Q.What is a plasmid? What is its significance?

Pleomorphic bacteria lack a single fixed cell shape and can display multiple forms; Mycoplasma is a classic example.

Pleomorphic bacteria

Most bacteria have a fixed, characteristic shape (coccus, bacillus, vibrio, spirillum). However, some bacteria lack a rigid, well-defined cell wall or have a wall that permits variation in shape, so a single species can exist in several different shapes at different times or under different conditions. Such bacteria are called pleomorphic.

Example …

Pleomorphic bacteria lack a rigid cell wall of fixed shape, so a single species can show several different cell shapes; Mycoplasma is the classic example.

Most bacteria have a rigid cell wall (peptidoglycan-based) that fixes them into one of the standard shapes — coccus, bacillus, vibrio or spirillum. Pleomorphic bacteria are an exception: their cell wall is thin, flexible or, in some cases, absent, so the same organism can be seen as spherical, rod-shaped, filamentous or irregular depending on growth conditions and stage of the life cycle.

Key features:

• No single, genetically fixed morphology — shape varies within a population/species.
• Usually correlated with a reduced or absent peptidoglycan wall.
• Makes identification by shape alone unreliable for these genera. …

Porins are pore-forming outer-membrane proteins that permit passive diffusion of small hydrophilic solutes into bacterial cells.

What porins are:

Porins are transmembrane proteins present in large numbers in the outer membrane of gram-negative bacteria (and also found in mitochondrial and chloroplast outer membranes). Each porin molecule spans the membrane and forms a water-filled channel or pore.

Role in diffusion:

• Porins allow the passive diffusion of small, water-soluble molecules (generally below about 600-700 Da) such as ions, sugars, amino acids and other nutrients across the otherwise impermeable outer membrane.
• Because the process is passive (down the concentration gradient), it does not require metabolic energy. …

A genophore is the naked, circular DNA molecule of a prokaryote (or of an organelle like a chloroplast/mitochondrion) that acts as the chromosome but is not enclosed by a nuclear membrane.

In eukaryotes the genetic material (DNA) is organised into chromosomes enclosed within a membrane-bound nucleus and is associated with histone proteins. In prokaryotes such as bacteria, there is no true nucleus. Their genetic material is:

• A single, circular, double-stranded DNA molecule.
• Naked (not wrapped around histones as in eukaryotes).
• Lying free in the cytoplasm in a region called the nucleoid, without a nuclear membrane. …

Pleomorphic bacteria show multiple/variable shapes rather than one fixed morphology, typically because they lack a rigid cell wall; Mycoplasma is the classic example.

Most bacteria have a rigid cell wall (made of peptidoglycan/murein) that gives them a fixed, characteristic shape — coccus (spherical), bacillus (rod-shaped), vibrio (comma-shaped), or spirillum (spiral). This fixed shape is maintained because the rigid wall resists changes in cell shape.

Pleomorphic bacteria, in contrast, either lack a cell wall entirely or have a very thin, flexible one. Because there is no rigid structure constraining their shape, these bacteria can assume a variety of forms — spherical, oval, filamentous, or irregular — even within a single population, and their shape can change depending on the surrounding environment/growth conditions. The term 'pleomorphic' literally means 'many forms'.

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Genophore is the term used for the 'chromosome equivalent' of prokaryotes such as bacteria.

Bacteria (prokaryotes) lack a true, membrane-bound nucleus. Their genetic material — a single, large, circular double-stranded DNA molecule — lies condensed in an irregularly shaped region of the cytoplasm called the nucleoid. This DNA is not organised into chromosomes associated with histone proteins the way eukaryotic DNA is; instead it is 'naked' DNA (though it is associated with some non-histone, DNA-binding proteins) that is supercoiled and looped to fit inside the cell.

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Pleomorphic bacteria can occur in more than one shape, unlike typical bacteria that have a fixed, characteristic shape.

Most bacteria have a rigid cell wall that gives them a fixed, characteristic shape (coccus, bacillus, spirillum, vibrio). However, some bacteria lack a rigid cell wall, or have a wall that is not well-defined. Since there is nothing to hold a fixed outline, such bacteria can occur in variable shapes — this is termed pleomorphism, and such bacteria are called pleomorphic bacteria.

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