Chemistry Chapter 10: Biomolecules

Chapter 10: Biomolecules

Key Topics: Carbohydrate Classification, Glucose Chemistry, Proteins & Zwitterion Structure, Nucleic Acids (DNA vs. RNA Base Pairing), and Vitamins & Enzymes.

1. Carbohydrates & Their Classification

Carbohydrates are optically active polyhydroxy aldehydes or ketones, or compounds that yield such units on hydrolysis.

Category Hydrolysis Behavior Examples
Monosaccharides Cannot be hydrolyzed further into simpler polyhydroxy aldehydes/ketones. Glucose, Fructose, Ribose
Oligosaccharides Yield 2 to 10 monosaccharide units on hydrolysis (e.g., Disaccharides). Sucrose, Lactose, Maltose
Polysaccharides Yield a large number of monosaccharide units on hydrolysis. Starch, Cellulose, Glycogen

2. Structure and Reactions of D-Glucose

Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) is an aldohexose and the most abundant carbohydrate in nature.

Action of Hydroiodic Acid (HI) - Straight Chain Proof: $$\text{CHO}-(\text{CHOH})_4-\text{CH}_2\text{OH} \xrightarrow{\text{Prolonged heating with HI}} \text{CH}_3-(\text{CH}_2)_4-\text{CH}_3 \ (\text{n-Hexane})$$
Reaction with Hydroxylamine ($\text{NH}_2\text{OH}$) - Carbonyl Group Proof: $$\text{CHO}-(\text{CHOH})_4-\text{CH}_2\text{OH} + \text{NH}_2\text{OH} \rightarrow \text{CH}=\text{N-OH}-(\text{CHOH})_4-\text{CH}_2\text{OH} \ (\text{Oxime})$$
Oxidation with Bromine Water ($\text{Br}_2\text{ water}$) - Aldehydic Group Proof: $$\text{CHO}-(\text{CHOH})_4-\text{CH}_2\text{OH} \xrightarrow{\text{Br}_2\text{ water}} \text{COOH}-(\text{CHOH})_4-\text{CH}_2\text{OH} \ (\text{Gluconic Acid})$$

3. Proteins, Amino Acids & Peptide Linkage

Proteins are high molecular mass polymers of $\alpha$-amino acids linked together by peptide bonds.

Zwitterionic Structure of Amino Acids: $$\text{H}_2\text{N-CHR-COOH} \rightleftharpoons \text{H}_3\text{N}^+-\text{CHR-COO}^- \ (\text{Zwitterion})$$ $$\text{In zwitterionic form, amino acid shows amphoteric behavior (reacts with both acids and bases).}$$
Peptide Bond Formation: $$-\text{COOH} + \text{H}_2\text{N}- \xrightarrow{-\text{H}_2\text{O}} -\text{CO-NH}- \ (\text{Peptide Linkage})$$

4. Nucleic Acids (DNA and RNA)

Nucleic acids are long-chain polymers of nucleotides responsible for the transmission of hereditary characteristics.

Feature DNA (Deoxyribonucleic Acid) RNA (Ribonucleic Acid)
Sugar Component $\beta$-D-2-deoxyribose $\beta$-D-ribose
Nitrogenous Bases Adenine (A), Guanine (G), Cytosine (C), Thymine (T) Adenine (A), Guanine (G), Cytosine (C), Uracil (U)
Base Pairing (Chargaff's Rule) $A = T$ (linked by 2 H-bonds), $G \equiv C$ (linked by 3 H-bonds) Usually single-stranded
Primary Function Carries genetic information from generation to generation. Protein synthesis in the cell.

5. Vitamins and Enzymes

  • Vitamins: Organic compounds required in small amounts for normal health and growth. Divided into Fat-soluble (Vitamins A, D, E, K) and Water-soluble (Vitamins B-complex and C).
  • Enzymes: Biocatalysts produced by living cells which are proteinaceous in nature. They are highly specific and efficient in catalyzing biochemical reactions.