Types of Cells

Types of Cells

There are two types of cells: Eukaryotic and Prokaryotic.

Prokaryotic Cells

The word prokaryote comes from the Greek pro- (before) and karyon (nut or kernel referring to cell nucleus). The prokaryotes are a group of organisms that lack a cell nucleus or any other membrane bound organelle. Most prokaryotes are unicellular but a few like Myxobacteria have multicellular stages in its life cycle.

A prokaryotic cell consists of:

• flagella and pilli, that project out from the cell's surface. These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells;
• enclosing the cell is the cell envelop - generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter.
• inside the cell is the cytoplasm that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. A prokaryotic chromosome is usually a circular molecule. Though not forming a nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extra chromosomal DNA elements called Plasmids, which are usually circular. Plasmids enable additional functions such as antibiotic resistance.

Eukaryotic Cell

The word eukaryote comes from Greek eu- (true) and karyon (nut or kenel). A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus. Most eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus.