Eukaryotic Cell Structure: The Nucleus, Ribosomes, and the Endomembrane System

Vocabulary flashcards covering the structure and function of the nucleus, ribosomes, and endoplasmic reticulum in eukaryotic cells.

Nuclear envelope

A structure composed of two lipid bilayer membranes that encloses the nucleus in eukaryotic cells, separating its contents from the cytoplasm.

Nuclear pore complex

A protein-lined channel in the nuclear envelope that regulates the transport of molecules between the nucleus and the cytoplasm.

Nucleolus

A prominent structure within the nucleus of eukaryotic cells that primarily functions in the assembly of ribosomes.

Nuclear lamina

A dense fibrillar network composed of intermediate filaments and membrane-associated proteins situated on the inner surface of the nuclear envelope.

Chromatin

A complex of DNA and proteins that condenses to form chromosomes within the nucleus of eukaryotic cells.

Ribosomes

Cellular structures composed of ribosomal RNAs (rRNAs) and proteins that carry out protein synthesis.

Free ribosomes

Ribosomes suspended in the cytosol that synthesize proteins functioning within the cytosol.

Bound ribosomes

Ribosomes attached to the exterior of the endoplasmic reticulum (ER) or nuclear envelope that synthesize proteins destined for insertion into membranes or packaging within organelles.

Endomembrane system

A network of membrane-bound structures in eukaryotic cells—including the nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, plasma membrane, and vesicles—that are connected continuously or via vesicle transport, excluding plastids and mitochondria.

Endoplasmic reticulum (ER)

An extensive network of membranes continuous with the nuclear envelope, accounting for more than half of the total membrane in many eukaryotic cells.

Rough ER

A region of the endoplasmic reticulum studded with ribosomes on its outer surface, involved in the modification and folding of proteins and membrane manufacturing.

Smooth ER

A region of the endoplasmic reticulum lacking ribosomes, involved in lipid and steroid synthesis, carbohydrate metabolism regulation, drug detoxification, and calcium ion storage.

Sarcoplasmic reticulum

A specialized form of smooth endoplasmic reticulum found in muscle cells that functions specifically in storing calcium ions ($Ca^{2+}$).