Component of Bacterial Cell
A bacterial cell is made of a cell envelope, cytopalsm nucleoid, plasmid, inclustion bodies, pilli and fimbriae
A- Cell Envelope - It is covering over protoplast of a bacterial cell. Cell envelop has three part - 1- Mucilage 2- cell wal 3- palsmalema
1-
Mucilage sheath (Glycocalyx) - On the out side cell is coverd by mucilage of non cellulosic polysccherides.Thick layer of Mucilage (more than 0.2µm) is called cpsule. A loos sheath of mucilage called slime layer. Mucilage protect the cell against desiccation, toxins, phagocytes, and viruses. Mucilage also possesses ion exchange capacity in the inner layer.
2-
Cell Wall - Cell wall is elastic porous and freely permeable to solutes less than 10,000 daltons. Cell wall of G+ Bacteia is smooth and wavy in Gram - Bacteria. The Cell wall contain peptidoglycan, diaaminopimelic acid, lipid and protein. Peptidoglycan forms several layers in the wall of Gram +ve Bacteria and a single layer in the wall of Gram -ve bacteriya, Gram + Bact. cell wall has N-Acetyl Glucosamine (NAG) and N-Acetyl Muremic (NAM) Acid.
The wall of Gram +ve Bacteria contain theoic acid, which act as recepter sites and surface antigen. the inner wall layer of Gram (-) Bacteria has peptidoglycan while the outer one has lipopolysacherides, proteins and phopsholipids. Periplsmic space occurs between plsma membrane and cell wall.
3-
Plasmalema (Plasma membren) - It is thin selectively permeable membrane which forms the innermost component of cell envelop and outer covering of cytoplasm. palsma membrane has typical lipoprotein structure as visualised by fluid mosaic model. There is as lipid bilayer. The lipid bilare is stabilised by other pentacyclic sterols called hapanoids instead of cholesterol.
Plasma membrane holds semifluid cytopalsmic content, separates them from surroundings serves as seletively peremeable barrier and having receptor molecules for detection and responding to chemicals in the surroundings. It contains Enzymes for respiration lipid synthesis, cell wall constituents and photosynthesis. Some riboseomes are also attched to it. Mesosome is an extension of plasmalemma.
B- Cytoplasm - It ia granular crystallo - colloidal complex that fills the cell protoplast but excludes nucleoid. It has numerus organels in it-
1- Mesosomes - A complex multilaminated membranous structure called mesosome is formed by ivagination of plasma membrane. It is of tho type - Septal and Lateral. Septal mesosome in in contact with nuceoid. It take part in separation of replicated nucleoinds and septum formation. Lateral or peripheral mesosome is not conncted with nucleoid. It is equivalent to mitochondrion and is called chondrioid. Respiratory enzymes occur over it as well as the plasma membrane.
2- Ribosomes - They are 70S. Each ribosome has two subunits, 50S and 30S. Ribosome take part in protein synthesis. 4-8 ribosomes are often found attached to a single mRNA strand for formong copies of the same polypeptide. Ribosome aggregates are called polysomes or polyribosomes. Bacteria have two types of 70S ribosomes Fixed (aattache to palsma membrane ) and Free (matrix Ribosome). Fixd ribosome protiens form trasport to outside.
3- Chrometophores - the are pigment containnig complex of photoototrophic bacteria and cynobacteria. In cynobacteria (BGA) thylecoid occur in the outer part of cytoplasm called chromoplasm. They bear chlorophill a and carotinoid. Attached to thilecoids are minute granuls clled phycobilisome. The posses phycobilins. In green Bacteria Phtosynthetic pigments lie insid chrometophores calle chlosrosomes.
C- Nucleoid -DNA ) - It is folded singal cercular strand of DNA double helix which is also called genophore. prochromosomes or chromonema. DNA strand dis 250- 700 times the length of the cell. It is folded in a super coiled manner. with the help of non-histone protein or polyanines and RNA. Procaryotic DNA is called naked due to its non association with histone proteins and absence of nuclear envelope. Nucleoid lies directly inside the cytoplasm. It is however not free. Nucleoid is in contect with cell membrane ither directly or through mesosomes.
D- Plasmid - The additional or extra chromosomal small rings of DNA having a few useful but not vital genes. e.g. F-Factor (Fertility Factor), Nif -Factor (Nitrogen fixing Gene) R-Facter (resistance Facter).AT times Plasmid associate temporarily with nucleoid. They are called apiosomes. Plsmid have these days become an importent tool in genetic engineerring as vectors of genes.
E- Inclution Bodies - They are non living structures present inside the cytoplasm.
1- Gas Vacuoles - The occur in cynobacteria, purpal bacteria, green bacteria and afew other planktonic bacteria. A gas vocule is made up of a large number of minute hexagonal, hollow and cylindrical gas vesicals each surrounded by a ribbed non-lipid protein membrane. The protein membrane is permeable to atmospheric gases but impermiable to water.
2- Inorganic Inclusions- Granules) Granules of inorganic substance occure in many bacteria e.g. volutin granules sulpher granules, iron granules, megnatic granules. These granules are also called metachromatic granuls becaause of their ability to pick up differnt colours with basic dyes
3- Food Reserve- Cynobacteria posses three types of food reserve - α granules, β-granules, and proteins. Commen food reserve of bacteria is glycosen. Natural fats are absent. Instead many bacteria posses
poly β hydroxybutyrate or PHB granules. A biodigradeble plastics can be prepared from them. Proeins occure as protein granules.
F- Flagila - They occur in some bacteria. bacterial flagilla are unistranded equivalent to a single microtubular fiber. Diameter is about 20nm. Baterial flegillum has three parts - Basal Body, Hook and filament. Basal Body is Rod Like Basal part of flegillum which occurs in cell envelop and is attachet to it by means of two pairs of rings in gram -ve bacteria and only one pair of rings in gram +ve bacteria. Hook is curved and thickest part. It is made up of protein units different from those of filament. Filament is long tubuler structure of flagillum. Its wall is formed of 3-5 spiral rows of globular protein molecules called flagillin. Bacterial flagillum rotates by 360 digree that brings about bacword pushing of water.
G- Pili - They are 1-4 long holow tubes which are also called sex pili or F pilli because the take part in conjugation. Pili develop in Gram -ve bacteria Similar structures present in Gram +ve bacteria called Spinae. Pili are made of a distinct proteint calle pilin.
H- Fimbriare- The are numerious, small fibors outgrowths from the cell surface which reach a length of 0.1-1.5 μ m. Fimbriae help in attching bacteria to solid surface.
