MCQs

Transmembrane proteins are threaded into the RER membrane during translation, moving via vesicles through the secretory pathway to reach the plasma membrane.

A core carbohydrate tree is built on dolichol phosphate, a membrane lipid anchor, before being transferred to an asparagine residue of the growing peptide.

The Unfolded Protein Response (UPR) activates signaling loops to expand ER volume, increase chaperone expression, and halt translation to manage stress.

The Lys-Asp-Glu-Leu (KDEL) sequence at the C-terminus of ER-resident proteins ensures they are captured and recycled back if they escape to the Golgi.

The Signal Recognition Particle (SRP) binds the emerging N-terminal signal sequence of a peptide, stalling translation until it docks with the RER membrane.

The sarcoplasmic reticulum is a specialized SER that hoards calcium ions, releasing them into the sarcoplasm to trigger muscle contraction.

The SER contains the Cytochrome P450 enzyme family, which hydroxylates hydrophobic compounds to increase solubility and ease excretion.

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.