CBSE Class 12 Chemistry Notes: Biomolecules – Important Question for Boards

Prob 1.  In E. coli DNA, the AT/GC ratio is 0.93. If the number of moles of adenine in the DNA sample is 558,000, calculate the number of moles of guanine present

Sol.   Number of moles of adenine must be equal to that of thymine

(A + T) = 558,000 + 558,000 = 1116000

Since (A + T)/(C + G ) = 0.93

Therefore, no of moles of C + G

C + G =

Since number of moles of C = number of moles of G

Number of moles of guanine =

Prob 2.  How will you synthesize alanine from acetylene?

Sol.

Prob 3.  Write the structure of alanine at pH =2 and pH = 10.

Sol.  Amino acids exist as zwitter ions (I) in aqueous solution. In presence of acids (pH=2) basic COO^– accepts a proton to give cation (II) but in presence of base (pH = 10), the acidic  donates a proton to the base and thus exists as anion (III).

Prob 4.  Glycine exists as (H₃N⁺CH₂COO^–) while anthranilic acid (P–NH₂C₆H₄– COOH) does not exist as dipolar ions. 

 Sol.  – COOH is too weakly acidic to transfer H⁺ to the weakly basic – NH₂ attached to the electron withdrawing benzene ring. When attached to an aliphatic carbon, the – NH₂ is sufficiently basic to accept H⁺ from – COOH group

 Prob 5. nCF₂ = CF₂  (–CF₂ – CF₂ –)_n Teflon

 Sol.  A = (NH₄)₂S₂O₈

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