Question

Draw an illustration that shows how a mutation, change in DNA sequence, results in a change in either the expression of a protein OR a change in a protein's binding to a partner. Describe the flow of events or information illustrated in your drawing AND state how the mutation might result in a change in phenotype (a trait).

Answer 1

Changes in the sequence of nucleotides in an organism is called mutation. Nucleotide sequences code for aminoacids which make up proteins. The proteins function as enzymes and bring certain chemical reactions and bring certain physiological changes in the body. These physiological changes express as the phenotypes. So, any change in the nucleotide sequence will result in abnormal protein or non functional protein formed. These changes in proteins bring changes in the phenotype or the characters of the individuals.

One such mutation is seen causing sickle cell anemia. Here the mutation results in change in the aminoacid coded by the codons due to which the hemoglobin formed is slightly different in composition, which makes the RBCs sickle  shaped.

Here a change in the nucleotide "A" which is replaced by "T" of DNA results in the change in codon. Instead of CTC, the codon is CAC. Resulting in a different RNA codon where GAG becomes GUG. So instead of aminoaacid, glutamine, valine gets coded in the protein of hemoglobin. Glutamine is hydrophilic aminoacid. Valine is hydrophobic aminoacid. Due to the hydrophobic aminoacid replacing hydrophilic aminoacid, the linkages in the protein molecule gets effected in its tertiary structure. This results in hemoglobin getting crystallized and forming like rods when there is less O2 attached to it. Due to this the shape of the RBCs gets distorted becoming, sickel like. Such sickel shaped RBCs cant pass through narrow blood capillaries causing O2 deficiency in the tissues.

So a change in the nucleotide or mutation results in a disease which lasts for the whole life of the individual because it is genetic. So a normal hemoglobin which is soluble, gets converted in to crystalline form changing the shape of the RBCs.