Membrane-Bound Organelles in Eukaryotic Cells

Eukaryotic cells contain many membrane-bound organelles. An organelle is an organized and specialized structure within a living cell. The organelles include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes, mitochondria, and, in plants, chloroplasts.

The nucleus is often referred to as the control center of the eukaryotic cell. This is because it contains the information needed to make proteins. Every part of the cell needs proteins to do its job, so by containing the blueprint to make proteins, the nucleus controls the activities of the other organelles.

Ribosomes are cellular organelles that assemble enzymes and other proteins according to the directions found in the DNA code. Structurally, ribosomes consist of two major subunits. The smaller subunit reads mRNA, and the larger subunit assembles amino acids into a peptide chain that will be folded into a protein.

The endoplasmic reticulum is the site of cellular chemical reactions. It is composed of a series of highly-folded membranes. The endoplasmic reticulum basically functions as a large workspace within the cell. It is folded in this manner to save space. The folds in the endoplasmic reticulum are like the folds of an accordion; if it were not folded, it would take up a tremendous amount of space, but the folds allow a lot of surface area for cellular reactions to fit into a small space. If ribosomes are attached to the endoplasmic reticulum, it is referred to as rough endoplasmic reticulum.

The Golgi apparatus is a flattened system of tubular membranes that modifies proteins to perform certain functions. Proteins are transferred to the Golgi apparatus after being assembled in the ribosomes. After the proteins receive any needed modifications, they are sorted in the Golgi and sent to their appropriate destination. In this way, the Golgi serves as a sort of post office for proteins.

Vacuoles are essentially sacs surrounded by a membrane. They are used by cells as temporary storage sites. They often store food, enzymes, and other materials needed by the cell, and some vacuoles store waste products.