A cell is a functional, structural and biological unit of all living organisms. It is also an autonomous, self-replicating unit that can exist as either a sub-unit in a multi-cellular organism (such as an animal or plant) or as an independent unit (such as a unicellular organism), and carry out certain functions, according to Biology Online. Furthermore, a cell is also a membrane-bound structure that contains particular bio-molecules such as proteins, polysaccharides and nucleic acids.
Cells are usually divided into two categories, prokaryotic (those lacking a cell nucleus) and eukaryotic (those bound by a membrane). However, they do have certain features in common, according to PhSchool. The four common features that they share include a plasma membrane, cytoplasm, DNA and ribosomes.
A plasma membrane is a phospholipid bilayer made up of proteins that separate the cell from its surroundings. It functions as a barrier for importing and exporting certain materials, according to PhSchool. The cytoplasm is referred to as all of the material contained within the plasma membrane but excluding the nucleus. It consists of the cytosol (fluid) and organelles. The cell's DNA is its genetic material. It is located in a non-membrane-bound nucleoid region within the prokaryotic cells and in the membrane-bound nucleus within the eukaryotic cells. Ribosomes are organelles within which protein synthesis takes place.
Prokaryotic cells, or prokaryotes, are simple cell organisms such as bacteria. The main difference between prokaryotes and eukaryotes is that they lack membranous organelles and a nucleus, according to PhSchool. The membrane of eukaryotic cells contains certain organelles, like mitochondria.
The organelles bound by membrane within eukaryotes include nuclear envelope, lysosomes, the Golgi apparatus and mitochondria. The nuclear envelope is a double-layered membrane that encloses the nucleus and separates it from the cytoplasm, according to Biology Online. Lysosomes are organelles that contain a variety of enzymes that are used primarily for digestion. The Golgi apparatus' primary function is to process and package proteins. According to Cells Alive, mitochondria provide the cells with energy to divide, move, produce secretory products and contract.
The nuclear envelope is composed of a lipid bilayer and made up of nuclear pores (holes) that regulate the exchange of different materials such as RNA and proteins, according to Biology Online. The specific function of lysosomes include digestion of macromolecules from autophagy, endocytosis, phagosytosis, repair of damage of the plasma membrane, and apoptosis.