Page 12 - Biology_F5

Cytology

Beneath the cell wall, there is a plasma photosynthesis) and nitrogen fixing
membrane, which is a double layer of membrane (for nitrogen fixing bacteria).
phospholipids associated with proteins Beneath the cell membrane, there is
and other molecules. It protects the cytoplasm, a gel-like fluid filling the cell.
intracellular materials and it regulates the It is a place where cellular organelles such
movement of materials into and out of the as ribosomes are suspended. Ribosomes
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cell. In some bacteria, there is infolding of (70s) are small structures in the cytoplasm
the cell membrane that forms mesosome that play crucial role in protein synthesis
(which appears to be associated with within the bacterial cell (Figure 1.2). The
DNA during cell division, and also used 70s refers to the rate of sedimentation of
for respiration), photosynthetic membrane the ribosome in a centrifuge, "s" is a unit
(which contain photosynthetic pigment of measurement called svedberg unit.
such as bacteriochlorophyll used for

Additional structures sometimes Structures always present
present
Flagellum

Capsule Cell wall
Infolding of cell surface membrane
Cell surface membrane
Mesosomes Cytoplasm
Circular DNA

Plasmid
Ribosomes
Pili

Figure 1.2: The structure of a typical prokaryotic cell

The prokaryotic cell consists of the bacteria through pili during conjugation
nucleoid, a region of the prokaryotic process.
cytoplasm containing the genome, which
is the main genetic material (Figure 1.3). Most bacteria have a slender tubular
It possesses a single, circular DNA with structure on the cell wall called pili. There
a double-stranded DNA molecule. Some are two types of pili. The first type of pilli
bacteria have additional genes located in is used by related bacteria to exchange
small circular molecules of DNA called genetic materials through the process
plasmids. These genes play roles in of conjugation while the second type of
maintaining virulence to bacteria, such pili enables bacteria to stick to their host
as developing resistance to drugs. The or substrate, which increases chances of
resistant genes can be exchanged between infection.

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