8.4. Prokaryotic Cells

The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms). They are generally smaller and multiply more rapidly than the eukaryotic cells. They may vary greatly in shape and size. The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).

Prokaryotic cells are a type of cell that lack a true nucleus and other membrane-bound organelles. They are typically smaller than eukaryotic cells and reproduce faster. The shape of prokaryotic cells can vary significantly, with the main types being rod-shaped (bacillus), spherical (coccus), comma-shaped (vibrio), and spiral (spirillum). This diversity in shape can affect how they function and survive in different environments.

Think of prokaryotic cells like different types of vehicles: some are like buses (bacillus), others like balls (coccus), some are like motorcycles (vibrio), and others are like bicycles (spirillum). Each serves a different purpose and can navigate various paths depending on their design.

The organisation of the prokaryotic cell is fundamentally similar even though prokaryotes exhibit a wide variety of shapes and functions. All prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma. The fluid matrix filling the cell is the cytoplasm. There is no well-defined nucleus. The genetic material is basically naked, not enveloped by a nuclear membrane.

Despite their shape differences, all prokaryotic cells share a basic structure. They have a protective cell wall that encases the cell membrane, with cytoplasm filling the inside. Unlike eukaryotic cells, prokaryotic cells do not have a nucleus; instead, their genetic material (DNA) floats freely in the cytoplasm. This lack of membrane-bound organelles is a hallmark of prokaryotic cells.

Imagine a prokaryotic cell like a simple bag filled with jelly (cytoplasm) and a string (DNA) that is loosely hanging inside it. In this case, the bag represents the cell wall and membrane, while the jelly does not contain any compartments, reflecting the simplicity of prokaryotic cells.

The genetic material is basically naked, not enveloped by a nuclear membrane. In addition to the genomic DNA (the single chromosome/circular DNA), many bacteria have small circular DNA outside the genomic DNA. These smaller DNA are called plasmids, which confer certain unique phenotypic characters to such bacteria, such as resistance to antibiotics.

The DNA in prokaryotic cells is organized differently than in eukaryotic cells. It is typically circular and exists in a single chromosome, not enclosed by a nuclear membrane. Furthermore, many prokaryotes have plasmids, small loops of DNA that can carry genes that provide advantages, like antibiotic resistance. This unique way of storing and transferring genetic information is crucial for their adaptability and survival.

Consider plasmids as small bonus cards that give bacteria special powers, like immunity to certain medicines. Just like a game character that can gain extra abilities, bacteria can become resistant to antibiotics, allowing them to survive in hostile conditions that would typically kill others.

Most prokaryotic cells, particularly the bacterial cells, have a chemically complex cell envelope. The cell envelope consists of a tightly bound three layered structure: the outermost glycocalyx, followed by the cell wall, and then the plasma membrane. Although each layer of the envelope performs distinct functions, they act together as a single protective unit.

Prokaryotic cells have a cell envelope that provides structural integrity and protection. This envelope is made up of three layers: the glycocalyx (a protective layer), the cell wall (which gives the cell its shape and protects it from the environment), and the plasma membrane (which regulates what enters and exits the cell). Each layer has a specific function, but they work together to keep the cell safe and functional.

Think of the cell envelope like the layers of an onion. Each layer serves a purpose—keeping the onion intact and safe from the environment, just as each layer of the cell envelope protects the prokaryotic cell.

Bacterial cells may be motile or non-motile. If motile, they have thin filamentous extensions from their cell wall called flagella. The bacterial flagellum is composed of three parts – filament, hook and basal body. Bacteria show a range in the number and arrangement of flagella.

Some prokaryotic cells can move using structures known as flagella, which are long, hair-like appendages. Flagella are crucial for motility, consisting of three main components: the filament (the longest part), the hook (which connects the filament to the basal body), and the basal body (which anchors the flagellum in the cell wall). This allows bacteria to swim through liquid environments, which is essential for finding nutrients and escaping predators.

Consider flagella like the tail of a fish. Just as a fish uses its tail to swim through water, bacteria use their flagella to propel themselves in their aquatic environments, allowing them to navigate toward food or away from danger.

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