Schooling · Class 11 · Biology · Biomolecules · Chapter on a page
CBSE Class 11 · Biology · NCERT Biology
Biomolecules: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- Living tissue contains both organic…
- Carbohydrates are made of carbon…
- Proteins are polymers of amino acids
- Lipids are fats and fat-like…
- Nucleic acids (DNA and RNA) store…
- Enzymes are biological catalysts
- Primary, secondary, tertiary and…
- Formulas and facts
- General formula for monosaccharides
- Peptide bond formation
- Glycosidic bond
- Phosphodiester bond
- Lock and key model of enzyme action
- Induced fit model
- Optimum temperature and pH
- Worked examples
- Identifying the type of carbohydrate
- Counting peptide bonds
- Effect of temperature on enzyme…
- Watch out for
- Thinking all carbohydrates taste sweet
- Confusing peptide bonds with…
- Believing enzymes are used up in…
- Assuming all proteins are enzymes
- Thinking high temperature always…
What this chapter is about
This chapter introduces you to the chemical compounds that make up living organisms. All life, from bacteria to banyan trees to humans, is built from the same basic types of molecules: carbohydrates, proteins, lipids and nucleic acids. You will learn what these biomolecules are made of, how they are structured, and what roles they play in cells.
Key ideas
- Living tissue contains both organic and inorganic compounds. Organic compounds contain carbon and include carbohydrates, proteins, lipids and nucleic acids. Inorganic compounds include water and mineral ions.
- Carbohydrates are made of carbon, hydrogen and oxygen in the approximate ratio C:H:O = 1:2:1. Simple sugars (monosaccharides) like glucose and fructose join to form disaccharides (sucrose, maltose) and polysaccharides (starch, cellulose, glycogen).
- Proteins are polymers of amino acids joined by peptide bonds. There are about 20 different amino acids in living systems. The sequence and folding of amino acids determine a protein's shape and function.
- Lipids are fats and fat-like substances that are insoluble in water but soluble in organic solvents. They include triglycerides (fats and oils), phospholipids (in cell membranes) and steroids (like cholesterol).
- Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides. Each nucleotide has a nitrogenous base, a pentose sugar and a phosphate group.
- Enzymes are biological catalysts that lower the activation energy of reactions. They are highly specific and are affected by temperature, pH and substrate concentration.
- Primary, secondary, tertiary and quaternary structures describe the levels of protein organisation, from the amino acid sequence to the arrangement of multiple polypeptide chains.
Formulas and facts to remember
- General formula for monosaccharides: (CH₂O)ₙ, where n is typically 3 to 7. For glucose, n = 6, giving C₆H₁₂O₆.
- Peptide bond formation: When two amino acids join, the –COOH group of one reacts with the –NH₂ group of another, releasing one molecule of water. This is a condensation or dehydration reaction.
- Glycosidic bond: The bond that joins monosaccharides to form di- or polysaccharides, also formed by condensation.
- Phosphodiester bond: The bond linking nucleotides in nucleic acids, connecting the phosphate of one nucleotide to the sugar of the next.
- Lock and key model of enzyme action: The substrate fits exactly into the active site of the enzyme, like a key fits a lock.
- Induced fit model: The enzyme's active site changes shape slightly when the substrate binds, improving the fit.
- Optimum temperature and pH: Each enzyme works best at a specific temperature and pH. Human enzymes typically have an optimum around 37 °C.
- Cofactors and coenzymes: Non-protein components that help enzymes function. Cofactors are usually metal ions (Zn²⁺, Mg²⁺); coenzymes are organic molecules often derived from vitamins.
Common mistakes
- Thinking all carbohydrates taste sweet → Only simple sugars (monosaccharides and some disaccharides) taste sweet; polysaccharides like starch and cellulose do not.
- Confusing peptide bonds with glycosidic bonds → Peptide bonds join amino acids in proteins; glycosidic bonds join sugars in carbohydrates.
- Believing enzymes are used up in reactions → Enzymes are catalysts and are released unchanged after each reaction cycle; they can be reused.
- Assuming all proteins are enzymes → Many proteins have structural, transport or regulatory roles (like collagen, haemoglobin, hormones) and are not enzymes.
- Thinking high temperature always increases enzyme activity → Beyond the optimum, enzymes denature and lose function permanently.
Quick revision
- Carbohydrates: monosaccharides → disaccharides → polysaccharides; joined by glycosidic bonds.
- Proteins: amino acids joined by peptide bonds; structure levels are primary, secondary, tertiary, quaternary.
- Lipids: fats (energy storage), phospholipids (membranes), steroids (signalling); insoluble in water.
- Nucleic acids: nucleotides (base + sugar + phosphate) joined by phosphodiester bonds; DNA stores genetic information, RNA helps express it.
- Enzymes: biological catalysts; specific; affected by temperature, pH and inhibitors; work by lowering activation energy.