Macromolecules Solved Exercise PTB
Prepare for second-year exams with solved exercises on Macromolecules, following the PTB curriculum. Explore key topics like polymers, structure, and properties of macromolecules for deeper understanding and exam success.
Q. 4 Explain the following terms:
(a) Addition polymer:
An addition polymer is formed by the repeated addition of monomer units with unsaturated bonds (double or triple bonds) without the elimination of any small molecules. Example: Polyethylene from ethene.
(b) Condensation polymer:
A condensation polymer is formed through a condensation reaction, where monomers with two functional groups react, releasing small molecules such as water or HCl. Example: Nylon from hexamethylenediamine and adipic acid.
(c) Thermoplastic:
Thermoplastics are polymers that soften upon heating and harden upon cooling. They can be reshaped multiple times. Example: PVC (Polyvinyl chloride).
(d) Thermosetting plastic:
Thermosetting plastics are polymers that, once set into a given shape through heat, cannot be remelted. Upon reheating, they retain their form or decompose. Example: Bakelite.
Q. 5 Write notes on:
(a) Polyester resins:
Polyester resins are polymers formed by the condensation reaction of polyhydric alcohols with polybasic acids. They are widely used in fiberglass-reinforced products, coatings, and adhesives due to their strength and resistance to corrosion.
(b) Polyamide resins:
Polyamide resins are formed by the condensation reaction of diamines and dicarboxylic acids (e.g., Nylon 6,6). They have high strength, durability, and resistance to chemicals, making them useful in textiles, automotive components, and packaging.
(c) Epoxy resins:
Epoxy resins are formed by the reaction of epoxide compounds with polyamines. They are known for their excellent adhesive properties, resistance to chemicals and heat, and electrical insulation. Epoxy resins are commonly used in coatings, adhesives, and composite materials.
Q. 6 What is the repeating unit in each of the following polymers?
(a) Polystyrene:
Repeating unit: Styrene (C₆H₅-CH=CH₂)
(b) Nylon 6,6:
Repeating unit: Hexamethylenediamine and adipic acid.
(c) Teflon:
Repeating unit: Tetrafluoroethylene (CF₂=CF₂)
(d) Orlon:
Repeating unit: Acrylonitrile (CH₂=CH-CN)
Q. 7 What are carbohydrates and how are they classified?
Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen, usually in the ratio (CH₂O)ₙ. They are an essential source of energy for living organisms. Carbohydrates are classified into three main categories:
- Monosaccharides: Simple sugars, such as glucose and fructose.
- Disaccharides: Composed of two monosaccharides, such as sucrose and lactose.
- Polysaccharides: Long chains of monosaccharides, such as starch, cellulose, and glycogen.
Q. 8 Point out one difference between the compounds in each of the following pairs.
(a) Glucose and fructose:
Glucose is an aldose (contains an aldehyde group), while fructose is a ketose (contains a ketone group).
(b) Sucrose and maltose:
Sucrose is made up of glucose and fructose, while maltose is made up of two glucose molecules.
(c) Cellulose and starch:
Cellulose has β-1,4 glycosidic bonds, while starch has α-1,4 glycosidic bonds.
Q. 9 What are lipids? In what way fats and oils are different?
Lipids are a diverse group of hydrophobic organic compounds, including fats, oils, waxes, and steroids, that are important for energy storage, structural components of cell membranes, and signaling.
- Fats: Solid at room temperature and are primarily composed of saturated fatty acids.
- Oils: Liquid at room temperature and are primarily composed of unsaturated fatty acids.
Q. 10 Define saponification number and iodine number. Discuss the term rancidity.
- Saponification number: The saponification number is the amount of potassium hydroxide (in milligrams) required to saponify 1 gram of fat or oil. It indicates the average molecular weight (chain length) of the fatty acids present.
- Iodine number: The iodine number measures the degree of unsaturation in fats and oils, expressed as the grams of iodine absorbed by 100 grams of fat.
- Rancidity: Rancidity is the process by which fats and oils decompose and develop an unpleasant odor or taste due to oxidation or hydrolysis of the fat molecules. It can be prevented by storing fats in a cool, dark place or using antioxidants.
Q. 11 What is the difference between a glycosidic linkage and a peptide linkage?
- Glycosidic linkage: A glycosidic linkage is a covalent bond that joins a carbohydrate (sugar) molecule to another group (which may or may not be another sugar). Example: Bond between glucose units in starch or cellulose.
- Peptide linkage: A peptide linkage (or peptide bond) is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another amino acid in a protein or peptide chain.
Q. 12 What is the chemical nature of enzymes? Discuss the classification of enzymes.
Enzymes are biological catalysts made of proteins that accelerate biochemical reactions. Some enzymes may also have a non-protein component called a cofactor, which can be a metal ion or an organic molecule (coenzyme).
- Classification of enzymes: Enzymes are classified into six main categories based on the type of reaction they catalyze:
- Oxidoreductases: Catalyze oxidation-reduction reactions.
- Transferases: Transfer functional groups between molecules.
- Hydrolases: Catalyze the hydrolysis of bonds.
- Lyases: Catalyze the addition or removal of groups to form double bonds.
- Isomerases: Catalyze the rearrangement of atoms within a molecule.
- Ligases: Catalyze the joining of two molecules with the input of energy (usually from ATP).
Q. 13 What are nucleic acids? Write down the role of DNA and RNA in life.
- Nucleic acids are large biomolecules composed of nucleotide units. There are two main types of nucleic acids: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).
- Role of DNA: DNA carries genetic information that is passed from one generation to the next. It directs the synthesis of proteins by encoding the necessary instructions for assembling amino acids in the correct order.
- Role of RNA: RNA plays various roles in the cell, primarily involved in protein synthesis. mRNA (messenger RNA) carries genetic information from DNA to the ribosome, rRNA (ribosomal RNA) is a component of the ribosome, and tRNA (transfer RNA) brings amino acids to the ribosome for protein assembly.
