Biomolecules Notes

Introduction

Biomolecules are organic molecules that are essential to life. They include carbohydrates, proteins, lipids, and nucleic acids. Understanding the structure, function, and interactions of these molecules is crucial for mastering JEE Advanced Chemistry. This study note will break down each type of biomolecule, their properties, and their roles in biological systems.

Carbohydrates

Structure and Classification

Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. They are classified into three main groups:

1. Monosaccharides: The simplest form of carbohydrates, consisting of a single sugar unit. Examples include glucose and fructose.
2. Disaccharides: Formed by the combination of two monosaccharide units. Examples include sucrose and lactose.
3. Polysaccharides: Long chains of monosaccharide units. Examples include starch, cellulose, and glycogen.

Monosaccharides

Monosaccharides can be classified based on the number of carbon atoms they contain:

• Trioses: 3 carbon atoms (e.g., glyceraldehyde)
• Tetroses: 4 carbon atoms (e.g., erythrose)
• Pentoses: 5 carbon atoms (e.g., ribose)
• Hexoses: 6 carbon atoms (e.g., glucose, fructose)

Structure of Glucose

Glucose is an aldohexose with the molecular formula $C_6H_{12}O_6$. It exists in a cyclic form in aqueous solutions due to the intramolecular reaction between the aldehyde group and a hydroxyl group.

$$ \text{Glucose: } \text{Cyclic structure} $$

Figure: Structure of Glucose

Disaccharides

Disaccharides are formed by a glycosidic bond between two monosaccharides. For example:

• Sucrose: Glucose + Fructose
• Lactose: Glucose + Galactose
• Maltose: Glucose + Glucose

Polysaccharides

Polysaccharides are complex carbohydrates. They serve as energy storage (e.g., starch in plants, glycogen in animals) and structural components (e.g., cellulose in plant cell walls).

Proteins

Structure and Classification

Proteins are polymers of amino acids linked by peptide bonds. They play crucial roles in biological processes, including catalysis (enzymes), transport (hemoglobin), and structural support (collagen).

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid has a central carbon atom (alpha carbon) bonded to:

• An amino group ($-NH_2$)
• A carboxyl group ($-COOH$)
• A hydrogen atom
• A variable R group (side chain)

Levels of Protein Structure

1. Primary Structure: The sequence of amino acids in a polypeptide chain.
2. Secondary Structure: Local folding patterns of the polypeptide chain, such as alpha helices and beta sheets, stabilized by hydrogen bonds.
3. Tertiary Structure: The overall three-dimensional shape of a single polypeptide chain, stabilized by various interactions including hydrogen bonds, disulfide bridges, and hydrophobic interactions.
4. Quaternary Structure: The arrangement of multiple polypeptide chains into a functional protein complex.

Lipids

Structure and Classification

Lipids are a diverse group of hydrophobic molecules, including fats, oils, phospholipids, and steroids. They are primarily composed of carbon, hydrogen, and oxygen.

Types of Lipids

1. Triglycerides: Composed of glycerol and three fatty acids. They are the main form of stored energy in animals.
2. Phospholipids: Major components of cell membranes, consisting of two fatty acids, a glycerol molecule, and a phosphate group.
3. Steroids: Lipids with a characteristic four-ring structure. Cholesterol is a common example.

Functions of Lipids

• Energy storage
• Structural components of cell membranes
• Signaling molecules (e.g., hormones)

Nucleic Acids

Structure and Types

Nucleic acids are polymers of nucleotides, which consist of a nitrogenous base, a sugar, and a phosphate group. There are two main types:

1. DNA (Deoxyribonucleic Acid): Contains the genetic blueprint for life. It is composed of two strands forming a double helix.
2. RNA (Ribonucleic Acid): Involved in protein synthesis and gene regulation. It is usually single-stranded.

DNA Structure

DNA is composed of four types of nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The bases pair specifically (A with T, C with G) through hydrogen bonds.

$$ \text{DNA: Double helix structure} $$

Figure: Double Helix Structure of DNA

RNA Structure

RNA has a similar structure to DNA but with uracil (U) instead of thymine (T), and it is usually single-stranded.

Conclusion

Understanding biomolecules is fundamental for mastering JEE Advanced Chemistry. This includes recognizing their structures, functions, and interactions. Carbohydrates, proteins, lipids, and nucleic acids each play unique and vital roles in biological systems. By breaking down these complex topics into digestible sections, you can better grasp their importance and applications.