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Prokaryotic Cell Structure

Bacterial Cell Structure
Bacterial Cell Anatomy and Internal Structure. Jack0m/Getty Images

Prokaryotic Cells

Prokaryotes are single-celled organisms that are the earliest and most primitive forms of life on earth. As organized in the Three Domain System, prokaryotes include bacteria and archaeans. Some prokaryotes, such as cyanobacteria, are photosynthetic organisms and are capable of photosynthesis. Many prokaryotes are extremophiles and are able to live and thrive in various types of extreme environments including hydrothermal vents, hot springs, swamps, wetlands, and the guts of humans and animals (Helicobacter pylori). Prokaryotic bacteria can be found almost anywhere. They live on your skin, in your body, and on everyday objects in your environment.

Prokaryotic Cell Structure

Prokaryotic cells are not as complex as eukaryotic cells. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell, but is coiled up in a region of the cytoplasm called the nucleoid. Prokaryotic organisms have varying cell shapes. The most common bacteria shapes are spherical, rod-shaped, and spiral.

Using bacteria as our sample prokaryote, the following structures and organelles can be found in bacterial cells:

  • Capsule - Found in some bacterial cells, this additional outer covering protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients.​
  • Cell Wall - The cell wall is an outer covering that protects the bacterial cell and gives it shape.​
  • Cytoplasm - Cytoplasm is a gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.​
  • Cell Membrane or Plasma Membrane - The cell membrane surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.​
  • Pili (Pilus singular)- Hair-like structures on the surface of the cell that attach to other bacterial cells. Shorter pili called fimbriae help bacteria attach to surfaces.​
  • Flagella - Flagella are long, whip-like protrusion that aids in cellular locomotion.​
  • Ribosomes - Ribosomes are cell structures responsible for protein production.​
  • Plasmids - Plasmids are gene carrying, circular DNA structures that are not involved in reproduction.​
  • Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA molecule.

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Binary Fission

E. coli Bacterium Binary Fission.
E. coli bacteria undergoing binary fission. The cell wall is dividing resulting in the formation of two cells. Janice Carr/CDC

Prokaryotic Cell Reproduction

Most prokaryotes reproduce asexually through a process called binary fission. During binary fission, the single DNA molecule replicates and the original cell is divided into two identical cells.

  • Binary fission begins with the single DNA molecule replicating and both copies attaching to the cell membrane.
  • Next, the cell membrane begins to grow between the two DNA molecules. Once the bacterium just about doubles its original size, the cell membrane begins to pinch inward.
  • A cell wall then forms between the two DNA molecules dividing the original cell into two identical daughter cells.

Although E.coli and other bacteria most commonly reproduce by binary fission, this mode of reproduction does not produce genetic variation within the organism. Variation is accomplished through bacterial recombination. In recombination, genes from one bacterium are incorporated into the genome of another bacterium. Bacterial recombination is accomplished by the processes of conjugation, transformation, or transduction.