Question

Answer the following case-based questions on biomolecules: \[ (a)\;\text{Write the name of basic building units of proteins and nucleic acids. How can you differentiate between fibrous and globular proteins on the basis of their structures?} \] \[ (b)(i)\;\text{What products would be formed when a nucleotide from DNA containing thymine is hydrolyzed?} \] OR \[ (b)(ii)\;\text{Write one structural difference between DNA and RNA.} \] \[ (c)\;\text{Give one example each of a fat-soluble vitamin and a water-soluble vitamin.} \]

Hint:

Nucleotide = nitrogenous base + sugar + phosphate group. Protein = polymer of amino acids.

Answer 1

Concept:
Biomolecules are large molecules present in living systems. Proteins, carbohydrates, nucleic acids, lipids and vitamins are important biomolecules. Proteins are polymers of amino acids, while nucleic acids are polymers of nucleotides.

Step 1: Basic building unit of proteins.
Proteins are formed by the joining of many \(\alpha\)-amino acids through peptide bonds. Therefore: \[ \text{Basic unit of proteins}=\alpha\text{-amino acids} \]

Step 2: Basic building unit of nucleic acids.
Nucleic acids such as DNA and RNA are polymers of nucleotides. Each nucleotide contains: \[ \text{Nitrogenous base}+\text{Pentose sugar}+\text{Phosphate group} \] Therefore: \[ \text{Basic unit of nucleic acids}=\text{Nucleotides} \]

Step 3: Differentiate fibrous and globular proteins.
Fibrous proteins have long thread-like or fibre-like structures. Their polypeptide chains are arranged parallel to each other. They are generally insoluble in water. Examples: Keratin, Collagen Globular proteins have compact, folded and nearly spherical structures. Their polypeptide chains are folded into ball-like shapes. They are generally soluble in water. Examples: Insulin, Albumin \[ \begin{array}{|c|c|} \hline \textbf{Fibrous proteins} & \textbf{Globular proteins}\\ \hline \text{Long fibre-like structure} & \text{Compact spherical structure}\\ \hline \text{Polypeptide chains run parallel} & \text{Chains are folded into globular shape}\\ \hline \text{Generally insoluble in water} & \text{Generally soluble in water}\\ \hline \text{Example: Keratin} & \text{Example: Insulin}\\ \hline \end{array} \]

Step 4: Hydrolysis of DNA nucleotide containing thymine.
A nucleotide from DNA containing thymine has three components: \[ \text{Thymine}+\text{Deoxyribose sugar}+\text{Phosphate group} \] On hydrolysis, it gives: \[ \text{Thymine}+\text{Deoxyribose sugar}+\text{Phosphoric acid} \]

Step 5: Structural difference between DNA and RNA.
DNA contains deoxyribose sugar. RNA contains ribose sugar. Also, DNA contains thymine, whereas RNA contains uracil. One structural difference is: DNA has deoxyribose sugar, while RNA has ribose sugar.

Step 6: Examples of vitamins.
Fat-soluble vitamins include: Vitamin A, D, E, K Water-soluble vitamins include: Vitamin B-complex and Vitamin C Therefore: Fat-soluble vitamin: Vitamin A Water-soluble vitamin: Vitamin C Hence: Proteins are made up of \(\alpha\)-amino acids and nucleic acids are made up of nucleotides. A DNA nucleotide containing thymine gives thymine, deoxyribose sugar and phosphoric acid on hydrolysis. DNA contains deoxyribose sugar whereas RNA contains ribose sugar. Vitamin A is fat-soluble and Vitamin C is water-soluble.