Class 10 Chemistry — Chapter 13: Biochemistry

Board: Federal Board

1. Multiple Choice Questions (MCQs)

i. Which of the following is NOT a function of proteins in the body?

a) Acting as enzymes
b) Storing genetic information
c) Providing structural support
d) Transporting molecules

Correct Answer: (b) Storing genetic information

Concept: Proteins serve as enzymes, structural components (collagen and keratin), and transport molecules (hemoglobin). However, genetic information is stored and transmitted by nucleic acids (DNA and RNA).

ii. Which of the following best describes proteins?

a) Polysaccharides
b) Polymers of amino acids
c) Chains of fatty acids
d) Simple sugars

Correct Answer: (b) Polymers of amino acids

Concept: Proteins are large macromolecules (polymers) built by linking numerous amino acid monomers through peptide bonds.

iii. Which bond is responsible for linking amino acids together in a protein?

a) Hydrogen bond
b) Peptide bond
c) Ionic bond
d) Covalent bond

Correct Answer: (b) Peptide bond

Concept: A peptide bond is a specialized covalent amide bond formed between the carboxyl group of one amino acid and the amino group of another, with the elimination of a water molecule.

iv. Which of the following is a component of nucleic acids?

a) Amino acid
b) Fatty acid
c) Phosphate group
d) Glucose

Correct Answer: (c) Phosphate group

Concept: Nucleotides, the building blocks of nucleic acids, consist of three parts: a pentose sugar, a nitrogenous base, and a phosphate group.

v. Which of the following is a characteristic of vitamins?

a) They provide energy directly.
b) They are essential for normal body function.
c) They are inorganic molecules.
d) They are a primary source of protein.

Correct Answer: (b) They are essential for normal body function.

Concept: Vitamins are organic micronutrients that do not yield energy directly but are vital cofactors for metabolic and physiological functions.

vi. Which vitamin is important for vision and immune function and is fat-soluble?

a) Vitamin C
b) Vitamin B12
c) Vitamin A
d) Vitamin K

Correct Answer: (c) Vitamin A

Concept: Vitamin A (retinol) is a fat-soluble vitamin crucial for low-light vision, cellular differentiation, and immune health.

vii. Which acid carries genetic information?

a) Amino acid
b) Nucleic acid
c) Sulphuric acid
d) Ascorbic acid

Correct Answer: (b) Nucleic acid

Concept: Deoxyribonucleic acid (DNA), a type of nucleic acid, serves as the primary repository of hereditary information in living organisms.

viii. Which vitamin helps the body absorb calcium and is fat-soluble?

a) Vitamin B12
b) Vitamin C
c) Vitamin D
d) Vitamin E

Correct Answer: (c) Vitamin D

Concept: Vitamin D is a fat-soluble secosteroid that promotes intestinal absorption of calcium and phosphorus, helping maintain strong bones.

ix. Which of the following is a primary function of lipids in the body?

a) Providing immediate energy
b) Storing genetic information
c) Long-term energy storage
d) Catalyzing biochemical reactions

Correct Answer: (c) Long-term energy storage

Concept: Fats and oils (lipids) store more than double the energy per gram compared to carbohydrates, making them ideal for compact, long-term energy storage and thermal insulation.

x. How might a diet lacking in lipids affect the absorption of certain vitamins?

a) It would have no effect since vitamins are not related to lipids.
b) It would increase absorption because lipids compete with vitamins for absorption.
c) It would decrease the absorption of fat-soluble vitamins, such as A, D, E, and K.
d) It would decrease the absorption of water-soluble vitamins, such as C and B.

Correct Answer: (c) It would decrease the absorption of fat-soluble vitamins, such as A, D, E, and K.

Concept: Fat-soluble vitamins require dietary fats and micelles for emulsification and efficient absorption across the intestinal mucosa.

xi. Which vitamin is essential for blood clotting?

a) Vitamin A
b) Vitamin C
c) Vitamin D
d) Vitamin K

Correct Answer: (d) Vitamin K

Concept: Vitamin K is a necessary cofactor for the hepatic synthesis of clotting factors, such as prothrombin, required for blood coagulation.

xii. Which biochemistry application is used to determine parentage?

a) Pregnancy test
b) Genetic engineering
c) Cancer screening
d) Parental genetic testing

Correct Answer: (d) Parental genetic testing

Concept: DNA fingerprinting and parental genetic testing compare specific polymorphic regions of DNA to establish biological relationships.

2. Short Questions

i. How does the body make protein?

Answer: Proteins are synthesized through gene expression in cells. Transcription copies genetic codes from DNA to messenger RNA (mRNA) in the nucleus. Translation occurs at ribosomes in the cytoplasm, where transfer RNA (tRNA) brings specific amino acids matching the mRNA codons. These amino acids join together through peptide bonds to form proteins.

ii. What do vitamins do for our body?

Answer: Vitamins act as essential coenzymes and regulators in metabolic processes. They support immune defence, maintain healthy skin, vision, and bones, protect cells from oxidative stress, and assist in energy metabolism and blood coagulation.

iii. How do parents protect their children from genetic disorders?

Answer: Parents can minimize risks through genetic counselling, carrier screening before conception, prenatal testing (such as amniocentesis during pregnancy), and lifestyle choices that reduce exposure to mutagenic substances.

iv. Differentiate between genetic engineering and gene therapy.

Answer:

• Genetic Engineering: Involves the direct manipulation, insertion, or deletion of genes in an organism’s genome, often across species, to modify traits. An example is genetically modified (GMO) crops.

• Gene Therapy: Specifically focuses on introducing, altering, or replacing defective genes inside human patient cells to treat or cure genetic diseases.

v. How is gene cloning different from therapeutic cloning?

Answer:

• Gene Cloning: Involves isolating and replicating a specific DNA segment or gene using vectors, such as plasmids, inside host cells.

• Therapeutic Cloning: Creates cloned embryos through somatic cell nuclear transfer (SCNT) to harvest stem cells for treating medical conditions and regenerating damaged tissues.

vi. Explain why proteins are considered natural polyamides.

Answer: Proteins possess repeating amide linkages (peptide bonds, \(-CONH-\)) along their backbone structure. These linkages are formed between amino and carboxyl groups, structurally categorizing proteins as natural condensation polymers or polyamides.

vii. How do pregnancy tests use biochemical principles to detect pregnancy?

Answer: Home pregnancy tests use immunoassay strips containing monoclonal antibodies targeted against Human Chorionic Gonadotropin (hCG), a hormone produced by the placenta shortly after implantation. A colourimetric reaction confirms the presence of hCG in urine.

viii. Evaluate the role of nucleic acids in heredity and cell function.

Answer: DNA stores and passes hereditary instructions across generations, while various forms of RNA (mRNA, tRNA, and rRNA) translate this genetic blueprint into functional proteins that catalyse and regulate cellular activities.

3. Long Questions

i. What is the significance of nucleic acids as information-carrying molecules?

Answer: Nucleic acids (DNA and RNA) are biopolymers composed of nucleotide monomers. DNA maintains the stable, long-term genetic blueprint of organisms, ensuring faithful replication during cell division. RNA intermediates transcribe and translate this coded information into structural and functional proteins, which determine cellular characteristics and metabolism.

ii. Compare and contrast the functions and properties of lipids and carbohydrates.

Answer:

Carbohydrates:

• Composed of carbon, hydrogen, and oxygen, generally in a 1:2:1 ratio.

• Serve as immediate energy sources, such as glucose.

• Also perform structural functions, such as cellulose in plants.

• Are soluble in polar solvents like water.

Lipids:

• Composed of higher proportions of carbon-hydrogen bonds with fewer oxygen atoms.

• Provide high-density, long-term energy storage.

• Provide thermal insulation and form cellular membrane structures, such as phospholipids.

• Also perform hormonal signalling functions, such as steroids.

• Are hydrophobic and insoluble in water.

iii. Why is protein structure important?

Answer: Protein function depends entirely on its three-dimensional conformation across four structural levels:

1. Primary Structure: The linear sequence of amino acids.

2. Secondary Structure: Local folding patterns, such as alpha-helix and beta-sheet, stabilized by hydrogen bonds.

3. Tertiary Structure: Overall three-dimensional folding driven by interactions between R-groups.

4. Quaternary Structure: Association of multiple polypeptide subunits.

A disruption or mutation in protein structure, including denaturation, can lead to a complete loss of biological activity.

iv. Explain the significance of amino acids in living organisms.

Answer: Amino acids are organic molecules containing an amino group, a carboxyl group, and a variable side chain (R-group).

Beyond serving as building blocks for proteins, specific amino acids perform other important functions. They act as neurotransmitters, such as glutamate and GABA, precursors for hormones and nucleotides, and metabolic intermediates in energy pathways.

v. Explain the process of cloning in biochemistry.

Answer: Gene cloning typically involves the following steps:

1. Isolation of the Target Gene: The gene of interest is isolated.

2. Insertion into a Vector: The gene is inserted into a vector, such as a plasmid, using restriction enzymes and DNA ligase.

3. Introduction into a Host: The recombinant vector is introduced into a host organism, such as E. coli.

4. Culturing Host Cells: The host cells are cultured to produce numerous identical copies of the target gene or its expressed protein product.

vi. What is the difference between genetic engineering and gene therapy?

Answer:

• Genetic Engineering: It is a broad biotechnological discipline that involves altering genomes across plants, animals, and microbes for agricultural, industrial, or research purposes.

• Gene Therapy: It is a specialized medical application aimed at correcting pathological genetic defects in human somatic cells to restore normal physiological function.

vii. Why are vitamins essential to human health? Provide two examples with their functions.

Answer: Vitamins are essential because the human body cannot synthesize them in sufficient quantities, except for limited synthesis of certain vitamins, such as Vitamin D through the skin and Vitamin K by gut flora. Therefore, they must be obtained through the diet. They act as regulatory coenzymes and support various body functions.

Examples:

1. Vitamin C (Ascorbic Acid): Essential for collagen synthesis, antioxidant defence, and wound healing.

2. Vitamin D: Essential for calcium homeostasis and bone mineralization.

viii. Compare and contrast the uses and functions of proteins, carbohydrates, and lipids.

Answer:

• Proteins: Perform catalytic functions as enzymes, provide structural support, transport substances, and help in defence.

• Carbohydrates: Provide immediate cellular energy and contribute to structural integrity.

• Lipids: Serve as long-term energy reserves, form cellular membrane bilayers, and provide protective padding and insulation.

4. Think Tank

1. What is the importance of carbohydrates in maintaining energy levels?

Answer: Carbohydrates break down rapidly into glucose, which enters cellular respiration to generate ATP (adenosine triphosphate). This makes them the primary and most accessible energy source for daily metabolic demands, particularly for high-energy organs like the brain and active skeletal muscles.

2. What is the difference between genetic engineering and gene therapy?

Answer: Genetic engineering broadly modifies or introduces genes across diverse biological systems to produce desired traits. In contrast, gene therapy is strictly therapeutic and focuses on treating inherited or acquired genetic disorders in human patients.

Notes by Sir Dilawar
For more notes, visit QuranEducationPoint.com