MCSF Flashcards
➢ Their DNA is not enclosed within a
membrane and is usually a singular
circularly arranged chromosome.
▪ Some bacteria have two chromosomes
(Vibrio cholerae),
▪ Some have linearly arranged chromosome
➢ Their DNA is not associated with
histones (special chromosomal proteins
found in eukaryotes)
Prokaryotic Cell
➢They lack membrane-bound organelles.
➢Their cell wall almost always contain the complex polysaccharide peptidoglycan.
➢They usually divide by binary fission
Prokaryotic cells
The size, shape, and arrangement of bacterial cells
➢Vary in shape and sizes
➢ Most bacteria range from 0.2 to 2.0 μm in diameter and
from 2 to 8 μm in length.
➢They have a few basic shapes:
▪spherical = coccus (plural: cocci, meaning berries)
▪rod-shaped = bacillus (plural: bacilli, meaning little staffs)
▪ spiral
➢ usually round but can be oval,
elongated, or flattened on one
side.
➢ When cocci divide to reproduce,
the cells can remain attached to
one another
Cocci
Types of Cocci
Diplococci
Streptococci
Tetrads
Sarcinae
Staphylococci
cocci that remain in pairs after
dividing
Diplococci
those that divide and remain
attached in chainlike patterns
Streptococci
- those that divide in two planes and
remain in groups of four
Tetrads
those that divide in three planes and
remain attached in cube-like groups of eight
Sarcinae
those that divide in multiple
planes and form grape-like clusters or broad
sheets
Staphylococci
➢ divide only across their short axis, so there are fewer groupings of bacilli than of cocci.
Bacilli
Types of Bacilli
❑ Single bacilli
❑ Diplobacilli
❑ Streptobacilli
❑ Coccobacilli
- Most bacilli appear as
single rods
Single bacilli
appear in pairs after
division
Diplobacilli
- occur in chains
Streptobacilli
oval and look so much
like cocci
Coccobacilli
➢ have one or more twists
➢ they are never straight
Spiral
Types of Spiral
❑ Vibrios
❑ Spirilla
❑ Spirochetes
- Bacteria that look like
curved rods
Vibrios
- have a helical shape, like a
corkscrew, and fairly rigid bodies
Spirilla
- group of spirals which
are helical and flexible
Spirochetes
- group of spirals
which are helical and flexible
▪ Unlike the spirilla, which use propellerlike external appendages called
flagella to move, spirochetes move by
means of axial filaments, which
resemble flagella but are contained
within a flexible external sheath.
Spirochetes
Other shapes
➢ star-shaped cells (genus Stella);
➢ rectangular, flat cells (halophilic
archaea) of the genus Haloarcula; and
➢ triangular cells.
The shape of a bacterium is determined by
heredity
Generally, most bacteria are
monomorphic
However, a number of environmental conditions can
alter that shape.
‒ If the shape is altered, identification becomes difficult.
Moreover, some bacteria, such as and
Corynebacterium, are generally
pleomorphic
Structure of a Typical Prokaryotic Cell
➢ components according to the
following organization:
(1) structures external to the cell wall,
(2) the cell wall itself, and
(3) structures internal to the cell wall
Among the possible structures external to the
prokaryotic cell wall are the:
❑ Glycocalyx
❑ Flagella
❑ Axial filaments
❑ Fimbriae
❑ Pili
➢ meaning ‘sugar coat’,
➢viscous (sticky), gelatinous polymer that is external to
the cell wall and composed of polysaccharide, or
polypeptide, or both
➢ made inside the cell and secreted to the cell surface
Glycocalyx
If the substance is organized and is firmly attached to the
cell wall, the glycocalyx is described as a
capsule
If the substance is unorganized and only loosely
attached to the cell wall, the glycocalyx is described as a
slime layer
➢ Important in contributing to bacterial virulence (the
degree to which a pathogen causes disease).
➢ protect pathogenic bacteria from phagocytosis by the
cells of the host
Capsules
produces a capsule of d-glutamic acid
Bacillus anthracis
is any group of microorganisms in which cells
stick to each other on a surface.
‒These adherent cells are frequently embedded within a selfproduced matrix of extracellular polymeric substance
(EPS).
Biofilm
protects the cells within it, facilitates communication among
them, and enables the cells to survive by attaching to various
surfaces in their natural environment.
extracellular polymeric substance
(EPS).
➢long filamentous appendages that
propel bacteria
Flagella
Flagella may be:
- atrichous
- peritrichous
- polar
(lack flagella or without projections);
atrichous
distributed over the entire cell)
peritrichous (