Q.What is point mutation? Give one example.

A point mutation is a type of gene mutation that involves a change in a single base pair of DNA. This alteration in a single nucleotide can lead to a change in the corresponding codon, which in turn might result in the incorporation of a different amino acid during protein synthesis, or even a premature stop codon.

A classic example is sickle cell anemia. In this genetic disorder, a single base substitution occurs in the coding-strand DNA of the beta-globin gene. Specifically, at the sixth codon, the base adenine (A) is replaced by thymine (T), changing the codon from GAG to GTG. This is transcribed into the mRNA codon GUG instead of GAG, leading to the substitution of glutamic acid by valine at the six …

Our genetic information, the blueprint for life, is meticulously stored in DNA. This DNA is made up of a sequence of chemical units called nucleotides, each containing one of four bases: Adenine (A), Guanine (G), Cytosine (C), or Thymine (T). The precise order of these bases dictates the instructions for building proteins, which carry out most of the functions in our bodies.

Sometimes, however, errors can occur in this genetic blueprint. A mutation refers to any sudden, heritable change in the genetic material of an organism. These changes can range from large-scale alterations in chromosomes to very subtle modifications within a single gene.

A point mutation is a specific type of mutation characterized by a change in just a single base pair of DNA. Imagine a long sentence where changing just one letter can completely alter the meaning of a word, or even the entire sentence. Similarly, a single base change in DNA can have significant consequences for the organism.

These single base pair changes can occur in a few ways:

• Substitution: One base is replaced by another. For example, an Adenine (A) might be replaced by a Guanine (G), or a Cytosine (C) by a Thymine (T).
• Insertion: An extra base is added into the DNA sequence.
• Deletion: A base is removed from the DNA sequence.

When a substitution, insertion, or deletion of a single base occurs, it can alter the "reading frame" of the genetic code, especially in the case of insertions and deletions. Since DNA is read in triplets of bases (codons), adding or removing a single base shifts all subsequent codons, potentially leading to a completely different sequence of amino acids in the resulting protein. A substitution, on the other hand, might change only one amino acid, or sometimes, due to the redundancy of the genetic code, might not change the amino acid at all.

A classic and well-understood example of a point mutation is sickle cell anemia. This genetic disorder illustrates how a single base change can lead to a severe disease.

In individuals with sickle cell anemia, there is a specific point mutation in the gene that codes for the beta-globin chain of hemoglobin. Hemoglobin is the protein in red blood cells responsible for carrying oxygen throughout the body.

Here's what happens at the molecular level:

• At the sixth codon of the beta-globin gene, a single base substitution occurs on the coding (sense) strand of the DNA — the strand that reads the same as the mRNA, with T in place of U. …

A useful contrast is to compare a point mutation against a frameshift mutation: a substitution point mutation (like the one in sickle cell anaemia) changes at most one amino acid because the reading frame stays intact, whereas an insertion or deletion of a single base shifts every codon downstream of it, usually garbling the entire rest of the protein. Seeing why …