Cell Division
Short Questions
1. What are biomolecules?
Answer: Biomolecules are organic molecules essential for life processes, including carbohydrates, proteins, lipids, and nucleic acids.
2. What is the hydrogen-to-oxygen ratio in carbohydrates?
Answer: The hydrogen-to-oxygen ratio in carbohydrates is 2:1.
3, Name a pentose sugar found in RNA.
Answer: Ribose is a pentose sugar found in RNA.
4. What type of bond links monosaccharides in disaccharides?
Answer: A glycosidic bond links monosaccharides in disaccharides.
5. Which polysaccharide forms the cell walls in plants?
Answer: Cellulose forms the cell walls in plants.
6. What distinguishes saturated fatty acids from unsaturated ones?
Answer: Saturated fatty acids have no double bonds, while unsaturated fatty acids have one or more double bonds.
7. Name a simple protein found in egg white.
Answer: Albumin is a simple protein found in egg white.
8. What is the secondary structure of a protein?
Answer: The secondary structure involves alpha-helix or beta-pleated sheets formed by hydrogen bonds in a polypeptide chain.
9. Which base is unique to DNA compared to RNA?
Answer: Thymine is unique to DNA, replaced by uracil in RNA.
10. What is the function of tRNA?
Answer: tRNA transfers amino acids to ribosomes during protein synthesis.
11. What is an enzyme’s substrate?
Answer: The substrate is the specific molecule an enzyme acts upon.
12. What is the optimal pH for pepsin?
Answer: The optimal pH for pepsin is 2 (acidic).
13. What is a metabolic pool?
Answer: A metabolic pool is a reservoir of biomolecules in a cell for enzymatic reactions.
14. Name a secondary metabolite used as a pain reliever.
Answer: Morphine is a secondary metabolite used as a pain reliever.
15. What reagent tests for reducing sugars?
Answer: Benedict’s reagent tests for reducing sugars.
Long Questions
1. What are the classes of carbohydrates, and provide examples for each?
Answer: Carbohydrates are classified into monosaccharides, disaccharides, and polysaccharides based on sugar unit count. Monosaccharides, like glucose and fructose, are single sugar units; disaccharides, such as sucrose (glucose + fructose) and lactose, consist of two units; and polysaccharides, like starch and cellulose, are long chains of monosaccharides. These serve as energy sources, structural components, and storage molecules in organisms.
2. Explain the biological roles of carbohydrates in living organisms.
Answer: Carbohydrates provide energy, with glucose being the primary substrate for ATP production through cellular respiration. They also serve structural roles, as seen in cellulose forming plant cell walls, and act as storage molecules, like starch in plants and glycogen in animals. Additionally, lactose in milk supplies energy to infants, supporting growth.
3. Differentiate between saturated and unsaturated fatty acids with examples.
Answer: Saturated fatty acids lack double bonds in their hydrocarbon chains, making them solid at room temperature, e.g., stearic acid in animal fats. Unsaturated fatty acids have one or more double bonds, typically liquid, e.g., linoleic acid in seed oils. These structural differences influence their roles in energy storage and membrane fluidity.
4. Describe the structure and role of phospholipids in cell membranes.
Answer: Phospholipids consist of glycerol, two fatty acids, and a phosphate group, forming a hydrophilic head and hydrophobic tails. In cell membranes, they arrange into a bilayer, with heads facing water and tails inward, creating a selective barrier. This structure regulates the movement of substances, maintaining cellular integrity.
5. What is the significance of the secondary structure in proteins?
Answer: The secondary structure of proteins, involving alpha-helices or beta-pleated sheets stabilized by hydrogen bonds, provides stability and shape to the polypeptide chain. Examples include keratin (alpha-helix) in hair and silk fibroin (beta-sheet) in silk. This structure is critical for the protein’s functional conformation and interactions.
6. Explain the Watson and Crick model of DNA structure.
Answer: Watson and Crick described DNA as a double helix with two antiparallel polynucleotide strands linked by hydrogen bonds (adenine-thymine, guanine-cytosine). The sugar-phosphate backbone forms the exterior, with bases paired inside, one turn spanning 34 Å. This structure ensures genetic stability and enables accurate replication.
7. What are the types of RNA, and what roles do they play in cells?
Answer: RNA includes messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). mRNA carries genetic instructions for protein synthesis, rRNA forms the structural core of ribosomes, and tRNA delivers amino acids to ribosomes during translation. These RNAs are essential for gene expression and protein production.
8. Describe the induced fit model of enzyme action.
Answer: The induced fit model, proposed by Koshland, suggests that an enzyme’s active site flexibly reshapes to fit the substrate upon binding, enhancing catalytic efficiency. This contrasts with the rigid lock-and-key model, emphasizing enzyme adaptability. It explains the high specificity and effectiveness of enzymatic reactions.
9. What is the metabolic pool, and why is it significant in cells?
Answer: The metabolic pool is a dynamic reservoir of biomolecules in a cell, available for enzymatic reactions to meet cellular needs. It allows interconversion, such as carbohydrates to lipids, ensuring flexibility in metabolism. This balance between catabolic and anabolic pathways maintains cellular homeostasis.
10. How do secondary metabolites contribute to human welfare?
Answer: Secondary metabolites, such as morphine, are used in medicine to treat pain and diseases like cancer. They enhance food flavors (e.g., glucosinolates in cabbage) and serve as preservatives due to their antibiotic properties. In agriculture, compounds like tannins protect crops from pests, improving yield and quality.
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