Biomolecules Complete Chapter Revision For NEET by PW

Biomolecules are chemical compounds found in living organisms that support cellular structure and life processes. Proteins, carbohydrates, lipids, nucleic acids, and other small molecules participate in energy production, information storage, growth, and metabolism. Understanding their structures and functions helps explain how cells perform essential biological activities.

For NEET, this chapter requires a clear understanding of NCERT definitions, biomolecule classification, chemical analysis, amino acids, protein structure, carbohydrate linkages, nucleotides, and enzyme activity. PW supports NEET preparation through live and recorded classes, study material, practice questions, and mock tests to help you revise these concepts and strengthen your Biology preparation.

Definition And Scope Of Biomolecules

Bio means related to life, while molecules are substances formed by the combination of atoms. Biomolecules are organic compounds that form the bodies of living organisms and participate in life processes.

Six elements account for more than 98% of the body weight of living organisms:

• C: Carbon

• H: Hydrogen

• O: Oxygen

• N: Nitrogen

• S: Sulfur

• P: Phosphorus

Water forms approximately 70% of the body. Proteins, carbohydrates, lipids, and nucleic acids also contain these major elements.

Elemental, Chemical, And Ash Analysis

Elemental Analysis

Elemental analysis identifies the elements present in a sample and determines their relative proportions. Living and non-living matter contain many of the same elements, but their percentage compositions differ.

For example, silicon is abundant in the Earth's crust but is not a major constituent of the human body. Carbon, hydrogen, nitrogen, sulfur, and phosphorus are important components of living matter.

The key concept is that the elements may be similar, but their relative abundance differs between living and non-living matter.

Chemical Analysis

Chemical analysis helps identify the compounds present in biological material. In a commonly described procedure, a tissue sample is ground in trichloroacetic acid and filtered.

• Filtrate: The liquid that passes through the filter.

• Retentate: The material retained by the filter.

The filtrate contains the acid-soluble pool, which includes many small molecules, such as amino acids, monosaccharides, nucleotides, and inorganic ions.

The retentate contains the acid-insoluble fraction, which includes proteins, nucleic acids, polysaccharides, and lipids. Lipids are included largely because they are insoluble in water and remain associated with the insoluble fraction, even though many lipid molecules are relatively small.

Spectroscopic Analysis

Spectroscopic methods measure how substances interact with electromagnetic radiation. Depending on the technique, these methods can help identify functional groups, estimate concentrations, and investigate molecular structure. Molecular mass can be determined using suitable analytical techniques, such as mass spectrometry.

Ash Analysis

In ash analysis, a biological sample is heated strongly so that water and most organic matter are removed. The remaining ash contains inorganic mineral components.

This method helps investigate the inorganic constituents of biological material, including mineral elements and their compounds.

Biomicro And Biomacromolecules

Biological compounds can be grouped according to their size and chemical characteristics.

Biomicromolecules are relatively small molecules. Examples include amino acids, monosaccharides, nucleotides, and inorganic ions.

Biomacromolecules are larger biological molecules, commonly including proteins, nucleic acids, and polysaccharides. Many have molecular masses above 1,000 daltons.

Primary And Secondary Metabolites

A metabolite is a molecule involved in metabolism. Primary metabolites directly support growth, development, reproduction, survival, respiration, and energy production. Examples include glucose and amino acids.

Secondary metabolites are produced from primary metabolites but do not directly participate in metabolic reactions. Examples include:

• Alkaloids: Morphine and codeine

• Pigments: Carotenoids and anthocyanins

• Toxins: Abrin and ricin

• Drugs: Vinblastine

• Polymeric substances: Rubber, gum, and cellulose

• Essential oils: Lemongrass oil

• Lectins: Concanavalin A

Anthocyanins are water-soluble pigments found in vacuoles. Carotenoids are generally lipid-soluble and associated with membranes.

Amino Acids And Proteins

Amino Acids

Amino acids are the building blocks of proteins. A typical amino acid contains an amino group, a carboxyl group, a hydrogen atom, and a variable R group attached to the alpha carbon.

The R group determines many of an amino acid's chemical properties.

• Glycine: Has hydrogen as its R group and is the simplest amino acid.

• Alanine: Has a methyl group as its R group.

• Serine: Has a hydroxymethyl group as its R group.

Memory Tip: GAS represents Glycine, Alanine, and Serine.

Amino acids can be classified according to the properties of their side chains. Examples include:

• Aromatic: Phenylalanine, tyrosine, and tryptophan.

• Acidic: Aspartic acid and glutamic acid.

• Basic: Lysine, arginine, and histidine.

• Sulfur-containing: Cysteine and methionine.

• Hydroxyl-containing: Serine, threonine, and tyrosine.

Zwitterions and Amino Acid Charge

Amino acids can carry different net charges depending on the pH of their surroundings.

• Low pH: Amino acids generally have a net positive charge.

• Near the isoelectric point: Many amino acids exist predominantly as zwitterions, carrying both positive and negative charges but having zero net charge.

• High pH: Amino acids generally have a net negative charge.

The isoelectric point is the pH at which an amino acid has no net electrical charge.

Peptide Bonds and Protein Formation

Amino acids join through peptide bonds to form polypeptide chains. A peptide bond forms between the carboxyl group of one amino acid and the amino group of another, with the release of a water molecule in the condensation reaction.

A polypeptide has two ends:

• N-terminal: The end with the free amino group.

• C-terminal: The end with the free carboxyl group.

A protein's amino acid sequence and three-dimensional structure determine its properties and biological function.

Carbohydrates

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones containing at least one chiral carbon. Glucose is a polyhydroxy aldehyde, while fructose is a polyhydroxy ketone. Both have the formula C6H12O6 and are isomers.

Carbohydrates are classified by the number of sugar units:

• Monosaccharide: One unit

• Disaccharide: Two units

• Oligosaccharide: A few units

• Polysaccharide: Ten or more units

Examples:

• Sucrose gives glucose and fructose.

• Maltose gives two glucose molecules.

• Lactose gives glucose and galactose.

Important Polysaccharides

Starch consists of two major components:

• Amylose: A largely unbranched chain of glucose units.

• Amylopectin: A branched glucose polymer.

Glycogen is also branched and has frequent branching points. In starch and glycogen, the main chains primarily contain alpha-1,4 glycosidic bonds, while branching points contain alpha-1,6 glycosidic bonds.

Cellulose contains beta-1,4 glycosidic bonds, which produce straight chains suited to structural support.

Reducing and Non-Reducing Sugars

Reducing sugars have a free anomeric carbon or can form a structure capable of reducing suitable reagents. Glucose, lactose, and maltose are reducing sugars, whereas sucrose is a non-reducing sugar because both anomeric carbons participate in its glycosidic bond.

The terms reducing end and non-reducing end are also used when describing polysaccharide chains. These terms depend on the chemical structure at each end, not simply on its position on a page.

Iodine Test and Glucose Linkages

Starch produces a blue-black colour with iodine, largely because iodine interacts with the helical structure of amylose. Cellulose does not produce the same characteristic blue-black reaction.

Alpha-glucose forms the main chains of starch and glycogen, whereas beta-glucose forms cellulose. RNA contains the five-carbon sugar ribose, while DNA contains deoxyribose

Lipids

A fatty acid contains a carboxyl group attached to a hydrocarbon chain.

• Palmitic acid: A saturated fatty acid containing 16 carbon atoms.

• Arachidonic acid: An unsaturated fatty acid containing 20 carbon atoms and four double bonds.

Glycerol is a three-carbon alcohol with three hydroxyl groups. Fatty acids can combine with glycerol through ester bonds.

• One fatty acid attached to glycerol forms a monoacylglycerol.

• Two fatty acids form a diacylglycerol.

• Three fatty acids form a triacylglycerol.

Nucleic Acids And ATP

Nucleic acids are polymers of nucleotides that store, transmit, and help express genetic information. The two main types are DNA and RNA.

Nucleotides and Nitrogenous Bases

A nucleotide contains three components:

1. A nitrogenous base.

2. A pentose sugar.

3. One or more phosphate groups.

Nitrogenous bases are divided into two groups:

• Purines: Adenine and guanine. These have two fused rings.

• Pyrimidines: Cytosine, thymine, and uracil. These have one ring.

Memory Tip: A and G are purines. The remaining bases—C, U, and T—are pyrimidines.

DNA contains adenine, thymine, guanine, and cytosine. RNA contains adenine, uracil, guanine, and cytosine.

DNA contains deoxyribose, while RNA contains ribose.

Nucleoside and Nucleotide

A nucleoside consists of a nitrogenous base attached to a pentose sugar. Adding one or more phosphate groups produces a nucleotide.

• The base attaches to the sugar through an N-glycosidic bond.

• A phosphate group can attach to the sugar through a phosphoester bond.

• Nucleotides in nucleic acid chains are linked through 3′–5′ phosphodiester bonds.

These distinctions are useful for questions on nucleotide structure and DNA or RNA formation.

ATP: Energy Currency of the Cell

Adenosine triphosphate (ATP) consists of adenine, ribose, and three phosphate groups. Adenine and ribose together form adenosine.

ATP transfers usable chemical energy to many cellular processes, including active transport, muscle contraction, and biosynthesis. It is commonly called the energy currency of the cell because cells use ATP to couple energy-releasing reactions with energy-requiring activities.

Metabolism and Enzymes

Metabolism

Metabolism refers to the total set of chemical reactions occurring in a living organism or cell.

It includes two broad categories:

• Catabolism: Breaks down complex molecules into simpler substances and often releases usable energy.

• Anabolism: Builds complex molecules from simpler substances and generally requires energy.

For example, the breakdown of glucose during cellular respiration is catabolic, while the synthesis of proteins from amino acids is anabolic.

Enzymes as Biological Catalysts

Enzymes are biological catalysts that increase reaction rates by lowering the activation energy required for a reaction. Most enzymes are proteins, although some RNA molecules, called ribozymes, also have catalytic activity.

The substrate binds to an enzyme's active site, forming an enzyme-substrate complex. The reaction proceeds, products are released, and the enzyme can catalyse another reaction.

A simplified representation is: E + S ⇌ ES → E + P

Here, E represents the enzyme, S the substrate, ES the enzyme-substrate complex, and P the product.

Factors Affecting Enzyme Activity

Enzyme activity depends on several conditions.

• Temperature: Activity generally increases with temperature up to an optimum. Excessive heat can disrupt the enzyme's structure and reduce activity.

• pH: Each enzyme has a suitable pH range. Conditions far from the optimum can alter the active site or enzyme structure.

• Substrate concentration: Increasing substrate concentration generally increases reaction rate until the enzyme approaches saturation.

• Enzyme concentration: When enough substrate is available, increasing enzyme concentration can increase the reaction rate.

• Inhibitors: Certain molecules reduce enzyme activity by binding to the enzyme or affecting its function.

Many human enzymes function effectively near normal body temperature, approximately 37°C, but their individual optimum temperatures and pH values differ.

Enzyme Classification

Enzymes are classified according to the types of reactions they catalyse. The six major classes commonly taught in introductory biology are:

Memory Tip: O-T-H-L-I-L represents Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, and Ligases.

Enzyme Inhibition

Enzyme inhibitors reduce or prevent enzyme activity. Their effects depend on how they interact with the enzyme and the enzyme-substrate complex.

Competitive Inhibition

A competitive inhibitor competes with the substrate for the enzyme's active site. A commonly taught example is malonate, which competitively inhibits succinate dehydrogenase because it resembles succinate.

In the standard Michaelis-Menten model, competitive inhibition increases the apparent Km, while Vmax remains unchanged because sufficiently high substrate concentration can overcome the inhibition.

Non-Competitive Inhibition

In pure non-competitive inhibition, an inhibitor binds at a site distinct from the substrate-binding site and reduces catalytic activity. In the standard model, Vmax decreases while Km remains unchanged.

Not every inhibitor that binds away from the active site is purely non-competitive; mixed inhibition can affect both Km and Vmax.

Enzyme Cofactors

Some enzymes require non-protein components called cofactors to function properly.

• Apoenzyme: The protein component of an enzyme without its required cofactor.

• Cofactor: A non-protein component needed for enzyme activity.

• Holoenzyme: The active enzyme complex consisting of the apoenzyme and its required cofactor.

Cofactors are commonly grouped into three types:

Many coenzymes are derived from vitamins. NAD⁺ and NADP⁺ participate in electron-transfer reactions, while metal ions can help stabilise enzyme structures or participate directly in catalysis.

Biomolecules form the chemical foundation of life, making their structures, functions and interactions important topics for NEET Biology. Focus on distinguishing biomacromolecules from micromolecules, understanding proteins, carbohydrates and nucleic acids, and revising metabolism, enzyme inhibition and cofactors. PW supports this preparation through Biology classes, study materials, practice questions and mock tests, helping aspirants revise key concepts and assess their understanding.