Cells are structural and functional units of an organism. That means the cell is the main constituent as well as the smallest unit that performs the life activity of an organism.
Although very small in size, each cell in the body has a specific task for the survival of an organism. There are two types of cell structures that exist on this earth.
Prokaryotic Cells Definition
Prokaryotic cells are cells that do not have a nucleus (the nucleus of a cell encased in a membrane). In some prokaryotic literature, it is also defined as a cell that does not have an organnel encased in membranes. Prokaryotic cells are the constituent cells of several types of organisms, namely all types of single-celled organisms, Archaea domains and Bacteria domains.
Prokaryotic cell parts and their functions
Pili or pilus is a fine hair-shaped structure that protrudes from the cell walls. The Pili is composed of proteins and it is found in many gram-negative bacteria. The pili is similar to flagellum (flagella) but it is shorter, stiffer, smaller in diameter, and much more in number.
The function of pili is as a place of entry of genetic material during mating and helps attach itself to animal or plant tissues. Pili is not a tool of motion. There are also fimbriae that are similar to pili but shorter.
Plasmids are DNA ekstrachromosomal smaller than chromosomes and circular in shape. DNA on the plasmids is capable of being replicated on its own. The number and size of plasmids in cells varies depending on the type of plasmid they have.
Plasmid function is to carry the non-essential properties of DNA that give prokaryotic cells, such as antibiotic resistance, virulence (the ability to cause disease), and conjugation (sharing plasmids with other prokaryotic cells).
Nonessential means it does not play a direct role in metabolism and any biological activity that supports bacteria. Plasmids are also found in some eukaryotic microbes such as yeast.
Ribosomes are nano-machines for protein synthesis. Prokaryotic cells have a lot of ribosomes. The function of ribosomes is to translate in the synthesis of proteins that convert the genetic code of DNA into proteins.
There are several differences between prokaryotic ribosomes and eukaryotic ribosomes. Smaller prokaryotic ribosomes and less rRNA.
Cytoplasm is a fluid of cells in a cell membrane composed of water, proteins, lipids, minerals, and enzymes. The organnel is also in the cytoplasm. Cytoplasmic function is as the place where metabolic reactions take place and store food reserves in the form of insoluble granules (storage granules).
Plasma membranes are thin semi-permeable biological membranes consisting of two layers of phospholipids and embedded with proteins. The function of plasma membranes is as a cell protector against extracellular environments and regulates the traffic of substances in and out of cells.
Cell walls are the outer coating structure of the harder and stiffer cells that are between the capsules and the plasma membrane. There are pores for the entry and exit of molecules. The function of the cell wall is to shape and protect the internal organelles of the cell.
Capsules are the outermost layers of bacteria of varying thickness in each type of bacteria. The thick layer is called a capsule composed of glycoproteins and it is usually found in disease-carrying bacteria (pathogenic).
While the thin layer is called a layer of mucus composed of water and polysaccharides and it is usually found in saprobic bacteria (getting food from the rest of the organism).
The function of the capsule is as a cell protector, preventing cell dryness, helping to attach itself to other bacteria or in other organisms, and protecting pathogenic bacteria from the influence of host cell antibodies.
Flagella is a whip-like structure that allows cells to move. In prokaryotes, the structure of flagella is very simple compared to eukaryotic cells because it consists only of a single fiber of flagellin protein. The flagella function is as a cell motion tool. Prokaryotic flagella movements are like twirling.
A nucleoid is a thin, transparent region of cells that contains primary DNA. Nucleoids are the main centers of DNA transcription and replication. Its irregular shape with nucleoid size varies depending on the cell type. DNA strands on nucleoids are circular or oval in shape.
Nucleoid function is similar to the nucleus of a cell (nucleus) in eukaryotic, only without a nucleus membrane so that it comes into direct contact with the cytoplasm.