Genetic code microbiology molecular biology

Genetic code properties of genetic code

1. Genetic code and its Characteristics Presented by: Mrs. Anjula Chaudhary Assistant Professor School of Biosciences IMS Ghaziabad UC campus

2. Flow of Genetic I nformation

3. Genetic Code The genetic code may be defined as the exact sequence of DNA nucleotides read as three letter words or codons , that determines the sequence of amino acids in protein synthesis . or The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal. 

4. Genetic code… There are 64 possible combinations , of three-letter nucleotide sequences that can be made from the four nucleotides.  With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins. The codons are of two types : (1) Sense codons ( 2 ) Signal codons.  

5. Genetic code Sense Codon: Those codons that code for amino acids are called sense codons. There are 61 sense codons in the genetic code which code for 20 amino acids . Signal Codons: Those codons that code for signals during protein synthesis are known as signal codons. There are four codons which code for signal. These are AUG, UAA, UAG and UGA .

6. Genetic code History The concept of codons was first described by Francis Crick and his colleagues in 1961.  Marshall Nirenberg and Heinrich Matthaei performed experiments for deciphering the genetic code in 1961. Later on, Nirenberg , Philip Leder , and Gobind Khorana identified the rest of the genetic code and fully described each three-letter codon and its corresponding amino acid.

7. Picture source: biology world

8. Properties of genetic code Some important properties genetic code are. The genetic code is: (i) Triplet (ii) Universal (iii) Comma-less (iv) Non-overlapping (v) Non-ambiguous (vi) Redundant (vii) Has polarity

9. Genetic code table Image credit: " The genetic code ," by OpenStax College, Biology 

10. Triplet The genetic code is triplet. The triplet code has 64 codons which are sufficient to code for 20 amino acids and also for start and stop signals in the synthesis of polypeptide chain . Example ..UUU

11. Universal The universality of genetic code was explained by Marshall, Caskey and Nirenberg (1967) who found that E. coli (Bacterium), Xenopus laevis (Amphibian) and guinea pig (mammal) amino acyl- tRNA use almost the same code. 

12. Deviation from universality picture source: Plant Cell Biology For Masters

13. Comma less Genetic code is comma less means that no punctuation or comma is used between the codons. It is continuous no letter is used in between.

14. Non overlapping Non overlapping codes means that the base in m-RNA is not used for two different codes. it has been shown that in the bacteriophage ɸ × l74 there is a possibility of overlapping the genes and codons (Barrel and coworkers, 1976; Sanger, et al., 1977).

15. Unambiguous and Degenerate Unambiguous nature of the code means that same codon will code for only one amino acid where ever it is present. Degenerate nature of genetic code means that there is more than one codon for same amino acid but it will always code for the same amino acid.