Biology · Class 11 Science

Ch 6Biomolecules — Class 11 Biology, concept-first.

Biochemistry is the branch of biology that studies the chemical composition of living cells and the chemical reactions and molecular changes that occur in plants, animals and micro-organisms. It gives us the molecular basis for cell communication, and for the chemistry of inheritance and of disease.

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Biomolecules and Macromolecules

A living cell's chemistry is built almost entirely from just a handful of elements — the prime elements carbon, hydrogen and oxygen (drawn largely from air and water), the macro elements nitrogen, phosphorus, potassium,…

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Introduction to Biomolecules

Biochemistry is the branch of biology that studies the chemical composition of living cells and the chemical reactions and molecular changes that occur in plants, animals and micro-organisms.

Biomolecules in the Cell

Life on Earth spans an enormous range of forms -- from unicellular organisms such as bacteria and yeast to complex multicellular plants and animals -- yet every one of them is built from cells as thei…

Carbohydrates

The word carbohydrate literally means 'hydrate of carbon'; carbohydrates are also called saccharides. They are built from just three elements — carbon, hydrogen and oxygen — with the general formula C…

Monosaccharides

Monosaccharides are the simplest carbohydrates — crystalline, sweet-tasting, water-soluble molecules that cannot be split (hydrolysed) into any smaller carbohydrate unit.

Disaccharides

Free monosaccharides are actually rare in nature — most of the sugar found in living organisms exists combined as disaccharides.

Polysaccharides

When a chain of monosaccharide units keeps growing — one condensation reaction after another adding a further sugar unit to the chain — the result is a very large molecule called a polysaccharide; thi…

Lipids

Lipids are a chemically diverse group of substances with a greasy consistency, built around long hydrocarbon chains and containing carbon, hydrogen and oxygen — but, unlike carbohydrates, with a hydro…

Simple Lipids

Simple lipids are esters of fatty acids with various alcohols; fats and waxes are the two main kinds.

Compound Lipids

Compound lipids are esters of fatty acids that carry, in addition, some other chemical group — phosphate in the case of phospholipids, a sugar in the case of glycolipids.

Sterols

Sterols are derived lipids — built not directly from glycerol and fatty acids but by further modification, and structurally quite different from the other lipid classes.

Proteins

The term 'protein' comes from the Greek proteios, meaning 'first' or 'of primary importance' — a name suggested by the chemist Berzelius in 1830.

Classification of Proteins

On the basis of their structure, proteins are grouped into three classes:

Nucleic Acids

The nucleic acids are, along with proteins, among the largest molecules found in living cells; every nucleotide of a nucleic acid is built from three components: a five-carbon sugar, phosphoric acid,…

Structure of DNA

DNA is an extremely long chain built from alternating sugar and phosphate units. The sugar is always deoxyribose, and it is always linked to the phosphate group in the same way, so the backbone repeat…

Ribonucleic Acid (RNA)

Ribonucleic acid (RNA) is the other nucleic acid found in living cells. Unlike DNA, it is not usually the hereditary material — though in certain organisms, such as the tobacco mosaic virus, RNA does…

Enzymes

At any given moment, a living cell is quietly running thousands of different chemical reactions simultaneously, at ordinary body temperature — something that would be impossible without enzymes.

Properties of Enzymes

Enzymes share several defining properties:

Nature of Enzymes

On the basis of their chemical composition, enzymes fall into two categories: purely proteinaceous enzymes, which are made of protein alone (e.g.

Nomenclature of Enzymes

Enzymes can be named in several different ways.

Classification of Enzymes

Enzymes are grouped into six major classes according to the general type of reaction they catalyse:

Mechanism of Enzyme Action

The basic mechanism by which an enzyme catalyses a reaction starts with the substrate (or substrates) binding to the enzyme's active site — the specific region of the enzyme surface shaped to combine…

Factors Affecting Enzyme Activity

The rate of an enzyme-catalysed reaction is governed by several factors:

Concept of Metabolism

Metabolism is the sum total of all the chemical reactions occurring within every cell of a living organism — reactions that both supply the energy needed for the organism's vital processes and provide…

Secondary Metabolites

Secondary metabolites (SMs) are small organic molecules produced by an organism that — unlike primary metabolites such as carbohydrates, lipids, proteins and nucleic acids — are not strictly essential…

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