A bacterial cell consists of a cell envelop, cytoplasm, nucleoid, plasmids, inclusion bodies, flagella, pili and fimbriae.
Cell envelop :- It is the outer covering of protoplasm of bacterial cell. Cell envelop consists of three components- glycocalyx, cell wall, cell membrane.
Glycocalyx :- ( Mucilage sheath) It is the outermost mucilage layer of the cell envelop occurs in the form of loose sheath also called slime layer. It has several secondary functions:- a) Prevention of desiccation. b) Protection from phagocytes. c) Protection from toxic chemicals and drugs. e) Attachment. f) Immunogenicity.
Cell Wall :- The cell wall is a rigid and made up of heteropolymer mucopeptide complex containing N-acetyl glucose amine and N-acetyl muramic acid and peptidoglycans. They are cross linked by small peptides chains. Lysozyme the antibacterial enzyme of tears, saliva, gastric juices etc. has the ability to hydrolyse the peptidoglycan.
Plasma Membrane:- It is selectively permeable membrane that forms the inner most layer of the cell envelop. Bacterial plasma membrane has a structure similar to typical membrane. It is made up of phospholipids and proteins and some polysaccharides .
Cytoplasm:- It is a colourless, semi-fluid material which is composed of proteins, lipids, carbohydrates, water and minerals salts. Membrane bound cell organelles as found in eukaryotes are absent. Cytoplasmic streaming is absent. Sap vacuoles are absent. Various structures are found in cytoplasm are as follows;-
i) Mesosome:- The membrane is inverted at certain places in the cytoplasm. These invaginations are known as mesosome. Mesosome are of two types- septal and lateral. Septal mesosome connects nucleoid with plasma membrane and helps in the cell division. Lateral mesosome are not connected with nucleoid. It contains respiratory enzymes therefor , also called chondrioid.
ii) Ribosomes:- They are small membraneless, submicroscopic ribonucleoprotein structures. The ribosomes are 70S in nature ( S denotes sedimentation coefficient or Svedberg number). Each ribosomes has two subunits, larger 50S and smaller 30S. Ribosomes are of two types. Fixed and free. Ribosomes generally occur in helical groups called polysomes and polyribosomes.
iii) Chromatophores:- They are internal membrane systems present in photosynthetic prokaryotes. Chromatophores develop as membrane lined sacs or thylakoids.
iv) Nucleoid;- It represents the genetic material of prokaryotes. It is also known as the prochromosome, genophore and chromoneme. Nucleoid consists of a single circular strand of DNA duplex. DNA is naked because of its non-association with histone proteins. Nuclear membrane is absent and nucleoid is embedded freely in the cytoplasm. It is equivalent to the single chromosome of eukaryotes.
v) Plasmids:- They are self replicating, extra chromosomal segments of double stranded, circular, naked DNA. They are independent of main nucleoid. Some of them contains important genes like fertility factor, nif genes and resistant factor. Plasmids which can get associated temporarily with nucleoid are known as episomes.
vi) Inclusion bodies:- They are non-living structures present in the cytoplasm. These are gas vacuoles, inorganic inclusions and food reserve. Gas vacuoles are gas storing vacuoles found in cyanobacteria, purple and green bacteria. Inorganic inclusions are sulphur granules, iron granules and magnetite granules. Food reserv are cyanophycean starch, lipid globules and protein granules.
vii) Flagella:- A bacterium flagellum is a long whip like structure projecting on the surface. It is formed of single fibril. It arises from a basal plate situated just inside the plasma membrane. The flagella helps in locomotion. The flagella is made up of flagellin protein.
viii) Pili:- These are small, non-motile hair like structures present on the surface of some forms of bacreia. They help in attachment of bacterial cell, and play important role in bacterial conjugation.
i) Mesosome:- The membrane is inverted at certain places in the cytoplasm. These invaginations are known as mesosome. Mesosome are of two types- septal and lateral. Septal mesosome connects nucleoid with plasma membrane and helps in the cell division. Lateral mesosome are not connected with nucleoid. It contains respiratory enzymes therefor , also called chondrioid.
ii) Ribosomes:- They are small membraneless, submicroscopic ribonucleoprotein structures. The ribosomes are 70S in nature ( S denotes sedimentation coefficient or Svedberg number). Each ribosomes has two subunits, larger 50S and smaller 30S. Ribosomes are of two types. Fixed and free. Ribosomes generally occur in helical groups called polysomes and polyribosomes.
iii) Chromatophores:- They are internal membrane systems present in photosynthetic prokaryotes. Chromatophores develop as membrane lined sacs or thylakoids.
iv) Nucleoid;- It represents the genetic material of prokaryotes. It is also known as the prochromosome, genophore and chromoneme. Nucleoid consists of a single circular strand of DNA duplex. DNA is naked because of its non-association with histone proteins. Nuclear membrane is absent and nucleoid is embedded freely in the cytoplasm. It is equivalent to the single chromosome of eukaryotes.
v) Plasmids:- They are self replicating, extra chromosomal segments of double stranded, circular, naked DNA. They are independent of main nucleoid. Some of them contains important genes like fertility factor, nif genes and resistant factor. Plasmids which can get associated temporarily with nucleoid are known as episomes.
vi) Inclusion bodies:- They are non-living structures present in the cytoplasm. These are gas vacuoles, inorganic inclusions and food reserve. Gas vacuoles are gas storing vacuoles found in cyanobacteria, purple and green bacteria. Inorganic inclusions are sulphur granules, iron granules and magnetite granules. Food reserv are cyanophycean starch, lipid globules and protein granules.
vii) Flagella:- A bacterium flagellum is a long whip like structure projecting on the surface. It is formed of single fibril. It arises from a basal plate situated just inside the plasma membrane. The flagella helps in locomotion. The flagella is made up of flagellin protein.
viii) Pili:- These are small, non-motile hair like structures present on the surface of some forms of bacreia. They help in attachment of bacterial cell, and play important role in bacterial conjugation.
Are mesosomes real or are they artifacts from EM prep techniques?
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