Cells that lack a membrane-bound nucleus are called prokaryotes (from the Greek meaning before nuclei). These cells have few internal structures that are distinguishable under a microscope.
Cell Wall: Made of a murein (not cellulose), which is a glycoprotein or peptidoglycan (i.e. a protein/carbohydrate complex). It’s the outer covering of most cells that protects the bacterial cell and gives it shape.
Plasma membrane: Controls the entry and exit of substances, pumping some of them in by active transport.
Cytoplasm: Contains all the enzymes needed for all metabolic reactions, since there are no organelles.
Ribosome: The smaller cell structures all free in the cytoplasm meaning attached to membranes. They are used in protein synthesis which is part of gene expression.
Nucleoid: Is the region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. DNA is always a closed loop (i.e. a circular), and not associated with any proteins to form chromatin.
Flagella: These long thread-like attachments are generally considered to be for movement. They have an internal protein structure that allows the flagella to be actively moved as a form of propulsion.
Pilli: Hair-like structures on the surface of the cell that attach to other bacterial cells. Shorter pili called fimbriae help bacteria attach to surfaces. They are associated with different types of attachment. In some cases they are involved in the transfer of DNA in a process called conjugation or alternatively as a means of preventing phagocytosis (being engulfed by another cell)
Cell Capsule: it’s a thick polysaccharide layer outside of the cell wall. Used for sticking cells together, as a food reserve, as protection against desiccation and chemicals, and as protection against phagocytosis. In some species the capsules of many cells in a colony fuse together forming a mass of sticky cells called a biofilm. Dental plaque is an example of a biofilm.