Genetic Code, Discovery of Genetic code.

Definition of Genetic code, Characteristics of Genetic code, Codon, Types of Codon, Initiating and terminating Codon, Mutation, Difference between Codon and Anticodon, wobble hypothesis, Silent mutation, missense mutation, nonsense mutation, frame shift Mutation

1. Genetic
Code
Presented By:-
Roshni Saiyada

2. Discovery of Genetic Code
➢Discovered by Marshal, Nirenberg, Heinrich Mathaei,
Philip Lader and Har Govind Khorana in 1968
➢Nirenberg and Khorana get Nobel prize

3. Definition of Genetic code
➢The relationship between the sequence of amino acids in polypeptide chain and
nucleotide sequence of mRNA or DNA is called genetic code.
➢ Term given by “George Gamow”.

4. Characteristics of Genetic code
✓A genetic code is tripled
✓Genetic code is continuous or comma less
✓Genetic code is degenerate
✓Genetic code is universal code
✓The code is non overlapping
✓The code is non ambiguous
✓The code is polarity

5. Codon
❖Each codon consist of three bases that specify the amino acids
of protein
❖There are 64 codons
❖61 Codons codes for amino acids and 3 codons are
Nonsense codons UAG,UGA,UAA
❖Represented in mRNA language of Adenine (A), Guanine (G), Cytosine (C), Uracil (U)
A
U
G} Codon 1
A
C
G} Codon 2
G
A
G} Codon 3
C
U
U} Codon 4
C
G
G} Codon 5
A
G
C} Codon 6
U
A
G} Codon 7

6. Types of Codon
➢Sense Codon
➢Signal Codon
Start Codon
Stop Codon
➢Sense Codon:- The codon that code for amino acids are called Sense codon
➢Signal Codon:- Those codons that code for signal during protein synthesis are
called signal codon.
For example:- AUG,UAA,UAG & UGA
➢There are two types of signal codons.
Terminating codon
Initiating codon

7. UAA, UAG & UGA are termination codons or nonsense codons & are often referred to
as amber, ochre and opal Codons
AUG is the initiation codon. It codes for the first amino acid in all proteins.
At the starting point it codes for methionine in eukaryotes and formyl methionine in
prokaryotes
Terminating Codon
Initiating Codon

8. Anticodon
The best sequence of tRNA which pairs with codon of mRNA during
translation is called anticodon.

9. Difference between Codon and Anticodon
CODON ANTICODON
Combination of three nucleotides on
mRNA.
Combination of three nucleotides on
tRNA.
Codes for specific amino acids during
translation.
Matches with codon during translation
to bring correct amino acid.

10. Wobble Hypothesis
The mechanism by which tRNA can recognize more than one codon for a specific
amino acid.
Codon-anticodon pairing follows traditional Watson crick rules for the first two
bases of codon but can be less precise for the third base in codon.

11. Wobble Hypothesis

12. Mutation
Mutation can be well explained using the genetic code
A)Point Mutation
1)Silent Mutation
2)Missense Mutation
3)Nonsense Mutation
B) Frame Shift Mutation

13. Silent Mutation
A mutation where a change in DNA sequence does not change the amino acid
sequence.
Missense Mutation
Missense mutation causing a single amino acid change in the protein sequence.
Nonsense Mutation
Nonsense mutation leading to pre mature stop codon formation, resulting in
truncated or nonfunctional proteins.

14. Mutation

15. Frame shift Mutation
Insertion or removal of a bases can change the reading frame with the resultant
incorporation of different amino acids.