When talking about a person’s appearance, special abilities, or behaviour, people say ‘it’s in your genes’. Factually, the genetic information in the DNA sequence plays a crucial role in determining one’s physical traits, such as hair colour, eye shape, blood group, and even the likelihood of being affected by certain illnesses.
Have you ever wondered how specific nucleotide sequences called A, C, G, and T lead to salient physical properties? The central dogma answers precisely that by providing a basic framework for how genetic information flows from DNA sequences to intracellular protein products; the process is called gene expression.
What is the central dogma of molecular biology, and what processes are involved?
The central dogma of molecular biology in a biological system explains the flow of genetic information. It means that the ‘DNA produces RNA and RNA produces protein’, though this is not the original meaning and was first noticed in 1957 by Francis Crick.
In simple terms, the central dogma means that once ‘information’ enters a protein, it cannot escape. More specifically, it may be possible to transfer information from the nucleic acid to the nucleic acid, or from the nucleic acid to a protein, but not from a protein to a protein, or from a protein to the nucleic acid. The information defines an accurate sequence determination from either the nucleic acid or amino acid residue in the protein.
Processes involved in the central dogma
There are two steps in the process of the central dogma.
- Replication
- Transcription
- Translation
What is DNA replication?
DNA replication is probably one of the most amazing tricks of DNA. Each cell has the required DNA to make other cells, and this way, a single cell can give rise to trillions of cells.
In cell division, all information needs to be replicated entirely. In other words, DNA is a molecule that can replicate and make an almost perfect copy of itself. Replication uses a DNA polymerase, a molecule specially designed to copy DNA.
When the entire DNA is wholly replicated, the cell contains twice as much DNA as it needs and then spits that DNA and packages it into daughter cells. In some cases, the cells are entirely identical.
Transcription
- This is the first step in gene expression, copying a segment of the DNA into the RNA. DNA sequence information is converted to RNA by a process called transcription.
- The transfer of information from a DNA strand to the RNA occurs by RNA polymerase enzymes.
- This DNA strand where transcription occurs consists of three parts: promotor, structural gene, and the terminator.
- The DNA strand that synthesises RNA is the template strand, the DNA strand that codes for RNA are the coding strand.
- DNA-dependent RNA polymerase bound to the promoter at the 3′-5’direction and catalysed polymerisation.
- As it approaches the terminator, the newly synthesised RNA strand is released. These released strands are modified post-transcriptionally.
Translation
- Proteins are encoded by RNA through a process called translation. Translation Is an active process that requires energy provided by the charged tRNA molecule.
- Ribosomes, composed of larger and smaller subunits, initiate the translation process.
- The larger subunit is composed of two tRNA molecules placed adjacent to each other so that they can consume enough energy to form a peptide bond. The mRNA enters the small subunit, is present in the large subunit, and is retained by codon-complementary tRNA molecules.
- Two codons are held together by two tRNA molecules placed close to each other, forming a peptide bond. A long polypeptide chain of amino acids is formed during the process.
Genetic code
The genetic code contains information about proteins made from RNA. There are essentially three nucleotides and four nitrogen bases, forming the triplet codon that encodes the amino acid. Therefore, the number of possible amino acids is 4 x 4 x 4 = 64 amino acids.
There are 20 kinds of natural amino acids. Of the 64 codons, three stop codons stop the transcription process, and one is the start codon. H.
Some amino acids are encoded by multiple codons and, therefore, degenerate. Each codon encodes only one particular amino acid, and the code is universal regardless of the species of the organism.
Conclusion
The facts of central dogma are not only restricted to humans but are universal to all living beings. The central dogma of molecular biology shows that the DNA encodes the RNA, and the RNA encodes proteins, helping us learn about the messenger RNA, transfer RNA, ribosomal RNA, and the roles it plays in the protein assembly process.