Bacteria 🦠

Bacteria are unicellular organisms that do not contain a membrane bound nucleus . Each has a single chromosome present in the cytoplasm alone with an extra chromosomal DNA molecule called plasmid which is also known as vector . The plasmid can can be easily isolated from a bacterial cell and a gene can be attached with it . Thus the plasmid can carry a foreign gene into the Bacterium . In this way , plasmid acts as a carrier of a foreign gene

Introduction of genes into a bacterium

Genetic engineering is an advanced technique in biotechnology. The scientist select and isolated the useful gene from one organism and insert it into another organism , usually into a bacterium . The organism that contains a foreign gene in it's cell is called transgenic organism . The inserted gene produces the desired products in transgenic organism.

Process of introducing gene into bacterium

The process of gene introduction into the Bacterium is as under :

1) The first step is the identification and isolation of gene from donor organism

2) An enzyme called restrictions enzyme is used to cut the gene from the DNA of donor organisms

3) The isolated gene is then attached with plasmid DNA taken from a bacterium . The attached gene and plasmid DNA are collectively called recombinant DNA 🧬

4) The recombinant DNA is then introduced into a bacterium the Bacterium starts dividing and produces a bacterial colony .

Thus evening bacterium of the colony contains the desired gene and hence they produces the desired products ( protein)

Structure of bacteria a model prokaryote

Bacteria as mentioned earlier are prokaryotes. These are the smallest cellular

organisms and are the most abundant in the universe. Bacteria along with cyanobacteria (blue green algae) which are included in kingdom prokaryotae are the only livingprokaryotic organisms.

The cell wall of bacteria has murein (as mentioned earlier), it is rigid structure and determines the shape of the bacteriunm. It also protects the cells from osmotic lysis. Bacterial cell unlike eukaryotic organisms lacks discrete chromosome and uclear membrane. The nuclear material (DNA) in bacterial cells

occupies a position near to the center of the cell. This material is a single, circular

and double stranded DNAmolecule.

Bacteria only have ribosomes, composed of RNA and proteims. There are thousands of ribosomes in each healthy growing cell. Sexual reproduction in bacteria involves the exchange of DNA. This process occurs in three different ways:

Structure of bacteria

a.Capsule

Many species ofbacteria possess a tight protective covering around the cell

called capsule. It 1S a very sticky, gelatinous structure made up of polysaccharides and proteins. These bacteria are called capsulated bacteria. The capsule prevents dehydration of bacterial cell. A capsule which is less tightly bound to the cell is commonly called glycocalyx.

b, Call wall

The cell wall protects the cell and also gives it a definite shape. It is made up of peptidoglycan which is a carbohydrate-protein complex. The wall is laid in many layers and it makes the cell wall rigid. Based on the variations in the chemical constituents of cell wall, Hans Christian Gram, a Danish physician, developed a staining technique in 1884. He divided bacteria in two groups i.e. Gram-positive and Gram-negative bacteria. Gram-positive bacteria which are stained blue-purple with crystal violet dye, possess thick walls of peptidoglycan; they retain the dye when the cells are washed with an organic solvent like alcohol. Gram-negative bacteria have a thinner layer of peptidoglycan and are lose the

dye easily when rinsed with alcohol. Cell walls in Gram-negative bacteria are more

complex; the thin peptidoglycan layer is covered externally by a layer of

lipopolysaccharides. Gram-negative bacteria are more resistant than Gram-positive

bacteria because the outer layer of lipopolysaccharides impedes the entry of

the entry of antibiotics.

c. Flagella

Many species of bacteria possess thin hair-like appendages which help them in motility. Flagella are anchored in the cell wall and spin like a propeller, pulling the cell through water. A flagellum is composed of three parts i.e. a basal apparatus associated with the cytoplasmic membrane and cell wall; a short curved hook and a helical filament. The hook and the filament are made up of a protein called flagellin.

The flagella may vary in number and placement. A monotrichous bacterium possesses a single flagellum. A lophotrichous organism has a group of two or more flagella inserted at one pole of the cell. An amphitrichous bacterium is characterized by groups of flagella inserted at both end of the cell. In peritrichous bacterium

flagella are dispersed on the entire surface of the cell. Some bacteria lack flagella and are called as atrichious.

d. Pilli

Pilli are small filamentous appendages scattered all over the surface of bacterial cell. They play no part in motility. Pilli are smaller than flagella in size.They are made up of protein called pillin. Pilli help the bacteria to attach to various surfaces but in some cases they are involved in the transfer of genetic material from one to another bacterium.

e. Cell mmembrane

Cell membrane lies inner to the cell wall. It is thin, delicate, flexible and selectively permeable. Chemically it resembles the membrane of eukaryotic cells with the exception that it contains different kinds of lipids. Cell membrane inaginates into cytoplasm to torm pocket-like structure called mesosome. They help in cell division and replication of DNA.

f. Cytoplasm

Cvtoplasm lies inside the cell membrane. It is a gelatinous mass of proteins, carbohydrates, lipids, nucleic acids, salts and inorganic ions dissolved in water. It is

thick, semi-transparent and elastic and lacks membrane-bounded organelles,. The Semi fluid jelly-like portion of cytoplasm enclosed by the cell membrane is called cytosol.

g. Ribosomes

Ribosomes are RNA-protein bodies found freely dispersed within the cytoplasm. They are associated with the synthesis of proteins. They are smaller in size than the ribosomes of eukaryotic cells.

h.Genomic organization

The genome of bacteria is different from a eukaryotic genome and possesses Less DNA. It consists ofa single circular chromosome containing few-proteins than a linear chromosome of eukaryote, A membrane-bounded nucleus is missing here. The chromosome is located in a specific region of cytoplasm called nucleoid. In addition

to it's single circular chromosome, the cell also possesses extra chromosomal DNA rings of small size called plasmids. Plasmids carry a fewer genes than the normal bacterial chromosome and replicate separately independent of the normal chromosome,

Bacteria 🦠 (singular Bacterium)