Biomolecules Class 11 Biology PDF Notes

01
Introduction to biomolecules class 11 biology pdf

Are you searching for a comprehensive biomolecules class 11 biology pdf to ace your medical entrance exams? Biomolecules are the organic and inorganic compounds present in living organisms that facilitate the chemical processes of life. From providing energy through sugars to carrying genetic codes in DNA, these molecules form the molecular logic of biological systems. For NEET aspirants, understanding the distinction between micromolecules and macromolecules is the first step toward mastering this high-yield chapter.

In this guide, we dive deep into the structural and functional diversity of life’s building blocks. Whether you are analyzing the primary structure of proteins or calculating the rate of enzyme-catalyzed reactions, this biomolecules class 11 biology pdf summary covers every NCERT line essential for your preparation.

MICROMOLECULES Low molecular weight compounds (18–800 Daltons) found in the acid-soluble pool. Examples: Amino acids, simple sugars, lipids.

MACROMOLECULES High molecular weight polymers (above 10,000 Daltons) found in the acid-insoluble fraction. Examples: Proteins, Polysaccharides, Nucleic acids.

02
Methods to Study Cellular Composition

To analyze the chemical composition of living tissue, scientists use biochemical fractionation. A living tissue (like liver or leaf) is ground in Trichloroacetic acid (Cl₃CCOOH) using a mortar and pestle to create a thick slurry. Upon filtration, two distinct fractions are obtained: the Filtrate (Acid-soluble pool) and the Retentate (Acid-insoluble fraction).

Fraction	Molecular Weight	Contents
Acid-Soluble Pool	18 – 800 Da	Amino acids, Monosaccharides, Nucleosides, Inorganic ions
Acid-Insoluble Fraction	> 10,000 Da	Proteins, Polysaccharides, Nucleic acids, Lipids

TIP

Even though Lipids have a molecular weight of less than 800 Da, they appear in the acid-insoluble fraction because they form large vesicles when tissues are ground, which are too big to pass through the filter.

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03
Primary and Secondary Metabolites

In your biomolecules class 11 biology pdf study, you must distinguish between metabolites that have identifiable functions in host physiological processes and those whose roles are primarily ecological.

Primary Metabolites: Directly involved in growth and development (e.g., carbohydrates, amino acids).
Secondary Metabolites: Not directly involved in primary life functions but important for defense or attraction. Examples: Alkaloids (Morphine), Terpenoids, Essential oils, and Lectins (Concanavalin A).

04
Proteins: The Workhorses of the Cell

Proteins are linear polymers of amino acids linked by Peptide bonds. They are heteropolymers because they are made of 20 different types of amino acids. Collagen is the most abundant protein in the animal world, while RUBISCO is the most abundant protein in the whole biosphere.

AMINO ACID GENERAL STRUCTURE

NH₂ — CH(R) — COOH

Levels of Protein Structure

Protein architecture is organized into four levels, which is a favorite topic in the biomolecules class 11 biology pdf exam questions:

PRIMARY The sequence of amino acids. Tells us the positional information of every residue.

SECONDARY Folding into patterns like α-helix or β-pleated sheets, stabilized by H-bonds.

TERTIARY Overall 3D folding of the polypeptide chain into a globular shape. Necessary for biological activity.

QUATERNARY Architecture of complex proteins consisting of more than one polypeptide subunit (e.g., Hemoglobin).

05
Polysaccharides and Carbohydrates

Polysaccharides are long chains of sugars linked by Glycosidic bonds. Starch (plants) and Glycogen (animals) serve as storage houses for energy. Cellulose, found in plant cell walls, is a homopolymer of glucose units.

SUGAR REDUCING PROPERTY

Right end of a polysaccharide is the reducing end; Left end is non-reducing.

WARN

Starch can hold I₂ molecules in its helical structure, giving a blue-black color. Cellulose has no such helical structure and thus cannot hold Iodine.

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06
Nucleic Acids: The Genetic Blueprint

Nucleic acids are polymers of Nucleotides. Each nucleotide consists of a heterocyclic nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group. DNA and RNA are the two types of nucleic acids found in living systems.

NUCLEOSIDE Nitrogenous Base + Pentose Sugar. (e.g., Adenosine, Guanosine).

NUCLEOTIDE Nucleoside + Phosphate group. (e.g., Adenylic acid, Guanylic acid).

Structure of DNA

Proposed by Watson and Crick, DNA is a double helix consisting of two antiparallel strands. Adenine pairs with Thymine (2 H-bonds) and Guanine pairs with Cytosine (3 H-bonds). One full turn of the helix is 34 Å long and contains 10 base pairs.

07
Enzymes: Biological Catalysts

Almost all enzymes are proteins. They accelerate metabolic reactions by lowering the Activation Energy required for the reaction to proceed. Enzymes are highly specific and exhibit maximum activity at optimal temperature and pH levels.

REACTION RATE RATIO

Rate doubled/halved for every 10°C change in temperature.

Factors Affecting Enzyme Activity

Temperature & pH: Activity is highest at “optima”; decreases above or below this range.
Substrate Concentration: Rate increases with concentration until all active sites are saturated (V_max).
Inhibition: Competitive inhibitors compete with the substrate for the active site (e.g., Malonate inhibits Succinate dehydrogenase).

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Quick Revision Summary

Amino Acids: Amphoteric molecules with −NH₂ and −COOH groups.
Peptide Bond: Formed by dehydration between carboxyl and amino groups.
Collagen: Ground substance of connective tissues.
Bonds: Glycosidic (sugars), Peptide (proteins), Phosphodiester (nucleic acids), Ester (lipids).
Zwitterion: State of amino acid at specific pH where it has both + and – charges.
Prosthetic Groups: Organic cofactors tightly bound to the apoenzyme (e.g., Heme in peroxidase).
Co-enzymes: Organic cofactors transiently bound (e.g., NAD, NADP containing Niacin).
Lyases: Enzymes that remove groups without hydrolysis.
Ligases: Enzymes that catalyze the linking of two molecules.
Chitin: Complex polysaccharide found in fungal cell walls and arthropod exoskeletons.

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08
Frequently Asked Questions

Why are lipids considered macromolecules despite their low weight?

Lipids are not strictly macromolecules (polymers). However, they are found in the acid-insoluble fraction because they form part of cell membranes. When tissue is disrupted, membranes break into pieces and form water-insoluble vesicles that are caught on the filter.

What is a competitive inhibitor in enzyme kinetics?

A competitive inhibitor resembles the substrate in molecular structure and competes for the enzyme’s active site. This decreases the enzyme’s affinity for the substrate, increasing the K_m but leaving V_max unchanged.

Explain the concept of an apoenzyme and holoenzyme.

An apoenzyme is the protein part of an enzyme which is inactive. A cofactor is a non-protein component required for activity. When the apoenzyme and cofactor are joined, they form the functional, active enzyme called a Holoenzyme.

What defines a “secondary metabolite”?

Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. They often play roles in ecological interactions, such as defense chemicals against predators.

How do nucleic acids differ from proteins structurally?

Proteins are polymers of amino acids linked by peptide bonds, whereas nucleic acids are polymers of nucleotides linked by 3’—5′ phosphodiester bonds. Proteins have a vast variety of functions (structural, enzymatic), while nucleic acids primarily store and transmit genetic data.

What is the significance of the B-DNA structure?

B-DNA is the most common form of DNA under physiological conditions. It is a right-handed helix with a pitch of 3.4 nm and a diameter of 2 nm. Understanding this structure is key to explaining DNA replication and transcription mechanisms.

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Table of Contents — Biology Class 11

Biology — Class 11

01	The Living World	Go to page
02	Biological Classification	Go to page
03	Plant Kingdom	Go to page
04	Animal Kingdom	Go to page
05	Morphology of Flowering Plants	Go to page
06	Anatomy of Flowering Plants	Go to page
07	Structural Organisation in Animals	Go to page
08	Cell: The Unit of Life	Go to page
09	Biomolecules	Go to page
10	Cell Cycle and Cell Division	Go to page
11	Photosynthesis in Higher Plants	Go to page
12	Respiration in Plants	Go to page
13	Plant Growth and Development	Go to page
14	Breathing and Exchange of Gases	Go to page
15	Body Fluids and Circulation	Go to page
16	Excretory Products and their Elimination	Go to page
17	Locomotion and Movement	Go to page
18	Neural Control and Coordination	Go to page
19	Chemical Coordination and Integration	Go to page

Biomolecules Class 11 Biology PDF: The Ultimate NEET Revision Guide

01
Introduction to biomolecules class 11 biology pdf

02
Methods to Study Cellular Composition

03
Primary and Secondary Metabolites