Prokaryotic Cell Structure and Function of Organelles

In this Prokaryotic cell structure and function of organelles post we have briefly explained about characteristics, morphological types, a component of prokaryotic cells and reproduction.

Prokaryotic Cell Structure and Function of Organelles

Prokaryote means before nucleus in Greek. They include all cells which lack nucleus and other membrane bound organelles. Mycoplasma, virus, bacteria and cyanobacteria or blue-green algae are prokaryotes. Bacteria are example of the prokaryotic cell type.

Besides bacteria, cyano bacteria are major group of prokaryotes. The other domain of the prokaryotes is archae bacteria that live in extreme environment.

Prokaryotes’ genetic information is typically in the form of a nucleoid of DNA strands, but they also have additional DNA in the form of a circular loop known as a plasmid. Although prokaryotes lack cell organelles, they do have a few internal structures such as cytoskeletons, ribosomes, and vacuoles.

Characteristics

Bacterial cells are typically spherical, rod-shaped, or spiral in shape, with diameters ranging from 1 to 10 µm, but they can range in size from 0.2 m to 750 µm. Their DNA content ranges from 0.6 million to 5 million base pairs, which is enough to encode approximately 5000 different proteins. Cyanobacteria, bacteria that evolved photosynthesis, are the largest and most complex prokaryotes.

Cocci-spherical

Bacilli-rod shaped

Spirochaete-spiral shaped

Vibrio-comma shaped

Prokaryotic cell

Prokaryotic Cell Structure and Function of Organelles

Morphological Types

Prokaryotic cell

Escherichia coli (E. coli) illustrate the structure of a typical prokaryotic cell; the cell is rod-shaped, about 1 μm in diameter, and about 2 μm long. E.coli, like most other prokaryotes, has a rigid cell wall made of polysaccharides and peptides. The plasma membrane, a bilayer of phospholipids and associated proteins, is found within the cell wall.

The cell wall is porous and easily penetrated by a wide range of molecules, whereas the plasma membrane serves as a functional barrier between the cell’s interior and its external environment. E.coli DNA is a single circular molecule in the nucleoid that is not surrounded by a membrane that separates it from the cytoplasm. The cytoplasm contains approximately 30,000 ribosomes (protein synthesis sites), which contributes to its granular appearance.

A Component of Prokaryotic Cells

Cell wall

The cell wall a component of prokaryotic cells is the outermost layer of most cells that protects and shapes the bacterial cell. Mycoplasma is an exception because it lacks a cell wall. Bacterial cell walls are composed of peptidoglycan, which is composed of polysaccharide chains that are linked together by unusual peptides containing D-amino acids.

Bacterial cell walls differ from plant and fungi cell walls, which are composed of cellulose and chitin, respectively. The cell wall of bacteria differs from that of Archaea, which lacks peptidoglycan. Many bacteria rely on their cell walls to survive.

The antibiotic penicillin kills bacteria by preventing peptidoglycan cross-linking, which causes the cell wall to weaken and lyse. Gram-positive and Gram-negative cell walls are the most common types of cell walls found in bacteria.

Prokaryotic cell

Membrane

It is a phospholipid bilayer with associated proteins a component of prokaryotic cells. This semipermeable membrane regulates the flow of substances into and out of the cell. Substances are transported either actively or passively.

Cytoplasm

Cytoplasm a component of prokaryotic cells. It contains many enzymes that catalyze metabolic chemical reactions, as well as DNA in a region known as the nucleoid. Ribosomes can be found in the cytoplasm as well.

Ribosomes

Ribosomes a component of prokaryotic cells, they are the sites where proteins are synthesized. Translates messenger RNA, which aids in protein synthesis.

Nucleoid

Naked DNA a component of prokaryotic cells region that stores the hereditary material (genetic information) that controls the cell and is passed down to daughter cells.

Pili

A pilus a component of prokaryotic cells is typically 6 to 7 nm in diameter. They help bacteria to adhere with each other for the exchange of genetic material.

Flagella

Most prokaryotes have a long, whip-like protrusion a component of prokaryotic cells that aids in cellular locomotion. Aside from its primary function of locomotion, it is also a sensory organelle, sensitive to chemicals and temperatures outside the cell.

Plasmids

They are double-stranded, circular structures of extra chromosomal DNA . Their sizes range from 1 to 1,000 kbp. They carry genes that code for a variety of metabolic activities, allowing their host bacteria to degrade pollutant compounds and produce antibacterial proteins.

They can also carry virulence genes, which aid in the pathogenicity of bacteria that cause diseases such as plague, dysentery, anthrax, and tetanus. They are also responsible for the spread of antibiotic resistance genes, which has an impact on disease treatment. Plasmids are classified into four types.

Fertility plasmids

Fertility plasmids a component of prokaryotic cells contain TRA genes (also transfer operons or TRA operons) and are conjugation-capable.

Resistance plasmids

Resistance plasmids a component of prokaryotic cells contain genes that can help bacteria develop resistance to antibiotics or toxins, as well as help them produce pili.

Col plasmids

Col plasmids a component of prokaryotic cells contain genes that code for bacteriocins, which are proteins that kill other bacteria.

Degradative plasmids

Degradative plasmids a component of prokaryotic cells allow the metabolism of uncommon substances such as toluene and salicylic acid.

Pathogenicity plasmids

These plasmids allow the bacterium to become pathogenic. Pathogenic bacteria are bacteria that can cause disease.

Capsule

The capsule a component of prokaryotic cells is found in some bacterial cells; this extra outer covering protects the cell when it is engulfed by phagocytes and viruses, aids in moisture retention, and aids in the cell’s adhesion to surfaces and nutrients.

The capsule is found most commonly among Gram-negative bacteria. Escherichia coli, Klebsiella pneumoniae Haemophilus influenzae, Pseudomonas aeruginosa and Salmonella are some examples Gram-negative bacteria possessing capsules. Examples of Gram positive bacteria that possess capsules are Bacillus megaterium, Streptococcus pneumoniae, Streptococcus pyogenes.

Reproduction

Binary fission

Binary fission is a type of asexual reproduction in which a single living cell or organelle doubles in size before splitting into two identical daughter cells, each of which has the potential to grow to the size of the original cell or organelle.

Many prokaryotes, including archaea, cyanobacteria, and eubacteria, reproduce via binary fission. During this process, the parent cell’s genetic material is evenly divided into two daughter cells. As a result, there is no genetic variation in newly formed prokaryotic cells.

The cell’s DNA divides to form two identical DNA molecules, which are both moved towards the cell membrane. The cell then doubles in size, and the cell membrane gradually begins to divide, with each cell containing a copy of the DNA. Once the cell membrane has been divided, the cell wall forms between the two strands of DNA, dividing the parent cell into two identical daughter cells.

Recombination

Recombination is another asexual mode of reproduction. Transduction, transformation, and conjugation are all used to incorporate the genetic material of one cell into the cell of another prokaryote. During conjugation, two cells are linked by sex pilli, through which genes are transferred.

Prokaryotic cell takes up genetic material from the environment and incorporates it into the bacterial chromosome during transformation. Transduction involves the exchange of genes via viral infection. The bacteriophage infects one bacterium before stealing the targeted gene and transferring it to another cell.

Further Readings

Reference