Prokaryotic cell explained with its structure

Prokaryotic Cell:

Recall that a cell is defined as the basic, structural and functional unit of life.

Generally, cells are put into two types based on the presence or absence of a well-defined nucleus within it, alongside their specific setups. These are:

1. Prokaryotic Cell 

2. Eukaryotic Cell
   Please read on eukaryotic cell explained with its characteristics here.

Prokaryotic cells (or prokaryotes) are unicellular organisms lacking a definitive nucleus. They have a cell size ranging from 0.1 to 0.5 µm (micrometer) in diameter, and are typically in the domain of archaea, cyanobacteria and bacteria. Generally, prokaryotes are found everywhere on earth, be it on land, water and air, including inside living organisms.

Please read an introduction to cell here.

The prokaryotes 'archaea' are ancient organisms that thrive under extreme conditions. As an instance, Pyrolobus fumarii is an archaea that lives in hydrothermal vents with temperatures around 113 ^oC or 235 ^oF.

The Picrophilus are another group of archaeans that live in soils with an acidic pH as low as zero. In fact, they are the most acid-tolerant organisms known on earth.

The methanogens are another group of archaeans found in places without oxygen (anaerobic environment) such as hot springs, intestines of animals and marshes. Such methanogens include Methanobrevibacter gottschalkii, Methanococcus maripaludis, Methanogenium frigidum, Methanopyrus kandleri, Methanosaeta concilii, Methanosarcina barkeri, and Methanosphaera stadtmanae.

Please read on swamp forest here.

Cyanobacteria are prokaryotes, and were formerly termed as blue-green algae. They are known to manufacture their own food through a process termed photosynthesis. They are able to do this as a result of the green pigment (chlorophyll) present within their cell. They constitute a large number of the aquatic ecosystem, that is: oceans, seas, rivers, lakes and ponds respectively.

Please read on photosynthesis and chemosynthesis here.

Bacteria are considered as one of the most popular prokaryotes on earth due to their harmful and beneficial actions to other organisms. For instance, numerous beneficial bacteria are present in the colon of humans and ruminants. However, some could be harmful; for example, certain strains of Escherichia coli (E. coli O157:H7) present in the intestines of animals.

Note: the population of bacteria inside the human body is higher than the total number of human beings living on earth.

You can read interesting facts for students here.

• The existence of prokaryotes had been dated back to over five billion years. Interestingly, fossil fuels had shown the existence of prokaryotes, and it is believed by scientists that they metamorphosed into various forms of life existing on earth.
  

  Please read on ecological concepts here.

Prokaryotic Cell

Structure of a Prokaryote

The above image will serve as a reference towards the explanation on various structures of a prokaryotic cell.

The prokaryotic cell is bounded by a plasma membrane (or cell membrane), cell wall and an outermost capsule. The cell membrane is semipermeable. This means that it can allow the entry and exit of certain substances, while denying others. Also, it can be utilized for respiratory activities.

Please read the characteristics of living organisms here.

The cell wall is present just after the cell membrane and before the capsule. It is made up of peptidoglycan (or murein), which is a polymer of sugars and amino acids. It functions to protect the cell from unfavorable external conditions, prevents it from bursting, and also gives the prokaryotic organism its shape.

Alongside the cell wall, an outer protective layer called capsule may also be found in the cells of bacteria. They are formed from capsular polysaccharides (CPSs) with varying structures. The capsule functions to preserve and protect the cell form being digested or dissolved (through phagocytosis) by enzymes or other foreign cells. Together with the slime layer, it aids the attachment of the bacteria to nutrients and adjacent cells. Meanwhile, understand that the capsule have also got good water retention ability.

You can read amazing facts in biology here.

Prokaryotic cell do not have a definite nucleus, neither do they have nuclear membrane. They have a chromosomal Deoxyribonucleic Acid (DNA), typically present on a single chromosome. Such DNA is crucial for their sexual reproduction. However, they may also have non-chromosomal DNA materials called plasmids, and these are not required in reproduction. The location of the prokaryotic genetic materials are somewhere in a cytoplasmic region termed as nucleoid, and this could be spiral, spherical, rod-like or irregular in shape.

The nucleoid in prokaryotes is the region in the cytoplasm where genetic material is located.

You can read on the contents of the scrotum in humans here.

Note: Plasmids are non-chromosomal DNA structures in prokaryotes. As a result, they are not involved in reproduction.

Prokaryotic cells often have pili. These are short proteinous hairlike structures used for attachment to the surface of other cells. They may be utilized for the cell's movement, but more importantly, they initiate the infectious and virulent properties of harmful bacteria. However, some prokaryotes may also have a whiplike structure called flagella which serves locomotary purposes for the cell.

The appendages for locomotion are called protrusions, and are often found on the surfaces of prokaryotic cells. They include flagella, fimbriae and pili.

You can read on protists explained with their characteristics here.

• Sex pili may also be present in prokaryotes, and are utilized for DNA exchange.

The cytoplasm is a gel-like fluid filled space within the plasma membrane of a prokaryotic cell. It is composed mainly of cytosol, ribosomes, inclusions, cytoskeleton, enzymes and salts.

The mitochondria, golgi apparatus and endoplasmic reticulum are all absent in prokaryotes. However, ribosomes may be present, and are involved in protein synthesis.

You can attempt Len Academy questions on various subjects here.

Reproduction in prokaryotes can occur either sexually or asexually. Asexual reproduction is typically through a process termed binary fission, while sexual reproduction occurs through gene recombination.

Gene recombination in prokaryotes can be achieved via the following methods:

1. Conjugation

2. Transformation

3. Transduction
   Please read on the characteristics of prokaryotes alongside their reproduction here. here.