The Central Dogma of Molecular Biology

The central dogma of molecular biology describes how genetic information flows from DNA to RNA to produce a functioning output, a protein. According to the fundamental dogma, DNA contains all the necessary information to produce our proteins, and RNA is a messenger that transports this information to the ribosomes. Ribosomes behave as cells’ factories, converting information from a code into a functioning product.

The Central Dogma

• The central dogma of molecular biology describes the movement of genetic information within a biological system.
• It claims that once ‘information’ has transferred into protein, it cannot be retrieved.  
• Information transmission from nucleic acid to another nucleic acid or from nucleic acid to protein may be conceivable. Still, transfer from one protein to another or from a protein to nucleic acid is impossible.
• Here, information refers to the accurate identification of sequence, either base in a nucleic acid or amino acid residues in a protein.
• In the most frequent or broad example, dogma provides a framework for understanding the transmission of sequence information between information-carrying biopolymers in living organisms.
• There are three primary types of biopolymers: DNA, RNA (both nucleic acids), and protein.
• There are 3 X 3 = 9 possible direct information exchanges between them.
• The doctrine divides them into three groups of three: three general transfers (believed to occur routinely in most cells), two special transfers (known to occur, but only under certain conditions in the case of some viruses or a laboratory), and four unknown transfers that are believed never to occur).
• The general transfers define the typical flow of biological information: DNA may be replicated to DNA, DNA information can be translated into mRNA (transcription), and proteins can be produced utilising the information in mRNA as a template (translation).
• The particular transfers explain RNA replication and DNA synthesis utilising an RNA template (reverse transcription).

Central Dogma Steps

• All cells employ transcription and translation to preserve their genetic information and turn the genetic information stored in DNA into gene products, either RNAs or proteins, depending on the gene.
• Transcription occurs within the nucleus of eukaryotic cells, whereas translation occurs outside the nucleus in the cytoplasm.
• Both the processes occur in the cytoplasm of prokaryotic cells or cells without a nucleus.

Described below are the steps through which the central dogma is implemented:

Transcription: DNA to RNA

• The activity of the creation of a matching RNA copy of a DNA sequence is referred to as transcription. 
• Both RNA and DNA are nucleic acids that employ nucleotide base pairs as a corresponding language that enzymes can render from DNA to RNA.
• A DNA sequence is read by RNA polymerase during transcription, which results in forming a corresponding, antiparallel RNA strand. 
• Unlike DNA replication, transcription produces an RNA complement that replaces the RNA uracil (U) in all places where the DNA thymine (T) would have been present.
• The initial stage in central dogma is transcription.
•  A transcript is the segment of DNA that has been transcribed into an RNA molecule. 
• Some transcripts function as basic or regulatory RNAs, whereas others encode one or more proteins. 
• If the transcribed gene encodes a protein, the transcription output is messenger RNA (mRNA), which is subsequently utilised to produce that protein during the translation process.

Translation: RNA to Protein

• The translation is the activity of untangling and rendering mRNA to create a polypeptide sequence, also referred to as a protein. 
• The mRNA directs this form of protein synthesis, which is carried out with the assistance of a ribosome, a huge complex of ribosomal RNAs (rRNAs) and proteins. 
• A cell decodes the genetic message of the mRNA and collects the brand-new polypeptide chain during translation. 
• Transfer-RNA(tRNA) converts the codon sequence on the mRNA strand.
• The primary purpose of tRNA is to transport a free amino acid from the cytoplasm to a ribosome, where it is connected to the developing polypeptide chain. 
• tRNAs keep adding the amino acids to the stretching edge of the polypeptide chain till they arrive at a stop codon on the mRNA. 
• The ribosome then delivers the finalised protein into the cell.

The Genetic code

• The genetic code is flawed because there are 64 potential nucleotide triplets (43), significantly more than amino acids. 
• Codons are nucleotide triplets that direct the insertion of a specific amino acid into a polypeptide chain. 
• Sixty-one of the codons are responsible for encoding twenty distinct amino acids. 
• Many codons can encode the majority of these amino acids. 
• Three of the 64 codons stop protein synthesis and allow the polypeptide to release the translation machinery. 
• These triplets are referred to as stop codons. 
• The stop codon UGA is occasionally used to encode selenocysteine (Sec), a 21st amino acid, but only if the mRNA contains a particular sequence of nucleotides known as a selenocysteine insertion sequence (SECIS).
• Some microorganisms employ the stop codon UAG to encode pyrrolysine, a 22nd amino acid (Pyl). 
• The codon AUG also has a purpose. It not only specifies the amino acid methionine, but it also serves as the start codon for translation to begin. 
• The AUG start codon determines the reading frame for translation.
• All living things share the genetic code. With a few exceptions, almost all organisms employ the same genetic code for protein synthesis. 
• The universality of the genetic code is compelling evidence that all life on Earth had a common ancestor.

Conclusion

The central dogma of molecular biology explains how genetic information flows in cells from DNA to messenger RNA (mRNA) to protein. It is stated that genes determine the sequence of mRNA molecules, which determines the sequence of proteins.