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Renin Angiotensin Mechanism.

Structure of Bacterial Cell

 

Introduction:

  • Size of bacterias varies between 1 to 5 microns in length, but some of them are as big as 80 microns in length.

  • They were discovered by Anton van Leeuwenhoek in 1676. They were discovered by Anton van Leeuwenhoek in 1676. 

Bacteria cell structure

  • Bacteria is a prokaryotic cell. 

  • It is enveloped by three layers like the capsule, cell wall and cell membrane. 

  • The membrane encloses protoplasm which has nuclear materials, ribosomes, food materials, etc. 

  • The cell structure is composed of,

    • Capsule

    • Cell wall

    • Cell membrane

    • Protoplasm

    • Mesosomes

    • Ribosomes

    • Nuclear material

    • Flagella and

    • Pili.

  1. Capsule: 

  • This is a mucilage sheet secreted by the cell membrane. 

  • It is a slimy layer which is loosely arranged around the cell wall. 

  • This is present only in some bacteria during the adverse environmental conditions. 

  • It protects the cell from desiccation in conditions like high temperature and drought. 

  • This capsule is digested and consumed by the bacteria when the conditions get normal.

  1. 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 muropeptides. 

  • This character of bacteria is similar to plant cells having a cell wall. 

  • The muco-polypeptide (Peptidoglycan)  is a polymer of N-Acetyl muramic acid (NAM) and N-acetylglucosamine (NAG). 

  • Unlike the plants, bacterial cell walls lack cellulose in it.

  • This cell wall chemistry varies significantly and bacteria are differentiated as Gram-positive and gram-negative strains.

  • The gram +ve bacteria have a thick wall made of single layers of mucopeptide.

  • On the other side, the Gram -ve have three layers like lipoprotein, lipopolysaccharide and mucopeptide.

  1. 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 hence it is semipermeable.

  •  It regulates the movement of substances into and out of the cell.

  • Interestingly, it has numerous respiratory enzymes in it. 

  • The ATP is formed by oxidative phosphorylation here with some of the TCA cycle enzymes present in the protoplasm. 

  • The lack of mitochondria in the cell is substituted by this cell membrane.

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

  1. 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, endoplasmic reticulum are absent in it.

  1. Mesosomes:

  • These are spherical invaginations formed by the infoldings of the cell membrane.

  • They are found to be involved in the replication of genetic material and cell division. 

  • Further, they are involved in the formation of cell walls and excretion of exo-enzymes.

  1. Ribosomes:

  • The bacterial cell structure has 70 s ribosomes. 

  • It consists of two subunits as the 50S and 30S ribosomes.

  • The ribosomes are present in free-flowing form and are grouped into polysomes.

  • These ribosomes are useful in protein synthesis. But, for humans, they are the target of an antibiotic action in the treatment of bacterial infections.

  1. Nuclear material:

  • Bacteria lack a true nucleus; the genetic material is not enclosed by a nuclear membrane. 

  • The nuclear material consists of a single circular chromosome. 

  • The  DNA is present as a single-stranded circular molecule. 

  • Additional rings of DNA called plasmid are present in the cytoplasm. 

  • These plasmids are exchanged in between bacteria during sexual reproduction.

  • Plasmids contain genes essential for survival viz. Antibiotic resistance. 

  1. Flagella: 

  • These are the organs of locomotion present in motile bacteria. 

  • This is a hair or whip-like structure arising out of basal granule.

  • 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.

  1. Pili: 

  • These are also called as 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 also consists of food stored as glycogen, proteins and oil drops. 

  • Further, the photosynthetic bacteria have green pigment distributed in protoplasm lamellae.

  • Pili are antigenic.
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