MCQs

mRNA must exit the nucleus to be translated into protein. Blocking export stalls translation in the cytoplasm.

Cyclin-dependent kinases phosphorylate nuclear lamins, causing the intermediate filaments to depolymerize and dismantle the nuclear structural border.

Nucleolar Organizer Regions (NORs) contain the repeating loops of DNA encoding rRNA genes around which the nucleolus forms.

Proteins destined for the nucleus possess a Nuclear Localization Signal (NLS) that is recognized by importin proteins for active transport through the pore.

Karyolymph or nucleoplasm fluid forms the soluble matrix inside the nucleus, supporting chemical activities.

Heterochromatin is tightly packed, dark-staining, and transcriptionally silent, whereas euchromatin is loosely packed and active.

High protein synthesis demands rapid ribosome production, which directly causes the hypertrophy of the nucleolus to produce rRNA.

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.