MCQs

Cisternae are the flattened fluid-filled sacs making up the ER and Golgi. Cristae belong to mitochondria, and thylakoids belong to chloroplasts.

The smooth endoplasmic reticulum (SER) lacks ribosomes and contains the specialized enzymatic machinery necessary for lipid and steroid metabolism.

The membrane network of the endoplasmic reticulum shares physical continuity with the outer nuclear membrane, allowing structural integration.

The rough endoplasmic reticulum (RER) derives its descriptive name directly from the attachment of membrane-bound ribosomes on its outer cytosolic side.

Because mRNA is kept away from ribosomes during synthesis, the cell can safely carry out splicing and capping before protein translation starts.

Exportins recognize cargo proteins tagged with an NES and form a complex with Ran-GTP to migrate out of the nucleus.

Euchromatin is the loosely packed, accessible form of DNA where RNA polymerase can readily bind to transcribe structural genes.

The inner nuclear membrane contains integral proteins (like LBR) that bind to the nuclear lamina to stabilize chromatin positioning.

Emerin is a vital inner nuclear membrane protein that anchors the nuclear lamina. Its loss disrupts nuclear structure, causing Emery-Dreifuss muscular dystrophy.

Nuclear transport does not use direct ATP/GTP hydrolysis at the transporter; instead, it relies on high Ran-GTP inside the nucleus and low Ran-GTP in the cytosol to maintain directionality.

Ran-GAP converts Ran-GTP to Ran-GDP in the cytosol, releasing importin to capture new cargo. Without it, the concentration gradient collapses, halting transport.

FG-nucleoporins (Phenylalanine-Glycine repeats) form a chaotic, flexible brush-like gel structure inside the pore that blocks large unchaperoned molecules.

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.