called “pre-mRNA”, which contains the coding so-called EXON regions and the non-coding, INTRON regions. The pre-mRNA maturation involves (Figure 4<\/strong>):<\/p>\n\n\n\n The 7-methylguanosine residue cap<\/strong> is attached to the 5′-terminal end of the primary transcripts where a poly-adenosine tail <\/strong>of about 200 adenylate residues is added at the 3\u2019 end. The RNA splicing <\/strong>removes the non-coding introns, followed by the mature mRNA transport the nucleus.<\/p>\n\n\n<\/span>\n The translation works with the mature mRNA in the cytosol where the ribosomes are attaching to the newly synthesised mRNA. In the case of the ribosomes we have differences (Figure 5):<\/p>\n\n\n\n The “S” stands for the sedimentation value (centrifugation for the separation) it shows how fast it is going down in a fractionation method.<\/em><\/p>\n\n\n\n To induce the translation we need to capture all the amino acids with their tRNAs. To bind the amino acid together with the tRNA we need to activate them by the presence of ATP. The amino acids every time are connected to the 3′ end of the tRNA. <\/p>\n\n\n\n The tRNA structure has 3 loops from which the middle one is the most important, that is responsible for the sequence complementation. That binding we call codon-anticodon connection (Figure 6). <\/p>\n\n\n\n To activate the amino acid we require ATP molecules. The activation goes in a way that the phosphate groups in the ATP are going to replaced by the aminoacid generating the Adenylated amino acid. That stage we call “activated amino acid”. In the next step, the activated adenylated amino acid ribose and the base part removed as AMP, while the transfer RNA grabs the amino acid part (Figure 7).<\/p>\n\n\n\n The translation starts with an initiation process involving the eukaryotic initiation factors (eIF) or prokaryotic initiation factors (IF). Both cases require the AUG-MET-START CODON in the mRNA sequence.<\/p>\n\n\n\n In the case of the prokaryotes, there is a special sequence that is needed, called the Shine-Dalgarno (SD) sequence. The recognition and binding are helped by the IF1, IF3 and GTP bound IF2 & tRNA & aminoacid. The translation in the case of the prokaryotes polycistronic means from the same mRNA different proteins can be translated (Figure 8<\/strong>). <\/p>\n\n\n\n In the case of the eukaryotic system, the translation is monocistronic, only one protein is translated from an mRNA.<\/p>\n\n\n<\/span>\n The elongation and termination processes are the next two major mechanisms to make the polypeptide change longer and to terminate it with the STOP codon. <\/p>\n\n\n\n Termination happens when a stop codon in the mRNA (UAA, UAG, or UGA) enters the A site. Stop codons are recognized by proteins called release factors, which fit neatly into the P site (though they aren’t tRNAs). Release factors mess with the enzyme that normally forms peptide bonds: they make it add a water molecule to the last amino acid of the chain. This reaction separates the chain from the tRNA, and the newly made protein is released.<\/p>\n<\/span>Central dogma<\/h2>\n<\/span>\n\n\n
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<\/a>The genetic code – codon vs. anticodon<\/h2>\n<\/span>\n\n\n
<\/a>Transcription – copying the information from the DNA into the mRNA<\/h2>\n<\/span>\n\n\n
<\/a>Maturation of the pre-mRNA<\/h2>\n<\/span>\n\n\n
<\/a>Translation of the information from the mRNA into the protein amino acid sequence<\/h2>\n<\/span>\n\n\n
<\/a>Amino acid activation<\/h2>\n<\/span>\n\n\n
<\/a><\/a>Initiation<\/h2>\n<\/span>\n\n\n
<\/a>Elongation<\/h2>\n<\/span>\n\n\n
<\/a>Termination<\/h2>\n<\/span>\n\n\n