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Bacterial structure

Bacteria have several essential features. These features are found in nearly all bacteria.

  • Cell wall (often made from peptidoglycan)
  • Cell membrane
  • Cytoplasm and Cytoskeleton
  • Nuclear body (nucleoid)

The nuclear body consists of a single circular chromosome, which is not enclosed in a membrane.

The chromosome typically consists of about 4000 genes. This is larger than a viral genome, but smaller than the genome of a eukaryotic cell.

Typical Gram-positive bacterial cell
Typical Gram-positive bacterial cell

In order to survive, bacteria have evolved a wide variety of structural adaptions.

These are sometimes called adaptive features because they are not universal to bacteria. Some common examples are listed below:

  • Granules are storage polymers made up of sugars and lipids which can be used as cellular energy stores.
  • Photosynthetic membranes are able to harness light energy in order to produce carbon compounds.
  • Plasmids are small circular sections of DNA that lie outside the chromosome.
Typical Gram-positive bacterial cell
Typical Gram-positive bacterial cell

Bacteria also possess structures on their outsides to assist with protection, communication and movement.

  • Capsules are made up of polysaccharide polymers and amino acids. A capsule lies outside the cell wall and membrane to protect the bacterium.
  • Pili (singular pilus) are protein filaments around $$0.5-10\text{ }\mu\text{m}$$ in length. They are located on the outside of the cell and allow cells to attach to each other and communicate.
  • Flagella (singular flagellum) are protein filaments around $$3-20\text{ }\mu\text{m}$$ long. They are present on the outside of the bacterial capsule. Flagella allow bacteria to propel themselves.
The pili are shown on the outside of the cell. This gram-positive bacterium has a flagellum.
The pili are shown on the outside of the cell. This gram-positive bacterium has a flagellum.