04 Molecular Basis of Inheritance - part 08 - Mutations and Genetic Code + t-RNA- the adapter molecule

04 Molecular Basis of Inheritance - part 08 - Mutations and Genetic Code + t-RNA- the adapter molecule


Mutations and Genetic Code: 
  • Mutation is a phenomenon in which sudden change in the DNA sequence takes place. It results in the change of genotype (i.e. character). 
  • Along with recombination, mutation is raw material for evolution as it also results in variations. 
  • During mutation, possibility of loss (deletion) or gain (insertion/ duplication) of a segment of DNA results in alteration in the chromosome. 
  • Mutation can also occur due to change in a single base pair of DNA. This is known as point mutation. 
  • Eg. Sickle cell anaemia .
  • Deletion or insertion of base pairs of DNA causes frame ­ shift mutations or deletion mutation. 
  • Insertion or deletion of one or two bases changes the reading frame from the point of insertion or deletion. 
  • Insertion or deletion of three or multiples of three bases (insert or delete) results in insertion or deletion of amino acids and reading frame remains unaltered from that point onwards.


t-RNA- the adapter molecule:

  • Scientists considered that there has to be a mechanism in which t-RNA will read the codon and 
  • Also simultaniously binds with the amino acid as amino acid does not have any special capacity to read the codon. 
  • So t-RNA is considered as an adapter molecule. This role of tRNA was understood much later.
  • Cloverleaf structure (2 dimentional) of t-RNA possess an anticodon loop that has bases complementary to the codon. It is calledanticodon. 
  • It shows amino acid acceptor end (3' end)having unpaired CCA bases (i.e. amino acid binding site) to which amino acid binds. 
  • For every amino acid, there is specific t- RNA. 
  • Initiator t-RNA is specific for methionine. There are no t-RNA's for stop codons. 
  • In the actual structure, the t-RNA molecule looks like inverted L (3 dimentional structure).

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