Parts, Functions & Diagrams of Prokaryotes
CLASS NOTES from Science Prof Online
Prokaryotes are single-cell organisms, including bacteria and their bacteria-like cousins Archaea. Prokaryotic cells are much simpler than the more evolutionarily advanced eukaryotic cell. Whereas eukaryotic cells have many different functional compartments, divided by membranes, prokaryotes only have one membrane, the plasma membrane, which encloses all of the cell’s internal contents. If a eukaryotic cell is analogous to a big house with many different rooms, a prokaryotic cell is like a one-room, studio apartment.
Article Summary: Prokaryotes - simple, single-cells, yet remarkably successful organisms. Here's an overview of the structures and functions of prokaryotic cells.
Prokaryotic Cell Structures, Functions & Diagrams
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Genetic Material of Prokaryotes
- Nucleoid: The nucleoid is the region of the prokaryotic cytoplasm that contains the genome—the main genetic material (DNA) of the cell. Bacteria and Archaeans typically have a single, circular chromosome.
- Plasmids: In addition to the bacterial chromosome, bacteria may also contain one or more plasmids. A plasmid is a non-essential piece of DNA that confers an advantage to the bacteria, such as antibiotic resistance, virulence (the ability to cause disease) and conjugation (a bacterium’s ability to share its plasmids with other bacteria). Plasmids are also found in some eukaryotic microbes, such as yeasts.
Prokaryotic Cell Structures Outside of Plasma Membrane
- Cell Wall: Nearly all prokaryotes have a protective cell wall that prevents them from bursting in a hypotonic environment (an aqueous environment with a lower concentration of solutes than are found within the cell). The composition of cell walls vary depending on the type of organisms, but most cell walls contain a combination of the major organic molecules—proteins, carbohydrates and lipids. Bacteria have a unique molecule called peptidoglycan in their cell wall. Archaean cell walls do not contain this molecule. Cell wall composition of bacteria allow scientists to classify them as either Gram-positive or Gram-negative.
- Glycocalyx: The glycocalyx is a layer present in some bacteria, and located outside of the cell wall. There are two types of glycocalyces: slime layers and capsules. Slime layers help bacteria stick to things and protect them from drying out, particularly in hypertonic environments. Capsules also allow bacteria to stick to things, but have the added benefit of helping encapsulated bacteria hide from the hosts immune system.
- Cell Extensions: There are several different types of cell extensions associated with bacteria, all a made of delicate protein strands. Bacterial cell extensions include:
- flagella: long whip-like extensions that help bacteria move about the environment
- fimbriae: allow bacteria to adhere to target host cells, so play a major role in
- conjugation pili: the tubes used to transfer plasmids from donor to recipient
Sources & Helpful Links on Biological Cells
- Bauman, R. (2014) Microbiology with Diseases by Taxonomy 4th ed., Pearson Benjamin Cummings.
- Park Talaro, K. (2008) Foundations in Microbiology, McGraw-Hill.
- Becker, W. M. et. al. (2009) The World of the Cell. Pearson Benjamin Cummings.
- Campbell, N. & Reece. J. (2002) Biology, Sixth Edition. Benjamin Cummings.
Page last updated: 7/2014
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Here is a list and description of the main cellular components of prokaryotes. A labeled diagrams of a prokaryotic cell and a related assignment appear below.
Internal Structures of Prokaryotic Cells
- Plasma Membrane: The plasma membrane is a double-layer of phospholipids with associated proteins and other molecules. It is essentially the “bag” that holds all of the intracellular material and regulates the movement of materials into and out of the cell.
- Cytoplasm: This is the gel-like fluid that the cell is filled with, inside the plasma membrane--liquid with all of the cellular organelles suspended within.
- Cytoskeleton: It's only recently been discovered that rod-shaped bacteria and Archaea possess cytoskeletal proteins that function in a similar way to the cytoskeleton of eukaryotic cells. This scaffolding provides structural support to the cell and plays a role in cell-division.
- Ribosomes: All cells, both prokaryotic and eukaryotic, have multiple ribosomes within. Ribosomes are the protein-making machinery of the cell.