Biomolecules – Class 11 Biology Notes
Introduction to Biomolecules
Biomolecules are organic molecules that are essential for life. They are involved in almost every process that occurs in living organisms, such as energy production, cellular structure, and regulation of metabolism. Biomolecules include carbohydrates, proteins, lipids, and nucleic acids. These molecules are the building blocks of life and can be classified as macromolecules (large molecules) and micromolecules (small molecules).
1. Carbohydrates
Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. They are the primary source of energy for living organisms and are found in foods like grains, fruits, and vegetables.
Structure of Carbohydrates:
- Monosaccharides: Simple sugars that cannot be broken down into simpler sugars.
- Examples: Glucose, fructose, galactose.
- Disaccharides: Formed by the combination of two monosaccharides via a glycosidic bond.
- Examples: Sucrose (glucose + fructose), lactose (glucose + galactose).
- Polysaccharides: Complex carbohydrates made up of many monosaccharides.
- Examples: Starch, glycogen, cellulose.
Functions of Carbohydrates:
- Energy Source: Carbohydrates like glucose are broken down during cellular respiration to provide energy (ATP).
- Storage: Starch (in plants) and glycogen (in animals) serve as energy storage.
- Structural Role: Cellulose provides structural support in plant cell walls.
2. Proteins
Proteins are large, complex molecules made up of amino acids. They play a vital role in almost all cellular processes, including catalyzing reactions, providing structure, and supporting immune function.
Structure of Proteins:
- Amino Acids: The building blocks of proteins, each consisting of an amino group, a carboxyl group, and a unique side chain (R group).
- Peptide Bond: The bond formed between the amino group of one amino acid and the carboxyl group of another.
- Levels of Protein Structure:
- Primary Structure: The linear sequence of amino acids.
- Secondary Structure: The folding of the polypeptide chain into alpha-helices or beta-pleated sheets.
- Tertiary Structure: The three-dimensional shape of the protein.
- Quaternary Structure: The interaction of multiple polypeptide chains to form a functional protein.
Functions of Proteins:
- Enzymes: Catalyze biochemical reactions (e.g., amylase, lipase).
- Structural Proteins: Provide support and shape to cells (e.g., collagen, keratin).
- Transport Proteins: Help transport molecules (e.g., hemoglobin).
- Defensive Proteins: Involved in immune response (e.g., antibodies).
3. Lipids
Lipids are a diverse group of hydrophobic molecules, including fats, oils, and phospholipids. They are primarily composed of carbon, hydrogen, and oxygen, and some contain phosphorus.
Structure of Lipids:
- Fatty Acids: Long hydrocarbon chains with a carboxyl group at one end.
- Triglycerides: Consist of three fatty acids linked to a glycerol molecule.
- Phospholipids: Consist of two fatty acids, a glycerol molecule, and a phosphate group. They form the structural component of cell membranes.
- Steroids: Lipids with a carbon skeleton consisting of four fused rings (e.g., cholesterol).
Functions of Lipids:
- Energy Storage: Triglycerides store energy in adipose tissue.
- Insulation: Lipids help insulate the body and organs, preventing heat loss.
- Cell Membrane Structure: Phospholipids are a major component of the cell membrane.
- Hormonal Function: Steroids like hormones (e.g., estrogen, testosterone) regulate various physiological processes.
4. Nucleic Acids
Nucleic acids are polymers of nucleotides and are responsible for the storage, transmission, and expression of genetic information. The two types of nucleic acids are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
Structure of Nucleic Acids:
- Nucleotides: The building blocks of nucleic acids, each consisting of a sugar molecule, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, guanine, or uracil).
- DNA Structure: Double-stranded helix, with adenine (A) pairing with thymine (T), and cytosine (C) pairing with guanine (G).
- RNA Structure: Single-stranded, with adenine pairing with uracil (U), and cytosine pairing with guanine.
Functions of Nucleic Acids:
- DNA: Stores genetic information and is involved in heredity.
- RNA: Helps in protein synthesis and gene expression.
- ATP (Adenosine Triphosphate): A nucleotide that serves as the primary energy carrier in cells.
5. Enzymes
Enzymes are proteins that act as biological catalysts to speed up chemical reactions in the body. They are highly specific to the substrates they act upon and work by lowering the activation energy required for a reaction to occur.
Enzyme Action:
- Active Site: The region of the enzyme where the substrate binds.
- Lock and Key Model: The substrate fits perfectly into the enzyme’s active site.
- Induced Fit Model: The enzyme undergoes a conformational change when the substrate binds.
Factors Affecting Enzyme Activity:
- Temperature: Enzyme activity increases with temperature until it reaches an optimal point, beyond which it denatures.
- pH: Each enzyme has an optimal pH range for activity.
- Substrate Concentration: Increasing substrate concentration increases enzyme activity until the enzyme becomes saturated.
MCQs – Biomolecules
1. Which of the following is the primary function of carbohydrates in living organisms?
a) Energy storage
b) Genetic information storage
c) Catalyzing biochemical reactions
d) Protection against pathogens
Answer: a) Energy storage
2. Which of the following is a protein involved in the immune response?
a) Hemoglobin
b) Insulin
c) Antibodies
d) Collagen
Answer: c) Antibodies
3. Which of the following is NOT a function of lipids?
a) Energy storage
b) Structural component of membranes
c) Storage of genetic information
d) Insulation and protection
Answer: c) Storage of genetic information
4. Which type of RNA carries genetic information from DNA to the ribosome for protein synthesis?
a) mRNA
b) tRNA
c) rRNA
d) snRNA
Answer: a) mRNA
5. The primary function of enzymes is to:
a) Carry genetic information
b) Speed up chemical reactions
c) Provide energy
d) Act as structural components of cells
Answer: b) Speed up chemical reactions
6. The building blocks of proteins are:
a) Nucleotides
b) Fatty acids
c) Amino acids
d) Simple sugars
Answer: c) Amino acids
7. Which of the following is a function of nucleic acids?
a) Store and transmit genetic information
b) Provide structural support to cells
c) Catalyze biochemical reactions
d) Serve as energy carriers
Answer: a) Store and transmit genetic information
8. Which of the following is a characteristic of triglycerides?
a) They are composed of two fatty acids and a glycerol molecule
b) They are found in plant cells only
c) They serve as a source of long-term energy storage
d) They are involved in cell signaling
Answer: c) They serve as a source of long-term energy storage
9. The process by which a protein’s three-dimensional structure is altered is called:
a) Hydrolysis
b) Denaturation
c) Condensation
d) Synthesis
Answer: b) Denaturation
10. Which of the following is a carbohydrate that provides structural support in plant cell walls?
a) Glycogen
b) Starch
c) Cellulose
d) Chitin
Answer: c) Cellulose