Biomolecules are chemical compounds found in living organisms that play vital roles in sustaining life. They are responsible for building cell structures, storing and transmitting genetic information, catalyzing biochemical reactions, and providing energy. The study of biomolecules helps us understand the molecular basis of life processes.
In Class 12 Chemistry, the topic Biomolecules covers carbohydrates, proteins, enzymes, vitamins, nucleic acids, lipids, and hormones. These notes will help students understand the topic thoroughly and revise quickly for exams.
Class 12 Chemistry Notes – Biomolecules | Complete Explanation with Questions
Classification of Biomolecules
Biomolecules are broadly classified into four main types:
-
Carbohydrates
-
Proteins
-
Lipids
-
Nucleic Acids
Additionally, vitamins and hormones are also discussed as important biomolecules.
1. Carbohydrates
Definition
Carbohydrates are polyhydroxy aldehydes or ketones, or compounds that yield these on hydrolysis. They are commonly known as saccharides.
Functions of Carbohydrates
-
Provide energy to the body
-
Act as a reserve food material (e.g., glycogen in animals, starch in plants)
-
Serve structural roles (e.g., cellulose in plants)
Classification of Carbohydrates
a) Monosaccharides
-
Simplest carbohydrates
-
Cannot be hydrolyzed further
-
Examples: Glucose, Fructose, Galactose
b) Disaccharides
-
Composed of two monosaccharide units
-
Examples:
-
Sucrose = Glucose + Fructose (non-reducing)
-
Maltose = Glucose + Glucose (reducing)
-
Lactose = Glucose + Galactose (reducing)
-
c) Oligosaccharides
-
Contain 2–10 monosaccharide units
-
Less common in nature
d) Polysaccharides
-
Large molecules with several monosaccharide units
-
Examples: Starch, Glycogen, Cellulose
Reducing and Non-Reducing Sugars
-
Reducing sugars: Have a free aldehyde or ketone group (e.g., Glucose, Maltose)
-
Non-reducing sugars: Do not have free aldehyde or ketone group (e.g., Sucrose)
Important Reactions of Glucose
-
Oxidation: Glucose → Gluconic acid
-
Reduction: Glucose → Sorbitol
-
Reaction with phenylhydrazine: Formation of osazone crystals
-
Esterification: Formation of glucose pentaacetate
2. Proteins
Definition
Proteins are nitrogen-containing biomolecules formed by condensation of amino acids through peptide bonds.
Functions of Proteins
-
Structural components (keratin in hair, collagen in connective tissue)
-
Catalytic roles (enzymes)
-
Hormonal roles (insulin)
-
Defense roles (antibodies)
Amino Acids
-
Building blocks of proteins
-
Contain both amino group (-NH₂) and carboxyl group (-COOH)
-
Classified into:
-
Essential amino acids: Cannot be synthesized in the body
-
Non-essential amino acids: Synthesized in the body
-
Structure of Proteins
-
Primary structure: Sequence of amino acids
-
Secondary structure: α-Helix and β-Pleated sheet arrangement
-
Tertiary structure: 3D folding due to interactions among side chains
-
Quaternary structure: Multiple polypeptide chains linked together
Classification of Proteins
-
Fibrous proteins: Structural, water-insoluble (e.g., collagen, keratin)
-
Globular proteins: Functional, water-soluble (e.g., enzymes, hemoglobin)
3. Enzymes
Definition
Enzymes are biological catalysts that accelerate biochemical reactions without being consumed.
Characteristics
-
Highly specific in action
-
Work under mild temperature and pH
-
Show catalytic efficiency
Mechanism of Enzyme Action
-
Lock and Key Model: Substrate fits into the enzyme like a key fits into a lock.
-
Induced Fit Model: Enzyme changes shape to fit the substrate.
Factors Affecting Enzyme Activity
-
Temperature
-
pH
-
Substrate concentration
-
Inhibitors
4. Vitamins
Definition
Vitamins are essential organic compounds required in small amounts for normal growth and health.
Classification of Vitamins
-
Water-Soluble Vitamins: Vitamin B-complex, Vitamin C
-
Fat-Soluble Vitamins: Vitamin A, D, E, K
Deficiency Diseases
-
Vitamin A → Night blindness
-
Vitamin D → Rickets
-
Vitamin C → Scurvy
-
Vitamin K → Prolonged clotting time
5. Nucleic Acids
Definition
Nucleic acids are biomolecules responsible for storing and transmitting genetic information.
Types
-
DNA (Deoxyribonucleic acid)
-
RNA (Ribonucleic acid)
Structure of Nucleic Acids
-
Composed of nucleotides = Nitrogenous base + Sugar + Phosphate group
-
Nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T) in DNA, and Uracil (U) in RNA
Functions
-
DNA stores genetic information
-
RNA helps in protein synthesis
6. Lipids
Definition
Lipids are esters of fatty acids with alcohol, insoluble in water but soluble in organic solvents.
Types of Lipids
-
Simple lipids: Fats and oils
-
Compound lipids: Phospholipids, glycolipids
-
Derived lipids: Steroids, fatty acids
Functions of Lipids
-
Energy storage
-
Cell membrane formation
-
Hormone synthesis
7. Hormones (Brief Introduction)
Hormones are chemical messengers secreted by endocrine glands to regulate body functions.
Examples: Insulin, Thyroxine, Adrenaline
Importance of Biomolecules
-
Provide energy and structural support
-
Regulate biochemical reactions
-
Store and transfer genetic information
-
Maintain growth and development
Summary Table of Biomolecules
| Biomolecule | Monomer Unit | Examples | Functions |
|---|---|---|---|
| Carbohydrates | Monosaccharides | Glucose, Starch | Energy source, storage |
| Proteins | Amino acids | Enzymes, Hormones | Structural, catalytic roles |
| Nucleic acids | Nucleotides | DNA, RNA | Genetic information |
| Lipids | Fatty acids, Glycerol | Fats, Steroids | Energy storage, membranes |
Objective Questions-Class 12 Chemistry Notes – Biomolecules
Q1. What is the basic unit of proteins?
a) Glucose
b) Amino acid
c) Nucleotide
d) Fatty acid
Answer: The basic unit of proteins is amino acid.
Q2. Which biomolecule stores genetic information?
a) Protein
b) DNA
c) Lipid
d) Vitamin
Answer: Genetic information is stored in DNA.
Q3. Name the vitamin responsible for night blindness.
a) Vitamin B
b) Vitamin C
c) Vitamin A
d) Vitamin D
Answer: Night blindness is caused by a deficiency of Vitamin A.
Q4. Which sugar is known as grape sugar?
a) Fructose
b) Glucose
c) Lactose
d) Maltose
Answer: Glucose is commonly called grape sugar.
Q5. What is the monomer unit of nucleic acids?
a) Amino acid
b) Monosaccharide
c) Nucleotide
d) Fatty acid
Answer: The monomer unit of nucleic acids is nucleotide.
Q6. Name the hormone that controls blood sugar levels.
a) Thyroxine
b) Adrenaline
c) Insulin
d) Estrogen
Answer: Insulin controls the blood sugar level.
Q7. Which vitamin is also called ascorbic acid?
a) Vitamin C
b) Vitamin A
c) Vitamin D
d) Vitamin K
Answer: Vitamin C is also known as ascorbic acid.
Q8. Name the process of breakdown of glucose to produce energy.
a) Photosynthesis
b) Glycolysis
c) Respiration
d) Fermentation
Answer: Breakdown of glucose for energy is called Glycolysis.
Q9. Which type of protein forms hair and nails?
a) Collagen
b) Keratin
c) Myosin
d) Hemoglobin
Answer: Keratin forms hair and nails.
Q10. Which is the non-reducing sugar among the following?
a) Glucose
b) Sucrose
c) Maltose
d) Lactose
Answer: Sucrose is a non-reducing sugar.
Q11. Name the polysaccharide stored in the liver of animals.
a) Starch
b) Cellulose
c) Glycogen
d) Chitin
Answer: Glycogen is stored in the liver of animals.
Q12. Which type of RNA carries amino acids for protein synthesis?
a) mRNA
b) tRNA
c) rRNA
d) nRNA
Answer: tRNA (Transfer RNA) carries amino acids.
Q13. Name the vitamin responsible for blood clotting.
a) Vitamin C
b) Vitamin D
c) Vitamin A
d) Vitamin K
Answer: Vitamin K helps in blood clotting.
Q14. Which base is present in RNA but absent in DNA?
a) Adenine
b) Uracil
c) Thymine
d) Cytosine
Answer: Uracil is present in RNA but absent in DNA.
Q15. Name the enzyme that breaks down starch into maltose.
a) Maltase
b) Lipase
c) Amylase
d) Pepsin
Answer: Amylase breaks starch into maltose.
Q16. Which carbohydrate is the main component of plant cell walls?
a) Glycogen
b) Cellulose
c) Starch
d) Sucrose
Answer: Cellulose is the main component of plant cell walls.
Q17. Name the vitamin that prevents scurvy.
a) Vitamin A
b) Vitamin B
c) Vitamin C
d) Vitamin K
Answer: Vitamin C prevents scurvy.
Q18. Which biomolecule acts as a biological catalyst?
a) Protein
b) Lipid
c) Enzyme
d) Vitamin
Answer: Enzyme acts as a biological catalyst.
Q19. Name the type of bond present between amino acids in proteins.
a) Glycosidic bond
b) Hydrogen bond
c) Peptide bond
d) Ionic bond
Answer: Peptide bond links amino acids in proteins.
Q20. Which biomolecule is the source of steroids and hormones?
a) Protein
b) Carbohydrate
c) Lipid
d) Nucleic acid
Answer: Lipids are the source of steroids and hormones.
Short Answer Questions-Class 12 Chemistry Notes – Biomolecules
Q1. Define monosaccharides with an example.
Answer: Monosaccharides are the simplest form of carbohydrates that cannot be hydrolyzed into simpler sugars. Example: Glucose.
Q2. What are essential amino acids?
Answer: Essential amino acids are those amino acids which cannot be synthesized in the human body and must be obtained from the diet. Example: Lysine, Methionine.
Q3. Write any two functions of lipids.
Answer: Lipids act as energy storage molecules and form structural components of cell membranes.
Q4. What is the primary structure of a protein?
Answer: The primary structure refers to the linear sequence of amino acids in a polypeptide chain linked by peptide bonds.
Q5. What is a non-reducing sugar? Give an example.
Answer: A non-reducing sugar does not have a free aldehyde or ketone group. Example: Sucrose.
Long Answer Questions-Class 12 Chemistry Notes – Biomolecules
Q1. Explain the classification of carbohydrates with examples.
Answer: Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
-
Monosaccharides: Simple sugars like glucose and fructose.
-
Disaccharides: Two monosaccharides linked together; e.g., sucrose, lactose.
-
Oligosaccharides: 2–10 monosaccharides; less common in nature.
-
Polysaccharides: Large complex molecules like starch, glycogen, cellulose.
Q2. Describe the structure of proteins.
Answer: The structure of proteins can be studied at four levels:
-
Primary Structure: Linear sequence of amino acids.
-
Secondary Structure: α-helix and β-pleated sheet arrangements due to hydrogen bonding.
-
Tertiary Structure: 3D folding due to interactions among side chains.
-
Quaternary Structure: Association of multiple polypeptide chains.
Q3. What are nucleic acids? Explain their types and functions.
Answer: Nucleic acids are biomolecules responsible for genetic information storage and transmission.
-
DNA: Stores genetic information.
-
RNA: Helps in protein synthesis and gene expression.
Q4. Write a note on vitamins and their deficiency diseases.
Answer: Vitamins are essential organic compounds required in small quantities for normal metabolism.
-
Vitamin A: Night blindness
-
Vitamin D: Rickets
-
Vitamin C: Scurvy
-
Vitamin K: Blood clotting problems
Q5. Explain the factors affecting enzyme activity.
Answer: Enzyme activity is influenced by:
-
Temperature: Optimal range is needed; very high temperature denatures enzymes.
-
pH: Each enzyme works at a specific pH.
-
Substrate concentration: Higher concentration increases activity until saturation point.
-
Inhibitors: Certain chemicals reduce or stop enzyme activity.
Conclusion
Biomolecules are the fundamental building blocks of life. From providing energy and structure to storing genetic information and catalyzing reactions, they play diverse roles in sustaining life. A clear understanding of biomolecules helps us grasp the chemical processes of living organisms, forming the basis for further studies in biochemistry and molecular biology.