Write a note on the structure of bacterial cells.


Structure of bacteria:

  • Have cell wall surrounding the cell membrane

  • Absence of a well-defined nucleus

  • May have plasmids − small, circular, extra-chromosomal DNAs present in addition to the genomic DNAs; this confers characteristics like antibiotic resistance to bacteria, and help in transformation.

  • Cell Envelope − Three-Layered Structure

    • Glycocalyx (Outermost): May be present in the form of loose sheath called slime layer in some bacteria, or as a thick and tough capsule in others

    • Cell wall (middle): Determines the shape of a cell and provides a strong structural support

    • Plasma Membrane (innermost): Semi-permeable and structurally similar to that of eukaryotic cells.

  • Mesosome 

    • Formed by the extension of the plasma membrane into the cell

    • These extensions are made up of vesicles, tubules and lamellae.

    • Functions: Cell wall formation; DNA replication and distribution; respiration and secretion processes; increase surface area of plasma membrane and enzymatic content

  • Bacteria may be − Motile or Non-Motile

    • Motile: Have flagella

    • Non-motile: Lack flagella

  • Flagella has three parts: Filament, Hook, Basal body

  • Pili (tubular structures made of proteins) and fimbriae (bristle-like fibres) are also present along with flagella, but their function is attachment (to the substratum or the host cell).

  • Depending upon the cell envelope, bacteria are of two types:

    • Gram positive − take up gram stain

    • Gram negative − do not take up gram stain


  • Associated with plasma membrane

  • Made up of two subunits: 50S and 30 S = 70S

  • Site of protein synthesis

  • Polysome: When several ribosomes attach to a single mRNA

  • Help in the translation of mRNA into proteins

Inclusion Bodies

  • Reserve material in bacterial cell is stored in the form of inclusion bodies.


  • 1
Structure of bacteria:

Cell Wall:
Cell walls of bacteria are made up of glycoprotein murein.
The main function of cell wall is it helps in providing support, mechanical strength and rigidity to cell.
It protects cell from bursting in a hypotonic medium.

Plasma Membrane:
It is also known as cytoplasmic membrane (or) cell membrane.
It is composed of phospholipids, proteins and carbohydrates, forming a fluid-mosaic.
It helps in transportation of substances including removal of wastes from the body.
It helps in providing a mechanical barrier to the cell.
Plasma membrane acts as a semi permeable membrane, which allows only selected material to move inside and outside of the cell.

Helps in cellular growth, metabolism and replication.
Cytoplasm is the store houses of all the chemicals and components that are used to sustain the life of a bacterium.

A tiny granule made up of RNA and proteins.
They are the site of protein synthesis.
They are freely floating structures that helps in transferring the genetic code.

Plasmids are small circle of DNA.
Bacterial cells have many plasmids.
Plasmids are used to exchange DNA between the bacterial cells.

This is a rigid rotating tail.
It helps the cell to move in clockwise and anticlockwise, forward and also helps the cell to spin.
The rotation is powered by H+ gradient across the cell membrane.

Short protein appendages.
Smaller than flagella.
Fixes bacteria to surfaces.
It also helps in reproduction during conjugation.

Capsule is a kind of slime layer, which covers the outside of the cell wall.
They are composed of a thick polysaccharide.
It is used to stick cells together and works as a food reserve.
It protects the cell from dryness and from chemicals.
  • 2
What are you looking for?