Biomolecules: Comprehensive NEET Chemistry Notes

1. Introduction to Biomolecules

Biomolecules are organic compounds that are vital for the growth, sustenance, and reproduction of living organisms. They include carbohydrates, proteins, nucleic acids, and lipids, all of which play crucial roles in the biochemical processes that sustain life. This chapter will cover the structure, classification, and functions of these biomolecules, providing a foundational understanding for NEET aspirants.

2. Carbohydrates

2.1 Definition and Classification

Carbohydrates are optically active polyhydroxy aldehydes or ketones or compounds that yield such structures upon hydrolysis. They are broadly classified into three groups:

  1. Monosaccharides: Simplest form that cannot be hydrolyzed further (e.g., glucose, fructose).
  2. Oligosaccharides: Yield two to ten monosaccharide units upon hydrolysis (e.g., sucrose, maltose).
  3. Polysaccharides: Yield a large number of monosaccharide units upon hydrolysis (e.g., starch, cellulose).

Did You Know?

Glucose, a monosaccharide, is the most abundant organic compound on Earth.

2.2 Monosaccharides

Monosaccharides are further classified based on the number of carbon atoms and the functional group present:

  • Aldoses: Contain an aldehyde group (e.g., glucose).
  • Ketoses: Contain a keto group (e.g., fructose).

2.3 Disaccharides and Polysaccharides

  • Disaccharides: Formed by two monosaccharides linked by a glycosidic bond (e.g., sucrose).
  • Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds (e.g., starch, glycogen).

Common Misconception:

Not all compounds fitting the general formula Cx(H2O)y are carbohydrates. For example, acetic acid fits this formula but is not a carbohydrate.

NEET Tip:

Remember the structure and function of key polysaccharides like starch and cellulose, as they are frequently tested in NEET.

3. Proteins

3.1 Structure and Classification

Proteins are polymers of amino acids linked by peptide bonds. They are classified based on their shape and structure:

  • Fibrous Proteins: Long, insoluble, and provide structural support (e.g., keratin, collagen).
  • Globular Proteins: Spherical, soluble, and perform various functions (e.g., enzymes, hemoglobin).

3.2 Levels of Protein Structure

Proteins have four levels of structure:

  1. Primary Structure: Sequence of amino acids.
  2. Secondary Structure: Local folding into alpha-helices or beta-sheets.
  3. Tertiary Structure: Overall 3D shape formed by further folding.
  4. Quaternary Structure: Association of multiple polypeptide chains.

Mnemonic:

"Proteins Have Several Structural Levels" (Primary, Helices/Sheets, Tertiary, Quaternary)

3.3 Denaturation

Denaturation involves the loss of protein structure and function due to changes in pH, temperature, or chemical exposure. This process disrupts secondary and tertiary structures but leaves the primary structure intact.

Real-life Application:

The coagulation of egg whites when boiled is a common example of protein denaturation.

4. Enzymes

4.1 Role and Function

Enzymes are biological catalysts that speed up biochemical reactions without being consumed. They are highly specific, acting only on specific substrates.

4.2 Mechanism of Action

Enzymes lower the activation energy required for reactions. They bind substrates at their active sites, forming enzyme-substrate complexes that facilitate the reaction.

NEET Tip:

Understand the factors affecting enzyme activity, such as temperature, pH, and substrate concentration, as these concepts are crucial for NEET.

5. Nucleic Acids

5.1 Structure and Types

Nucleic acids are polymers of nucleotides, each consisting of a sugar, a phosphate group, and a nitrogenous base. They are classified into two types:

  • DNA (Deoxyribonucleic Acid): Contains deoxyribose sugar and bases adenine (A), guanine (G), cytosine (C), and thymine (T). DNA is double-stranded and carries genetic information.
  • RNA (Ribonucleic Acid): Contains ribose sugar and bases adenine (A), guanine (G), cytosine (C), and uracil (U). RNA is single-stranded and involved in protein synthesis.

5.2 Functions

  • DNA: Stores genetic information and directs protein synthesis.
  • RNA: Transfers genetic information from DNA to ribosomes for protein synthesis.

Did You Know?

The double-helix structure of DNA was discovered by James Watson and Francis Crick, earning them the Nobel Prize in 1962.

6. Vitamins

6.1 Definition and Classification

Vitamins are organic compounds required in small amounts for normal growth and health. They are classified based on their solubility:

  • Fat-Soluble Vitamins: Vitamins A, D, E, and K. Stored in the body's fat tissues.
  • Water-Soluble Vitamins: Vitamins B and C. Not stored in the body and must be consumed regularly.

6.2 Functions and Sources

  • Vitamin A: Essential for vision and immune function. Sources: Carrots, fish liver oil.
  • Vitamin C: Important for collagen synthesis and antioxidant activity. Sources: Citrus fruits, green vegetables.
  • Vitamin D: Regulates calcium and phosphate metabolism. Sources: Sunlight, fish.

Common Misconception:

Taking excess vitamins can be harmful. Vitamin supplements should be taken only under medical advice.

Quick Recap

  • Carbohydrates: Classified into monosaccharides, disaccharides, and polysaccharides. Essential for energy storage and structural functions.
  • Proteins: Polymers of amino acids with primary, secondary, tertiary, and quaternary structures. Functions include structural support, catalysis, and transport.
  • Enzymes: Biological catalysts that speed up reactions by lowering activation energy.
  • Nucleic Acids: DNA and RNA, responsible for storing and transferring genetic information.
  • Vitamins: Essential nutrients classified as fat-soluble or water-soluble, required for various biochemical functions.

Practice Questions

Question 1

Describe the primary structure of proteins. Answer: The primary structure of proteins refers to the linear sequence of amino acids linked by peptide bonds in a polypeptide chain.

Question 2

Explain the difference between DNA and RNA. Answer: DNA is a double-stranded molecule with deoxyribose sugar and bases adenine, guanine, cytosine, and thymine. RNA is a single-stranded molecule with ribose sugar and bases adenine, guanine, cytosine, and uracil.

Question 3

What is denaturation of proteins? Provide an example. Answer: Denaturation is the process where a protein loses its native structure and function due to external factors like pH or temperature changes. An example is the coagulation of egg whites upon boiling.

Question 4

List three functions of carbohydrates in living organisms. Answer:

  1. Energy storage (e.g., glycogen in animals, starch in plants).
  2. Structural components (e.g., cellulose in plant cell walls).
  3. Components of nucleic acids (e.g., ribose in RNA).

Question 5

What are the fat-soluble vitamins, and why are they important? Answer: Fat-soluble vitamins include A, D, E, and K. They are important for vision, bone health, antioxidant protection, and blood clotting, respectively.

Did You Know?

Vitamin D is often called the "sunshine vitamin" because the body can synthesize it upon exposure to sunlight.