Endomembrane System - Structures & Functions | Chapter 4.4

Endomembrane System

A system in eukaryotic cells that includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane. These components are either continuous or connected through transfer by vesicles.

Endoplasmic Reticulum (ER)

A network of membranes that accounts for more than half of the total membrane in eukaryotic cells. It is continuous with the nuclear envelope and can be classified into smooth ER (lacks ribosomes) and rough ER (surface is studded with ribosomes).

Smooth ER

A type of ER that synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, and stores calcium ions.

Rough ER

A type of ER that has bound ribosomes, which secrete glycoproteins. It distributes transport vesicles and protein vesicles and serves as the membrane factory of the cell.

Lysosomes

Membranous sacs containing hydrolytic enzymes that digest macromolecules. Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids. They work best in the acidic environment inside the lysosome and fuse with food vacuoles to digest molecules.

Vacuoles

Large vesicles derived from the ER and Golgi apparatus. They can serve different functions, such as food vacuoles (created from phagocytosis) and contractile vacuoles (pump excess water out of the cell). Certain vacuoles in plants and fungi also carry out enzymatic hydrolysis like lysosomes.

Golgi Apparatus

Consists of membranous sacs called cisternae. It modifies products of the ER, manufactures certain macromolecules, and sorts and packages materials into transport vesicles.