Eukaryotic Cells: Structure, Organelles and Functions

Eukaryotic Cells

Eukaryotic cells have a defined nucleus and various membrane-bound organelles.

Animal and Plant Cells

In animal cells, there are centrioles arranged in cylinders, also called centrosomes. In plant cells, there is a cell wall that protects the cell. Plant cells also have plasmodesmata, channels that connect one cell to another, and tend to contain large vacuoles and chloroplasts.

Cell Components

Nucleus

The nuclear envelope is a double membrane separated by an intermembrane space. Both membranes are crossed by nuclear pores.

• Nucleoplasm: an aqueous medium in which the nuclear components, such as DNA, are immersed.
• Nucleolus: a spherical body lacking a membrane. It can only be seen when the cell is not dividing.
• Chromatin: made up of DNA filaments.

Cytokinesis

In cytokinesis, animal cells divide by cleavage, a constriction of the cytoplasm. In plant cells, a cell plate forms between the two daughter cells, through the separation of a structure called the phragmoplast.

Structure of Eukaryotic Cells

Eukaryotic cells have a nucleus and various membrane-bound organelles.

Plasma Membrane

The plasma membrane is a thin layer that surrounds the cell. It isolates and regulates the substances that enter and leave the cell.

Core

The nucleus contains the genetic material and separates it from the cytoplasm through the nuclear envelope, a double porous membrane.

Cytoskeleton

The cytoskeleton is a network of fibers involved in cell movement and division. These fibers make up the cytoskeleton.

Centrosome

The centrosome controls the movement of the cytoskeleton fibers and intervenes in cell division.

Cell Organelles

Cell organelles are cellular elements with different functions:

• Endoplasmic reticulum: a system formed by flattened sacs and tubular channels. The rough endoplasmic reticulum has attached ribosomes, while the smooth endoplasmic reticulum lacks them.
• Golgi apparatus: formed by a set of flattened stacked cisternae. Substances from the endoplasmic reticulum accumulate and are segregated into small vesicles that are sent outside the cell.
• Ribosomes: small particles made of RNA and proteins.
• Mitochondria: spherical or elongated organelles where cellular respiration occurs.
• Lysosomes: membrane-bound vesicles that come from the Golgi apparatus. They transform complex molecules into simpler ones through hydrolysis.
• Vacuoles: membrane-bound structures whose internal vesicles accumulate different products.