Biomolecules – Complete Notes (Carbohydrates, Proteins, Nucleic Acids, Vitamins & Enzymes)
Biomolecules are the essential organic compounds that form the basis of life. They are present in all living organisms and are responsible for various structural, functional, and regulatory processes. In this article, we will study Carbohydrates, Proteins, Nucleic Acids, Vitamins, and Enzymes from basic to advanced level, which is highly useful for NEET and Chemistry students.
1. Carbohydrates
Carbohydrates are polyhydroxy aldehydes or ketones or compounds that yield them on hydrolysis. They are the primary source of energy in living organisms and constitute a major part of our diet.
Classification of Carbohydrates
- Monosaccharides – Simple sugars that cannot be hydrolyzed further (e.g., Glucose, Fructose, Galactose).
- Disaccharides – Formed by condensation of two monosaccharides (e.g., Sucrose, Maltose, Lactose).
- Polysaccharides – Long chains of monosaccharide units (e.g., Starch, Glycogen, Cellulose).
Important Carbohydrates
Glucose (C6H12O6)
It is an aldohexose and the most important energy source in cells. It exists in cyclic and open-chain forms.
Fructose
A ketohexose found in fruits and honey. It is sweeter than glucose.
Starch
Storage carbohydrate in plants, composed of amylose (linear) and amylopectin (branched).
Glycogen
Storage carbohydrate in animals, highly branched, also known as animal starch.
Cellulose
Main structural component of plant cell walls. It is a polymer of β-D-glucose and indigestible to humans.
2. Proteins
Proteins are polymers of amino acids linked by peptide bonds. They perform structural, catalytic, hormonal, and transport functions in the body.
Amino Acids
Amino acids are the building blocks of proteins. They contain an amino group (-NH2) and a carboxylic group (-COOH). In humans, 20 standard amino acids exist, classified into:
- Essential amino acids – must be obtained from diet (e.g., Valine, Leucine, Lysine).
- Non-essential amino acids – synthesized by the body (e.g., Glycine, Alanine).
Peptide Bond
The bond between the amino group of one amino acid and the carboxyl group of another, releasing water.
Levels of Protein Structure
- Primary structure – sequence of amino acids.
- Secondary structure – α-helix or β-pleated sheet formed by hydrogen bonding.
- Tertiary structure – 3D folding stabilized by disulfide bonds, hydrophobic interactions.
- Quaternary structure – association of multiple polypeptide chains (e.g., Hemoglobin).
3. Nucleic Acids
Nucleic acids are biopolymers of nucleotides. They store and transmit genetic information.
Components of Nucleotides
- Nitrogenous base – Purines (Adenine, Guanine), Pyrimidines (Cytosine, Thymine, Uracil).
- Pentose sugar – Ribose (RNA) or Deoxyribose (DNA).
- Phosphate group.
DNA (Deoxyribonucleic Acid)
DNA carries genetic information. It is a double helix structure proposed by Watson and Crick in 1953. Complementary base pairing: A–T and G–C.
RNA (Ribonucleic Acid)
RNA helps in protein synthesis. Types include mRNA, tRNA, and rRNA.
4. Vitamins
Vitamins are organic compounds required in small amounts for proper metabolism. They are classified as:
| Vitamin | Type | Function | Deficiency Disease |
|---|---|---|---|
| A | Fat-soluble | Vision, growth | Night blindness |
| D | Fat-soluble | Calcium absorption | Rickets |
| E | Fat-soluble | Antioxidant | Infertility |
| K | Fat-soluble | Blood clotting | Excessive bleeding |
| B Complex | Water-soluble | Metabolism | Beri-Beri, Pellagra |
| C | Water-soluble | Collagen synthesis | Scurvy |
5. Enzymes
Enzymes are biological catalysts that increase the rate of biochemical reactions without being consumed. They are mostly proteins (some are RNA-based, called ribozymes).
Characteristics of Enzymes
- Highly specific in action.
- Work under mild temperature and pH.
- Can be regulated by inhibitors or activators.
Mechanism of Enzyme Action
Enzymes lower activation energy. Substrate binds to the active site of the enzyme, forming an enzyme-substrate complex, which then converts to product.
Factors Affecting Enzyme Activity
- Temperature
- pH
- Substrate concentration
- Presence of inhibitors
Conclusion
Biomolecules are fundamental to life, serving as the building blocks and functional molecules in living organisms. From energy storage (carbohydrates), structural and functional roles (proteins), genetic information storage (nucleic acids), regulation (vitamins), to catalysis (enzymes), biomolecules form the very basis of biochemistry. A strong understanding of these concepts is essential for competitive exams like NEET and for advanced studies in chemistry and biology.
Biomolecules – Important MCQs for NEET
Practice the following MCQs on Carbohydrates, Proteins, Nucleic Acids, Vitamins & Enzymes. Click on the button to reveal the correct answer with explanation.
Q1. Glucose is classified as:
- A) Aldopentose
- B) Aldohexose
- C) Ketohexose
- D) Ketopentose
Explanation: Glucose has six carbons (hexose) and contains an aldehyde group, hence it is an aldohexose.
Q2. Fructose is commonly known as:
- A) Blood sugar
- B) Milk sugar
- C) Fruit sugar
- D) Cane sugar
Explanation: Fructose is a ketohexose found in fruits and honey, hence called fruit sugar.
Q3. The storage carbohydrate in animals is:
- A) Starch
- B) Cellulose
- C) Glycogen
- D) Fructose
Explanation: Animals store glucose in the form of glycogen, also called animal starch.
Q4. Which polysaccharide forms the cell wall of plants?
- A) Amylose
- B) Cellulose
- C) Glycogen
- D) Sucrose
Explanation: Cellulose is a β-D-glucose polymer and the main structural component of plant cell walls.
Q5. Proteins are polymers of:
- A) Nucleotides
- B) Monosaccharides
- C) Amino acids
- D) Fatty acids
Explanation: Proteins are formed by peptide bonds between amino acids.
Q6. The bond linking two amino acids is called:
- A) Hydrogen bond
- B) Peptide bond
- C) Glycosidic bond
- D) Phosphodiester bond
Explanation: A peptide bond forms between the –COOH of one amino acid and –NH₂ of another.
Q7. Which is an essential amino acid?
- A) Glycine
- B) Valine
- C) Alanine
- D) Serine
Explanation: Essential amino acids cannot be synthesized by the body and must be taken from food.
Q8. The hereditary material in most organisms is:
- A) DNA
- B) RNA
- C) Protein
- D) Lipid
Explanation: DNA stores genetic information, except in some viruses where RNA is genetic material.
Q9. In DNA, adenine pairs with:
- A) Cytosine
- B) Guanine
- C) Thymine
- D) Uracil
Explanation: According to Watson-Crick base pairing, A–T (2 H-bonds) and G–C (3 H-bonds).
Q10. Which RNA carries amino acids to ribosomes?
- A) mRNA
- B) rRNA
- C) tRNA
- D) snRNA
Explanation: Transfer RNA (tRNA) carries specific amino acids to the ribosome for protein synthesis.
Q11. Vitamin D deficiency causes:
- A) Night blindness
- B) Scurvy
- C) Rickets
- D) Pellagra
Explanation: Vitamin D helps in calcium absorption; its deficiency leads to weak bones and rickets in children.
Q12. Vitamin C deficiency leads to:
- A) Pellagra
- B) Beri-beri
- C) Scurvy
- D) Anemia
Explanation: Vitamin C is essential for collagen synthesis; deficiency causes bleeding gums and scurvy.
Q13. Which vitamin is also called Retinol?
- A) Vitamin A
- B) Vitamin B1
- C) Vitamin E
- D) Vitamin K
Explanation: Vitamin A is known as retinol, required for vision and skin health.
Q14. Enzymes are mostly:
- A) Lipids
- B) Proteins
- C) Carbohydrates
- D) Nucleic acids
Explanation: Most enzymes are proteins except some ribozymes (RNA molecules with catalytic activity).
Q15. The bond between nucleotides in DNA is:
- A) Peptide bond
- B) Glycosidic bond
- C) Phosphodiester bond
- D) Hydrogen bond
Explanation: Nucleotides are linked by phosphodiester bonds between phosphate and sugar groups.
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