Question

A common phrase used in biology is that "structure dictates function." Write this in your own words, and using the example of sickle cell anemia, explain how a single mutation can affect the function of red blood cells. This question requires knowledge of biological molecules and DNA/ RNA synthesis.

Answer 1

• Structure dictates function simply means that structure determines function.One fundamental concept of structure–function relationship is its sequence.The sequence determines the structure and the structrue performs the function.
• According to biology structure is mainly a three-dimensional shape of molecules and function is the activity that these molecules perform in chemical reactions, living cells and biochemical pathways.
• Structure in the terms of proteins can be a primary, secondary,tertiary and quaternary.Primary structure refers to the amino acid sequence of a protein.Secondary structure can be either of the forms; α-helices and β-sheets.Tertiary and quaternary structures is the final assembly of a protein and its the three-dimensional shape.
• A function is determined by a molecule’s three-dimensional shape or organization network.Let us take an example of this phrase.

Consider sickle cell anaemia:-

Sickle cell anaemia is an autosomal hereditary disease.It is due to the change in the shape of RBC due to the presence in them of a defective type of haemoglobin S.Tis disesae is manisfested only in homozygous recessive state (Hbs ,Hbs) Whereas the other forms Hba  and (Hbs , Hba)  is normal and carrier phenotype respectively.

The defect is caused by the substitution of Glutamic acid(Glu)by Valine(Val)at the sixth position of the  β-globin chain of the haemoglobin molecule.The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of  β-globin gene from GAG to GUG.Such that the shape of RBC changes to an elongated sickle shped in sturcture instead of a biconcave disc.