Molecular Basis of Mutation

Mutation is a type of change that occurs in our DNA sequence, either by mistake or due to any environmental factors like UV light and cigarette smoke. Mutation which occurs by mistake is known as spontaneous  mutation and the mutation which occurs due external factors are called induced mutation. Induced mutation generally occurs at higher frequency than spontaneous mutation. Mutation mainly occurs because of chemical instability of purine and pyrimidine bases and this leads to change in DNA sequence.


Gene Mutation

Gene mutation is a change in DNA sequence because of instability in purine and pyrimidine base pairs. This sequence differs from the sequence which is found in most humans. Mutation disrupts normal development in the body, there are so many genetic disorders which happen due to gene mutation like blood cancer, skin cancer, etc and apart from this they also alter the function of essential protein, by changing gene instruction for making protein.


Types of Mutation

There are several types of Mutation occurring due to abnormal factors and they are:

  1. Missense Mutation: Under this type of mutation there is change in one DNA base pair which leads to substitution of one amino acid from another in the protein made by the gene. 

  2. Nonsense Mutation: Under this mutation also there is a change in one DNA base pair but here instead of substitution of one amino acid from another, alteration of DNA sequence happens which stops synthesis of protein. This mutation leads to shortage in protein.

  3. Insertion or Deletion:  Under this mutation there is an addition of the number of DNA bases in a gene by adding a piece of DNA, whereas  deletion removes a piece of DNA. It can be of a single base pair or of a large section of base pair, in both cases they affect the function of protein.

  4. Duplication: Under this mutation duplication of a piece of DNA happens abnormally  and they form a number of copies, one or more than one time. 

  5. Frameshift Mutation:  Under this type of mutation there is an addition or loss of DNA bases that changes a gene reading frame. A reading frame consists of groups of 3 bases and each base code for  one amino acid. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein is usually nonfunctional.

Insertions, deletions, and duplications all can be called as frameshift mutations.

InRepeat expansion:  Under this type of mutation nucleotide repeats are short DNA sequences that are repeated a number of times in a row.


Causes of Mutation

There are so many reasons for mutation to occur

  1. When DNA fails to copy properly. For example, when a cell divides, it makes a copy of its DNA — and sometimes the copy is not that much perfect and this makes a small difference from the original DNA sequence. 

  2. External factors can also cause mutation example UV- rays they cause DNA to break down and lead to abnormalities like cancer.


Advantage and Disadvantage of Mutation

 Advantage

  1. Mutations in many bacteria result in antibiotic-resistant strains of bacteria that can survive in the presence of antibiotics.

  2. Few mutations lead to a new form of protein which helps organisms to adapt with changes of environment.

Disadvantage

  1. They cause genetic disorders. Example: Cystic fibrosis.

  2. Cancer is another disease caused by mutation.

 

MCQ Based on Mutation

1. How many kinds of mutation are there in DNA which includes mutation of only one base?

a) 1

b) 2

c) 3

d) 4

Answer: (b)

2. The Mutation occurs at a random basis within a Genome.

a) True

b) False

Answer: (a)

3. By which Enzyme does E.coli tag its parental DNA strand?

a) Methylase

b) Polymerase

c) Phosphorylase

d) Acetylase

Answer: Methylase

4.  High level of Mutation in the Germ cells is acceptable but in Somatic cells can be Catastrophic.

a) True

b) False

Answer: (b)

5. Point  Mutation involves.

a) insertion

b)deletion

c)duplication

Answer: (a)

6. X-rays causes Mutation by.

a) insertion

b)deletion

c)duplication

Answer: (b)

7. Which of the following is not Ionising Radiation.

a)X-ray

b) UV-rays

c) alpha rays

Answer: (b)

FAQ (Frequently Asked Questions)

1. Define Mutation?

Ans. Mutation is a process under which there is a change in the structure of genes which results in various abnormalities in our body. And the agents which cause mutation are known as mutants. There are both external and internal factors which lead to mutation.

2. How many types of mutation are there based on causing factors?

Ans. Based on factor Mutation is of two types:

  1. Induced Mutation: Mutation which occurs due external factors are called induced mutation. External factors are harmful UV-rays, direct sunlight, etc.

  2. Spontaneous Mutation: Mutation which occurs by mistake is known as spontaneous  mutation.

3. Explain different types of Mutation?

Ans. Different types of mutation are:

  • Silent Mutation

A change or variations within the sequence of nucleotide bases which constitutes DNA, without a subsequent change in the amino acids or the function of the overall protein.

  • Nonsense Mutation

A nonsense mutation occurs when there is a change in the sequence of nucleotides and holds the normal sequence of amino acids in the final protein.

  • Missense Mutation

 It is a type of point mutation, where two different amino acids are placed within the produced protein, other than its original.

4. What are the causes of Mutation?

Ans. Cause of mutation can be of two types either internal or external. Internal cause includes sudden change in base pair due to abnormal internal activities of the body,all these mutations lead to evolution and external cause include factors like UV-rays which leads to change in DNA sequence.

5. What is Frameshift Mutation?

Ans. Under this type of mutation there is an addition or loss of DNA bases that changes a gene reading frame. A reading frame consists of groups of 3 bases that each code for one amino acid.