Just beneath the cell wall is the cell membrane or plasma membrane. It is very thin. Flexible and completely surrounds the cytoplasm. Plasma membrane is very delicate in nature any damage to it results in death of the organism. Bacterial membranes differ from eukaryotic membranes in lacking sterols such as cholesterol.
Cell membrane regulates the transport of proteins, nutrients, sugar and electrons or other metabolites. The plasma membranes of bacteria also contain enzymes for respiratory metabolism.
The cytoplasm of prokaryotic cell lacks membrane bound organelles and cytosketeton (microtubutes). The cytoplasmic matrix is the substance present between the plasma membrance and the nucleoid. It has gel like consistency. Small molecules can move through it rapidly. The plasma membrane and every thing present within it is known as protoplast. Thus the cytoplasmic matrix is a major part of protoplast. Other large discrete structures such as chromatin/nuclear body, ribosomes, mesosomes and granules and nucleoid are present in this matrix.
A bacterial cell unlike the cells of eukaryotic organisms lacks discrete chromosomes and nuclear membrane. The nuclear material or DNA in bacterial cells occupies a position near to the center of cell. This material is a single, circular and double stranded DNA molecule. It aggregates as an irregular shaped dense area called the nucleoid. This chromatin body is actually an extremely long molecule of DNA that is tightly folded so as to fit inside the cell component. Since bacteria have a single chromosome, they are haploid.
“other names for nucleoid are nuclear body, chromatin body and nuclear region.
It is visible in the light microscope after staining with Feulgen stain.
Escherichi coli closed circle chromosome measures approximately 1,4000um”
Many bacteria contain plasmids in addition to chromosomes. These are the circular, double stranded DNA molecules. They are self-replicating and are not essential for bacterial growth and metabolism. They often contain drug resistant, heavy metals, disease and insect resistant genes on them.
“plasmids are important vectors, in modern genetic engineering techniques”.
Ribosomes are composed of RNA and proteins. Some may also be loosely attached to plasma membranes. They are protein factories. There are throusands of ribosomes in each healthy growing cell. They are smaller than eukaryotic ribosomes.
The cell membrane, invaginates into the cytoplasm forming structure called as mesosome. Mesosomes are in the form of vesicles, tubules or lamellae. Mesosomes are involved in DNA replication and cell division where as some mesosomes are also involved in export of exocellualar enzyme.
Granules and storage bodies
Since bacteria exist in a very competitive environment where nutrients are usually in short supply. They tend to store extra nutrients when possible. These may be glycogen, sulphur, fat and phosphate. In addition, cells contain waste materials that are subsequently excreted. For example, common waste materials are alcohol, lactic acid and acetic acid.
Certain species of bacteria produce spores, either external to the vegetative cells (exospores) or within the vegetative cells (endospores). They are metabolically dormant bodies and are produced at a late stage of cell growth. Spores are resistant to adverse physical environmental conditions such as light, high temperature, desiccation, PH and chemical agents. Under favorable conditions they germinate and form vegetative cells.
Cysts are dormant, thick-walled, desiccation resistant forms and develop during differentiation of vegetative cells which can germinate under suitable condition. They are not heat resistant.