Introduction
The genetic code is a collection of laws that define how DNA’s four-letter code is converted into a 20-letter code, which serves as the building block of proteins. The genetic code is consist of codons, which are 3 –letters nucleotide pairings that each correspond to a distinct amino acid or stop signal. Francis Crick and his colleagues initially proposed the notion of codons in 1961.
Some properties of genetic code are- A triplet is a code, degenerate, non-overlapping, comma less, unambiguous
Genetic Code
A gene’s instructions inform a cell how to generate a certain protein. Letters in DNA code are A, C, G, and T, which stand for the chemicals adenine, cytosine, guanine and thymine respectively which make up the nucleotide bases of DNA.
The coding of each gene combines the four chemicals in different ways to form three-letter “words” that define which amino acid is required at each step of the protein-making process.
From the four nucleotides, there are 64 potential P&C, of three-letter nucleotide sequences. There are 61 amino acids and three stop signals among the 64 codons. The genetic code is degenerate since a single amino acid can be coded for by more than 1 codon, the fact that each of it is specialised for just one amino acid (or one-stop signal).
It’s also worth noting that the genetic code does not overlap, which means that each nucleotide belongs to just one codon and cannot be found in two neighbouring codons.
Characteristics of Genetic Code and Key Properties of Genetic Code
1. A triplet codon is used
The nucleotides in mRNA are organised into a linear series of codons, with each codon consisting of three nitrogenous bases in succession, i.e., it is a triplet codon. Two types of point mutations have been used to support the idea of triplet codons: frameshift mutations and base substitutions.
(i) Frameshift mutations
The genetic code is read in a particular frame in a succession of three-letter words after it is launched at a fixed position. Any deletion or addition of one or more bases would cause the framework to be disrupted.
When frameshift mutations are crossed, they create wild type normal genes in specific combinations. It was determined that one was a deletion and the other was an addition, implying that the frame’s disordered order will be restored by the other.
(ii) Base substitution
If one base pair is replaced by another in an mRNA molecule at a specific position without any deletion or addition, the meaning of one codon containing that altered base will be modified. As a result, another amino acid will be substituted for a specific amino acid at a specific location in a polypeptide.
2. Degeneracy
The coding is degenerate, which implies that more than one base triplet codes for the same amino acid. Degeneracy in protein synthesis does not indicate a lack of specificity.
It simply implies that more than one base triplet can drive an amino acid to its proper location in the peptide chain. The three amino acids arginine, alanine, and leucine, for example, contain six synonymous codons apiece.
There are two forms of coding degeneracy: partial and total.
The first two nucleotides of a partly degenerate codon are similar, but the third (i.e., 3′ base) nucleotide varies; for example, CUU and CUC code for leucine.
When any of the four bases can take the third position and yet code for the same amino acid, complete degeneracy occurs; for example, UCU, UCC, UCA, and UCG all code for serine.
3. Doesn’t overlap
The genetic code doesn’t overlap, which means that neighbouring codons don’t overlap.
The term “nonoverlapping code” refers to the employment of the same letter for two separate codons. To put it another way, no one base can be involved in the production of several codons.
4.No commas
In the genetic code (or comma-free). There is no signal to indicate when one codon ends and the next begins.
Between the codons, there are no intervening nucleotides (or commas).
5. Non-ambiguity
A non-ambiguous code is one in which a certain codon is not ambiguous.
6. There is polarity in the code
the code is always read in the same direction, i.e. in the 5’3′ direction. To put it another way, the codon possesses polarity. Because the codon’s base sequence is inverted, it is obvious that if the code is read backwards, it will define two distinct proteins.
7. The code is universal
the same genetic code has been discovered to be valid in all creatures, from bacteria to humans. Marshall, Caskey, and Nirenberg (1967) discovered that E. coli (Bacterium), Xenopus laevis (Amphibian), and guinea pig (mammal) amino acyl-tRNA utilise almost the same coding.
8. Some codons operate as stop codons
The chain stop or termination codons are UAG, UAA, and UGA. They can’t code for any of the amino acids. These codons aren’t read by any tRNA molecules (due to their anticodons), but they are read by a group of proteins known as release factors (e.g., RF-1, RF-2, RF-3 in prokaryotes and RF in eukaryotes).
9. Some codes operate as start codons
The AUG codon is the start or initiation codon in most organisms, meaning that the polypeptide chain begins with methionine (eukaryotes) or N- formylmethionine (prokaryotes) (prokaryotes). The starting site of mRNA which has the AUG is bound to N-formylmethionyl-tRNA.
Conclusion
We have learned the types of genetic codes, their characteristics, and key properties, also given that the code explains how information is transmitted from DNA to mRNA to protein at a molecular level (the central dogma of biology). The dynamics and circumstances that influence how the nucleotide triplet code translates into amino acid sequences are fundamental to genetics and molecular biology.
Lastly, the information in DNA as a nucleotide sequence is important for the production of proteins, which are required for cell and organism function.