Bacteria Structure with Diagram and Functions

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Bacteria structure is unicellular and microscopic with diverse shapes.

The size, in general, ranges between 1 to 5 microns in length, but some are as big as 80 microns in length.

Cell Structure of Bacteria

Bacteria is a prokaryotic cell and typically consists of 3 major components, like

  • Cell wall and membrane
  • Protoplasm
  • Chromosome and other cell organelles.

The outermost cover of the bacterial cell consists of three layers, like

The membrane encloses protoplasm and chromosomes along with materials, ribosomes, food materials, etc.

Bacteria structure
The bacteria cell structure shows polyribosomes, cell walls, capsules, Pili, protoplasm, mesosomes, chromosomes, cell membranes, and flagella.

The cell structure is composed of

  1. Capsule
  2. Cell wall
  3. Cell membrane
  4. Protoplasm
  5. Mesosomes
  6. Ribosomes
  7. Nuclear material
  8. Flagella and
  9. Pili.

Capsule

  • It is a slimy layer that is loosely arranged around the cell wall.
  • This is present only in some bacteria during adverse environmental conditions.
  • This sheet is secreted by the cell membrane and comprises polysaccharides or polypeptides.
  • It protects the cell from desiccation in conditions like high temperatures and drought.
  • The bacteria digests and consumes this capsule when the conditions get normal.

Cell wall

  • It is a hard envelope present around the bacterial cell. It gives definite shape and protection to the entire cell.
  • The cell wall is a nonliving cover made up of mucopolysaccharides and mucopeptides.
  • This character of bacteria is similar to plant cells having a cell wall.
  • The muco-polypeptide is a polymer of N-acetyl muramic acid (NAM) and N-acetylglucosamine (NAG). Unlike plants, bacterial cell walls lack cellulose.
  • This cell wall chemistry varies significantly, differentiating bacteria as Gram-positive and Gram-negative strains.
  • The gram-positive bacteria have a thick wall made of single layers of mucopeptide.
  • Conversely, the Gram-negative bacteria has three layers: lipoprotein, lipopolysaccharide, and mucopeptide.

Cell membrane

  • This is the outermost cell organelle lying immediately below the cell wall.
  • It is a living membrane. This cell membrane forms an external lining layer to the protoplasm.
  • It is made of phospholipids and proteins and is semipermeable.
  • It regulates the movement of substances into and out of the cell.
  • Interestingly, it has numerous respiratory enzymes.
  • The ATP is formed by oxidative phosphorylation here due to the presence of the TCA cycle enzymes present in the protoplasm.

So, the cell membrane is useful for the transport of substances and also respiration.

Protoplasm

  • It is a viscous mixture present inside the cell membrane.
  • It consists of carbohydrates, lipids, proteins, water, minerals, glycogen, etc.
  • Most cell organelles of higher organisms like the mitochondria, Golgi complex, plastids, and endoplasmic reticulum are absent in it.

Mesosomes

  • These are spherical invaginations formed by the infoldings of the cell membrane.
  • Further, they are involved in the formation of cell walls and the excretion of exo-enzymes.

Ribosomes

  • The bacterial cell structure has 70 s ribosomes. It consists of two sub-units, the 50S and 30S ribosomes.
  • The ribosomes present in the free-flowing form are grouped into polysomes.
  • These ribosomes are useful in protein synthesis. However, humans are the target of an antibiotic attack in treating bacterial infections.

Nuclear material

  • As mentioned before, bacteria lack a true nucleus. A nuclear membrane does not enclose the genetic material.
  • The DNA is present in a single-stranded circular molecule. Additional rings of DNA called plasmids are present in the cytoplasm.

Flagella

  • These are the organs of locomotion present in motile bacteria.
  • This is a hair or whip-like structure arising out of basal granules.
  • They are made up of protein flagellin, which is arranged in eight parallel chains.
  • A bacteria cell can consist of single, double, or multiple flagella.

Atrichous = no flagella, Monotrichous= Single flagella, lophotrichous= flagella at one side, amphi trichous= Flagella as tuft on two sides, peritrochous=flagella all around the cell.

Pili

  • These are also called fimbriae and are small tubular outgrowths present in Gram-negative bacteria.
  • They are helpful in attachment to another bacterial cell during sexual reproduction by conjugation.
  • Besides the above, bacteria structure consists of food stored as glycogen, proteins, and oil drops.
  • Further, the photosynthetic bacteria have green pigment distributed in protoplasm lamellae.

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