Answer: The mRNA base that must be substituted is A. A is substituted by U.
Explanation: In the sixth position of the beta chain of hemoglobin, valine replaces glutamine acid. The effect of this substitution is an abnormal red blood cells with a sickle shape. Every amino acid is coded for by a least one codon. A codon is a triplet of nucleotides in a mRNA. The mRNA codons for glutamic acid are GAA and GAG, while the mRNA codons for valine are GUU, GUC, GUA and GUG.
When the base Adenine (A) in the mRNA codon GAG which codes for glutamic acid is substituted by the base Uracil (U), the new mRNA codon will be GUG which codes for valine.
The shrinking of a plant cell membrane away from the cell wall when placed in a hypertonic solution is called a plasmolysis... I don't know if that can be of any help :)
