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A Handbook of Biology

ÇËLL ØRGÅÑËLLËS ÏÑ PRØKÅRÝØTÏÇ ÇËLLS

1.

Cell Envelope

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It is a chemically complex protective covering.

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It is made of 3 tightly bound layers.

Glycocalyx: Outer layer.

Its composition and

thickness vary in different

bacteria. It may be a

slime layer (loose sheath)

or capsule (thick & tough).

(Karnataka NEET 2013)

Cell wall: Middle layer.

Seen in all prokaryotes.

It gives shape to the cell

and provides a structural

support to prevent the

bacterium from bursting

or collapsing

1

2

Plasma membrane: Inner layer. It is semi-permeable in

nature and interacts with the outside. This is structurally

similar to that of the eukaryotes.

3

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Based on the type of cell envelop and response to Gram staining,

bacteria are of two types:

Gram positive: They take up and retain the gram stain.

Gram negative: They do not retain the gram stain.

2. Mesosomes & Chromatophores (Membranous structures)

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Mesosome is formed by the extensions of plasma membrane. These

extensions include vesicles, tubules & lamellae.

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Functions: Mesosomes help

–

In cell wall formation.

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In DNA (chromosome) replication.

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In distribution of chromosomes to daughter cells.

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In respiration and secretion processes. (AIPMT 1997)

–

To increase the surface area of the plasma

membrane and enzymatic content.