Cell Structure and Function Quiz | Biology MCQs

All cells share universal core components that support life: a plasma membrane for boundary control, cytoplasm for biochemical activity, ribosomes for protein synthesis, dissolved enzymes for metabolism, water for fluid medium, and DNA for hereditary information. Specialized organelles appear only in certain cell types.

Prokaryotes lack membrane-bound organelles like nuclei and mitochondria. Instead, they contain a nucleoid holding circular DNA and may possess structures like pili, flagella, or a cell wall. These enable survival, movement, and attachment without eukaryotic compartmentalization.

The four eukaryotic kingdoms—Protist, Plantae, Fungi, and Animalia—contain organisms whose cells have nuclei and membrane-bound organelles. Bacteria and Archaea are prokaryotic domains, and viruses are acellular, so they are not included in eukaryotic classification.

Compartmentalization increases efficiency by allowing specific reactions to occur in specialized regions. It improves organization, prevents interference between pathways, and increases surface area for reactions like metabolism and transport, enhancing overall cellular function and adaptability.

The rough ER contains ribosomes that synthesize proteins destined for secretion, membranes, or organelles. Its structure supports proper folding, modification, and packaging upstream of Golgi transport, making it essential for the cell’s protein production pipeline.

Cotranslational transport couples translation with translocation into the ER. As the signal sequence emerges from the ribosome, it directs the ribosome–nascent chain complex to the ER, ensuring proteins enter the ER lumen or membrane during synthesis, not afterward.

The Golgi uses vesicular transport to move cargo forward (cis to trans) and cisternal maturation where cisternae themselves change identity while enzymes move backward. Together, they ensure correct modification, sorting, and delivery of proteins throughout the cell.

Protein destination is determined by carbohydrate tags added in the Golgi. These tags act like molecular labels directing proteins to lysosomes, membranes, or secretion pathways. Without correct tagging, proteins risk mislocalization and loss of function.

Lysosomes house acidic hydrolases that break down macromolecules, cellular debris, and pathogens. Their internal low pH, maintained by proton pumps, activates digestive enzymes and ensures controlled degradation without harming the cytosol.

Peroxisomes oxidize fatty acids and neutralize toxins via enzymes like catalase. They prevent oxidative damage by detoxifying hydrogen peroxide, contributing to lipid metabolism and cellular protection, especially in liver and kidney cells.

Both mitochondria and chloroplasts contain their own circular DNA, supporting their evolutionary origin as independent prokaryotes. Their genes encode essential proteins for respiration or photosynthesis, allowing semi-autonomous functioning within eukaryotic cells.

Endosymbiosis proposes mitochondria and chloroplasts originated from engulfed bacteria. These bacteria provided metabolic benefits, eventually forming symbiotic organelles. Evidence includes double membranes, circular DNA, and similarities to bacterial ribosomes.

The cytoskeleton is built from microfilaments for movement, intermediate filaments for tension resistance, and microtubules for compression resistance and intracellular transport. Together they shape the cell, enable motility, and organize organelles.

Microfilaments form thin, flexible actin strands, intermediate filaments provide tensile strength, and microtubules form hollow tubes resisting compression and supporting vesicle movement. Each contributes uniquely to cell structure, dynamics, and division.

Dynein and kinesin move along microtubules in opposite directions: dynein to the − end toward the cell body, kinesin to the + end toward the periphery. This polarity underlies coordinated vesicle transport and flagellar motion patterns.

Griffith demonstrated transformation when harmless R bacteria acquired genetic material from heat-killed S bacteria, restoring virulence. This revealed a “transforming principle,” later identified as DNA, marking a foundational discovery in molecular genetics.

Avery’s knockout experiments used enzymes to remove proteins, RNA, or DNA from S strain extracts. Only DNA removal prevented transformation, proving DNA—not protein—was the hereditary molecule responsible for Griffith’s observed effects.

Hershey and Chase used radioactive labels (^32P for DNA, ^35S for protein) in bacteriophages. Only DNA entered host cells and directed viral replication, establishing DNA—not protein—as the genetic material.

The three DNA replication models—conservative, semiconservative, and dispersive—proposed differing strand inheritance patterns. Semiconservative replication, later proven correct, produces daughter molecules with one old and one new strand.

Meselson and Stahl labeled DNA with heavy and light nitrogen, then used density centrifugation to observe hybrid and light bands. Data confirmed semiconservative replication because each generation produced predictable density patterns matching the model.

DNA polymerase adds nucleotides to the 3′ end, following 5′→3′ synthesis, complementarity, and antiparallel strand arrangement. These rules ensure accurate replication and proper base pairing along both leading and lagging strands.

Prokaryotes have circular DNA with one origin and two forks, while eukaryotes possess multiple origins and linear chromosomes. Both use leading/lagging synthesis, but eukaryotic replication is more complex due to chromatin structure.

The leading strand synthesizes continuously toward the fork, while the lagging strand synthesizes away in short Okazaki fragments requiring primase, ligase, and polymerase coordination. These differences arise from antiparallel strand orientation.

DNA replication relies on helicase (unwinds), single-strand binding proteins (stabilize), primase (RNA primers), polymerase (elongation), and ligase (joins fragments). Each enzyme plays a precise role to ensure accurate and continuous synthesis.

Telomerase extends the 3′ end using its internal RNA template, allowing polymerase to fill in complementary DNA. This prevents telomere erosion and preserves chromosome stability through repeated extension and priming cycles.

Cell division includes DNA replication during interphase, chromosome segregation to opposite poles, and cytoplasmic division by cytokinesis. These steps ensure faithful genetic transmission and formation of two genetically identical daughter cells.

G1 involves growth and preparation, S is DNA synthesis, G2 completes preparation for mitosis, and M executes division. These stages correlate with characteristic curve segments reflecting DNA content and cell cycle progression.