JEE Chemistry Notes: Biomolecules

Introduction to Biomolecules

Biomolecules are molecules that are involved in the structure and function of living organisms. They play vital roles in various biochemical processes that sustain life. Biomolecules are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. They are categorized into four main groups: carbohydrates, proteins, lipids, and nucleic acids. Understanding the structure, properties, and functions of these biomolecules is essential for JEE Chemistry.

Carbohydrates

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen atoms, and they serve as the primary source of energy for living organisms. They are classified into three main types based on their structure:

• Monosaccharides: These are the simplest form of carbohydrates and cannot be hydrolyzed into simpler sugars. Common examples include glucose (C₆H₁₂O₆), fructose, and galactose.

• Disaccharides: Disaccharides consist of two monosaccharide units joined by a glycosidic bond. Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

• Polysaccharides: These are complex carbohydrates made up of long chains of monosaccharide units. Examples include starch, cellulose, and glycogen.

Functions of Carbohydrates:

• Energy Source: Carbohydrates are the primary source of energy for living organisms. Glucose, for example, is broken down during cellular respiration to release energy.

• Structural Role: Polysaccharides like cellulose provide structural support in plants, while glycogen serves as energy storage in animals.

Properties of Carbohydrates:

• Solubility: Simple carbohydrates like monosaccharides and disaccharides are soluble in water, whereas polysaccharides are generally insoluble.

• Reducing and Non-Reducing Sugars: Monosaccharides and disaccharides like maltose and lactose are reducing sugars, while sucrose is a non-reducing sugar due to its lack of a free aldehyde or ketone group.

Proteins

Proteins are large, complex biomolecules made up of amino acids. They are the building blocks of living organisms and play various roles in biological functions, including catalysis, structural support, and immune defense.

• Structure of Proteins: The structure of proteins is classified into four levels:

  • Primary Structure: The sequence of amino acids linked by peptide bonds.

  • Secondary Structure: Local folding of the polypeptide chain into structures like alpha helices and beta sheets, stabilized by hydrogen bonds.

  • Tertiary Structure: The overall 3D shape of the protein formed by interactions between the side chains (R groups) of amino acids.

  • Quaternary Structure: The arrangement of multiple polypeptide chains into a functional protein complex.

Functions of Proteins:

• Enzymatic Activity: Proteins serve as enzymes that catalyze biochemical reactions, such as the digestion of food and the synthesis of DNA.

• Structural Support: Proteins like collagen provide structural integrity to tissues, while keratin is a structural protein found in hair and skin.

• Transport and Storage: Hemoglobin is a protein that transports oxygen in the blood, while myoglobin stores oxygen in muscles.

• Immunological Functions: Antibodies are proteins involved in the immune response, protecting the body from pathogens.

Properties of Proteins:

• Denaturation: Proteins lose their functional shape (tertiary and quaternary structures) due to factors like heat, pH changes, or chemicals, leading to denaturation.

• Solubility: Many proteins are soluble in water, particularly those with polar amino acid side chains.

Lipids

Lipids are hydrophobic or amphiphilic compounds made up mainly of carbon, hydrogen, and oxygen. They play essential roles in energy storage, membrane structure, and signaling.

• Types of Lipids:

  • Fats and Oils: These are triglycerides made from glycerol and fatty acids. Fats are solid at room temperature, while oils are liquid.

  • Phospholipids: These are major components of biological membranes, composed of glycerol, two fatty acids, and a phosphate group.

  • Steroids: These are lipids with a characteristic ring structure, including hormones like testosterone and cholesterol.

Functions of Lipids:

• Energy Storage: Lipids are a concentrated source of energy, providing more energy per gram than carbohydrates or proteins.

• Cell Membrane Structure: Phospholipids are essential components of cell membranes, forming bilayers that provide structural integrity.

• Signaling Molecules: Steroid hormones, such as estrogen and testosterone, regulate physiological processes.

Properties of Lipids:

• Hydrophobicity: Lipids are generally insoluble in water due to their nonpolar nature, but they are soluble in organic solvents like alcohol and ether.

Nucleic Acids

Nucleic acids are biomolecules that store and transfer genetic information in cells. They are composed of nucleotides, which are the building blocks of DNA and RNA.

• DNA (Deoxyribonucleic Acid): DNA is the genetic material that carries the instructions for the growth, development, and functioning of all living organisms. It is a double-stranded molecule with a helical structure.

• RNA (Ribonucleic Acid): RNA plays a key role in protein synthesis and gene expression. Unlike DNA, RNA is single-stranded.

• Structure of Nucleic Acids: Both DNA and RNA are made of long chains of nucleotides, each consisting of a phosphate group, a sugar (deoxyribose in DNA and ribose in RNA), and a nitrogenous base (adenine, thymine, cytosine, and guanine in DNA; uracil replaces thymine in RNA).

Functions of Nucleic Acids:

• Genetic Information Storage: DNA stores genetic information in cells, which is passed from one generation to the next during reproduction.

• Protein Synthesis: RNA helps in translating genetic information from DNA into proteins by directing the synthesis of proteins in the ribosomes.

Properties of Nucleic Acids:

• Base Pairing: In DNA, adenine pairs with thymine, and cytosine pairs with guanine, forming the double-stranded structure.

• Stability: DNA is more stable than RNA due to the lack of a hydroxyl group at the 2' position in its sugar (deoxyribose).

Enzymes and Coenzymes

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are typically proteins, though some RNA molecules (ribozymes) can also act as enzymes.

• Mechanism of Action: Enzymes lower the activation energy of a reaction, allowing it to proceed more quickly.

• Coenzymes: Coenzymes are small molecules that assist enzymes in their catalytic activity. They often carry functional groups between different enzyme reactions. Examples include vitamins like B₆ and B₁₂.

Vitamins and Minerals

Vitamins are organic compounds that are essential for normal metabolism but are required in small amounts. They can be fat-soluble (A, D, E, K) or water-soluble (B-complex, C). Minerals like calcium, potassium, and iron are inorganic elements required in various biochemical processes.

Applications of Biomolecules in Medicine

• Medicinal Use of Proteins: Insulin, a protein hormone, is used to manage diabetes. Monoclonal antibodies are used in cancer treatment.

• Biotechnology: Recombinant DNA technology allows for the production of biomolecules like human insulin, growth hormones, and vaccines.

JEE Specific Practice Problems

• Identifying the functional group present in biomolecules like carbohydrates, proteins, and lipids.

• Writing the structural formula for different carbohydrates, amino acids, and nucleotides.

• Solving problems related to the biological functions of biomolecules.

Mastering the concepts of biomolecules and their applications will help you understand key biochemical processes and aid in solving questions related to biochemistry in the JEE examination.