Biomolecules NEET Cheat Sheet: Everything You Need
Biomolecules·2 min read·NEET 2026
What NEET Asks
Key Focus: Classification, structures, chemical reactions (hydrolysis, denaturation), and biological functions of carbohydrates, proteins, and nucleic acids.
Question Type: Typically 2-3 questions per year, often involving structural identification, linkage types, or functional implications.
Marks Weightage: 8-12 marks, making it a high-scoring chapter.
Key Points
Carbohydrates: Polyhydroxy aldehydes or ketones. Classified as monosaccharides (e.g., glucose, fructose), oligosaccharides (e.g., sucrose, lactose), and polysaccharides (e.g., starch, cellulose). Glycosidic linkage connects units. Reducing sugars have a free aldehyde/ketone group.
Proteins: Polymers of α-amino acids linked by peptide bonds. Essential amino acids are obtained from diet. Four levels of structure: primary (sequence), secondary (α-helix, β-pleated sheet), tertiary (3D folding), quaternary (multiple subunits). Denaturation disrupts higher structures.
Nucleic Acids: DNA and RNA. Polymers of nucleotides (base + sugar + phosphate). Bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T) in DNA; Uracil (U) in RNA instead of T. Phosphodiester linkage connects nucleotides.
Must-Know Formula / Reaction
Peptide Bond Formation:
R-CH(NH₂)−COOH + R'−CH(NH₂)−COOH → R-CH(NH₂)−CO−NH−CH(R')−COOH + H₂O
-CO-NH-: The amide linkage formed between the carboxyl group of one amino acid and the amino group of another, releasing water.
Common Mistakes
Students often confuse reducing and non-reducing sugars; sucrose is non-reducing because its anomeric carbons are involved in the glycosidic linkage.
Don't confuse the bases: Uracil is in RNA, Thymine in DNA. A & G are purines; C, T, U are pyrimidines.
Forgetting that primary structure (peptide bonds) remains intact during protein denaturation, as it involves covalent bonds.
Rapid Revision
Carbohydrates (energy), Proteins (structure/enzymes), Nucleic Acids (genetic info) are vital biomolecules. Memorize their building blocks (monosaccharides, amino acids, nucleotides), key linkages (glycosidic, peptide, phosphodiester), and structural distinctions (anomers, essential amino acids, DNA vs RNA base/sugar differences).
Frequently Asked Questions
What is the main function of carbohydrates in living organisms?▾
Carbohydrates primarily serve as the main source of energy for living organisms. They also play structural roles, like cellulose in plant cell walls, and are involved in cell recognition processes.
What is protein denaturation and what causes it?▾
Protein denaturation is the process where a protein loses its specific three-dimensional structure (secondary, tertiary, and quaternary) without breaking its primary structure (peptide bonds). It is caused by changes in pH, temperature, or exposure to certain chemicals like heavy metal salts or organic solvents.
What are the key differences between DNA and RNA?▾
DNA contains 2'-deoxyribose sugar and thymine (T) as a pyrimidine base, forming a double-stranded helix. RNA contains ribose sugar and uracil (U) instead of thymine, and is generally single-stranded. Both carry genetic information, but DNA is the primary genetic material in most organisms.
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