STD 12th/ Ch-5/ What is point Mutation? Give one example.

 

A point mutation is a type of genetic mutation that involves a change in a single nucleotide, or building block, of DNA. Point mutations can occur spontaneously during DNA replication, or they can be induced by mutagens, such as chemicals or radiation. Point mutations can have various effects on the resulting protein, ranging from no effect at all to a complete loss of protein function.

 

Substitution mutations are the most common type of point mutation and involve the replacement of one nucleotide with another. 

Substitutions can occur in various ways, including:

 

Silent mutations: These occur when the substitution does not result in a change in the amino acid sequence of the protein. This is because of the degeneracy of the genetic code, where multiple codons can specify the same amino acid.

 

Missense mutations: These occur when the substitution results in a change in the amino acid sequence of the protein. Depending on the position of the substitution and the properties of the substituted amino acid, this can lead to a range of effects on protein function, from no effect to complete loss of function.

 

Nonsense mutations: These occur when the substitution results in a premature stop codon, which causes the protein to be truncated and often non-functional.

point mutation 

Insertion and deletion mutations involve the addition or removal of one or more nucleotides in the DNA sequence, respectively. These types of mutations can have more significant effects on protein function than substitution mutations, as they can cause frameshifts, where the reading frame of the genetic code is disrupted, resulting in a completely different amino acid sequence downstream of the mutation.

 

Example: Point mutation is the substitution mutation that causes sickle cell anemia. This condition is caused by a single nucleotide substitution in the beta-globin gene, where the codon that specifies glutamic acid is changed to a codon that specifies valine. This substitution affects the structure of the hemoglobin protein, causing it to form abnormal red blood cells that are sickle-shaped and less able to carry oxygen. As a result, individuals with sickle cell anemia experience a range of symptoms, including anemia, pain, and organ damage.

In summary, point mutations are genetic mutations that involve the alteration of a single nucleotide in the DNA sequence, and can have various effects on protein function depending on the type and location of the mutation.

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