Mutations in DNA | Anatomy2Medicine
DNA Mutations

Mutations in DNA


  • Mutations in DNA


    • Severity of damage: silent << missense < nonsense < frameshift.
    • For silent, missense, and nonsense mutations:
      • Transitionpurine to purine (e.g., A to G) or pyrimidine to pyrimidine (e.g., C to T).
      • Transversionpurine to pyrimidine (e.g., A to T) or pyrimidine to purine (e.g., C to G).


  • Silent


      • Nucleotide substitution but codes for same (synonymous) amino acid
      • often base change in 3rd position of codon (tRNA wobble).


  • Missense
  • Nucleotide substitution resulting in changed amino acid


      • called conservative if new amino acid is similar in chemical structure


  • Sickle cell disease
  • Nonsense
  • Nucleotide substitution resulting in early stop codon.


      • Stop the nonsense!


  • Frameshift
  • Deletion or insertion of a number of nucleotides not divisible by 3, resulting in misreading of all nucleotides downstream, usually resulting in a truncated, nonfunctional protein.
  • Duchenne muscular dystrophy


Exam MCQ

Silent mutation   is mostly likely to result from:

A  Substitution of the first base of codon

B  Substitution of the third  base of codon

C  Conversion of a nonsense codon into a sense codon

D  Conversion of a sense codon into a nonsense codon

Ans B

Exam MCQ

Amino acid sequence of the encoded protein is not changed in:

A  Silent mutation

B  Acceptable mis-sense mutation

C  Both of the above

D  Neither of the above

Ans A

Exam MCQ

Haemoglobin S is an example of a/an:

A  Silent mutation

B  Acceptable mis-sense mutation

C   Unacceptable mis-sense mutation

D  Partially Acceptable mis-sense mutation

Ans D

Exam MCQ

If the codon UAC on mRNA changes into UAG as a result of  a base substitution in DNA, it will result in:

A  Silent mutation

B  Acceptable mis-sense mutation

C  Nonsense mutation

D  Frameshift mutation

Ans C

Exam MCQ

Insertion of a base in a gene can cause

A  Charge in reading frame

B  Garbled amino acid sequence in the encoded protein

C  Premature termination  of translation

D  All the above

Ans D

Exam MCQ

A frameshift mutation changes reading frame beacause the genetic code:

A  Is degenerate

B  Is overlapping

C  Has no punctuations

D  Is universal

Ans C