MCQs

The nuclear lamina is an intermediate filament meshwork lining the inner nuclear membrane, providing structural support and anchoring chromatin.

Nuclear pores span the double membrane of the nucleus, serving as controlled gates for macromolecular transit. Plasmodesmata are plant cell junctions.

Chromatin is the relaxed, operational thread-like network of DNA complexed with histone proteins visible during interphase. Chromatids and chromosomes represent highly condensed stages.

The nuclear envelope is structurally characterized as a double-membrane system consisting of an inner and an outer phospholipid bilayer separated by a perinuclear space.

The nucleolus is a dense region within the nucleus dedicated to the transcription of rRNA and structural assembly of ribosomal subunits. The RER and Golgi handle subsequent protein processing, not the synthesis of ribosomes.

Animal cells secrete a protein-rich extracellular matrix (featuring collagen, fibronectin, and laminin) that provides structural support while remaining flexible, unlike the carbohydrate-dominated cell walls of plants.

Auxin stimulates proton pumps to drive H+ into the cell wall; the resulting drop in pH activates expansins, loosening the wall to allow turgor-driven growth.

The mannose-6-phosphate tag acts as a molecular sorting signal that targets newly built hydrolytic enzymes to the lysosome.

The cytoskeletal core forms an internal structural framework that preserves the basic architecture of the cell even when the outer membrane is disrupted.

CESA complexes are hexameric transmembrane rosette assemblies that extrude individual cellulose chains into the extracellular space.

The symplast is the continuous web of living cytoplasm interconnected by plasmodesmata, allowing signaling molecules to travel throughout the plant.

While cellulose is built directly at the plasma membrane, matrix pectins and hemicelluloses are processed in the Golgi and shipped out via vesicles.

Vinculin helps anchor internal actin microfilaments to transmembrane integrins, a structural link required for cell-matrix adhesion and motility.

Expansins disrupt the non-covalent links between cellulose and hemicellulose, allowing turgor pressure to expand the primary cell wall.

Mitochondria contain their own circular genome and ribosomes; mutations in their tRNA disrupt internal protein translation and ATP synthesis.

Pumping protons into the central vacuole lowers its internal pH, creating an acidic environment that powers lysosome-like digestive enzymes.

Cellulase breaks down the cellulose microfibrils, and pectinase dissolves the middle lamella, releasing wall-free protoplasts.

Clathrin is required to structuralize and coat invaginating pits during endocytosis; its absence blocks the internalization of specific ligands.

Inhibiting actin prevents the assembly of the contractile ring, blocking cleavage furrow formation and leaving the cell with two nuclei.