Biomolecules Notes

Introduction

Biomolecules are organic molecules that are essential for life. These molecules include carbohydrates, proteins, lipids, and nucleic acids. Understanding biomolecules is crucial for JEE Main Chemistry as they form the basis of various biochemical processes and reactions. This study note will break down the complex ideas into smaller sections to make them easily digestible.

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically with a hydrogen:oxygen atom ratio of 2:1. They are classified based on the number of sugar units they contain.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and cannot be hydrolyzed into smaller units. They are classified based on the number of carbon atoms:

• Triose (3 carbons): Glyceraldehyde
• Tetrose (4 carbons): Erythrose
• Pentose (5 carbons): Ribose
• Hexose (6 carbons): Glucose, Fructose

Disaccharides

Disaccharides are composed of two monosaccharide units linked by a glycosidic bond. Examples include:

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

Polysaccharides

Polysaccharides are long chains of monosaccharide units. They can be either storage polysaccharides or structural polysaccharides.

• Storage Polysaccharides: Starch (plants), Glycogen (animals)
• Structural Polysaccharides: Cellulose (plants), Chitin (fungi and insects)

Proteins

Proteins are large biomolecules consisting of one or more long chains of amino acid residues. They play various roles in the body, including catalyzing metabolic reactions, DNA replication, and transporting molecules.

Amino Acids

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

1. Hydrogen atom ($H$)
2. Carboxyl group ($-COOH$)
3. Amino group ($-NH_2$)
4. R-group (side chain)

Peptide Bond Formation

A peptide bond is formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water ($H_2O$):

$$ \text{Amino Acid}_1 - COOH + \text{Amino Acid}_2 - NH_2 \rightarrow \text{Amino Acid}_1 - CO - NH - \text{Amino Acid}_2 + H_2O $$

Protein Structure

Proteins have four levels of structure:

1. Primary Structure: Sequence of amino acids
2. Secondary Structure: Folding into α-helices and β-pleated sheets, stabilized by hydrogen bonds
3. Tertiary Structure: 3D folding due to interactions between R-groups
4. Quaternary Structure: Multiple polypeptide chains coming together

Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, oils, waxes, and steroids. They are composed mainly of carbon and hydrogen atoms and play key roles in energy storage, membrane structure, and signaling.

Fatty Acids

Fatty acids are long hydrocarbon chains with a carboxyl group at one end. They can be:

• Saturated: No double bonds (e.g., stearic acid)
• Unsaturated: One or more double bonds (e.g., oleic acid)

Triglycerides

Triglycerides are formed by esterification of three fatty acids with glycerol:

$$ \text{Glycerol} + 3 \text{Fatty Acids} \rightarrow \text{Triglyceride} + 3 H_2O $$

Phospholipids

Phospholipids consist of two fatty acids, a glycerol unit, and a phosphate group. They are major components of cell membranes, forming a bilayer.

Nucleic Acids

Nucleic acids are biopolymers essential for all known forms of life. They include DNA and RNA, which are composed of nucleotides.

Nucleotides

A nucleotide consists of three components:

1. Nitrogenous Base: Adenine (A), Thymine (T), Cytosine (C), Guanine (G) for DNA; Uracil (U) replaces Thymine in RNA
2. Pentose Sugar: Deoxyribose in DNA, Ribose in RNA
3. Phosphate Group

DNA Structure

DNA is a double helix formed by two polynucleotide chains held together by hydrogen bonds between complementary bases:

• A with T (2 hydrogen bonds)
• C with G (3 hydrogen bonds)

RNA Structure

RNA is usually single-stranded and plays various roles in protein synthesis and gene regulation.

Conclusion

Understanding the structure and function of biomolecules is essential for mastering JEE Main Chemistry. By breaking down complex ideas into smaller sections, we can better grasp the nuances of carbohydrates, proteins, lipids, and nucleic acids. Remember to focus on the key concepts and practice with examples to solidify your understanding.