The document discusses the anatomy and structure of bacterial cells. It describes the key components of the bacterial cell including the cell envelope, cell wall, cytoplasmic membrane, and optional extracellular structures like capsules and slime layers. The cell wall and envelope structures differ between gram-positive and gram-negative bacteria, affecting how they retain stains used in the Gram staining procedure. The structures work together to maintain cell shape, transport nutrients and waste, generate energy, and provide protection.

1. Anatomy of the
bacterial cell
Prof. Dr. Nidhal Raoof Mahdi

2. The importance of microbiology:
1. Microorganisms are required for the production of bread, cheese, yogurt,
alcohol, wine, beer, antibiotics (e.g. penicillin, streptomycin), vaccines, vitamins,
enzymes and many more important products.
2. Microorganisms are necessary components of our ecosystem.
Microorganism play an important role in the recycling of organic and inorganic
material through their roles in the C, N and S cycles, thus playing an important part
in the maintenance of the stability of the biosphere.
3. The use of microbes to reduce or degrade pollutants, industrial waste and
household garbage, a new area referred to as bioremediations being given
substantial importance these days.
4. A common edible mushroom contains a protein lectin that can stop cancer
cell multiplication. This discovery of 21st century could lead to new targets for
therapy.

3. Anatomy of the bacterial cell
• Bacterial Cell Components can
be divided into:
• A‐ Cell envelope and its
Appendages
• a. The outer layer or cell
envelope consists of two
components:
• 1. Cell wall.
• 2. Cytoplasmic membrane or
plasma membrane—beneath
cell wall.
• b. Cellular appendages—Besides
these essential components,
some bacteria may possess
additional structures such as
capsule, slime layer, pili or
fimbriae and flagella.

4. Anatomy of the bacterial cell
• B. Cell Interior
• Those structures and
substances that are
bounded by the cytoplasmic
membrane include
cytoplasm, cytoplasmic
inclusions (mesosomes,
ribosomes, inclusion
granules, vacuoles) a single
circular chromosome of
deoxyribonucleic acid (DNA)
, plasmid and endospore.

5. Bacterial Cell Structures and function
• A‐ Cell envelope and its Appendages
• 1. Cell Wall
• The cell wall is the layer that lies just
outside the plasma membrane. It is 10‐25
nm thick, strong and relatively rigid.
Functions of the cell wall:
1. Maintains the characteristic shape of the bacterium
and rigidity to the cell.
2. It supports the weak cytoplasmic membrane against
the high internal osmotic pressure of the protoplasm.
3. It takes part in cell division.
4. Also functions in adhesion with other bacteria and
with mammalian cells.
5. Provide specific protein and carbohydrate receptors
for the attachment of some bacterial viruses.

6. STRUCTURE and CHEMICAL COMPOSITION of the cell wall
The Gram‐positive cell wall is a
uniformly thick layer of
peptidoglycan (murein) external to
the plasma membrane.
Chemically the cell wall is composed
of peptidoglycan consists of three
parts:
1. A backbone—composed of
alternating N‐acetylglu¬cosamine
(NAG) and N‐acetylmuramic acid
(NAM).
2. A set of identical tetrapeptide side
chains attached to N‐acetylmuramic
acid.
3. A set of identical pentapeptide
cross‐bridges.
Teichoic acid and lipoteichoic acid are present in the cell wall of Gram positive
but absent in Gram negative bacteria.

7. The walls of Gram ‐ve species
• are generally thinner (10‐15
nm) than those of Gram +ve
species (20‐25 nm). It consists
of a relatively thin
peptidoglycan sheet between
the plasma membrane and a
phospholipid‐
lipopolysaccharide outer
membrane. Cell wall of Gram‐
negative organisms is more
complex as it has a layer of
lipoprotein, outer membrane
and polysaccharide.

8. The walls of Gram ‐ve species
• The Periplasmic space,
the cell wall of the Gram ‐
ve bacteria have space
between the inner and
outer membranes, called
the periplasmic space,
contains the
peptidoglycan layer and a
gel‐like solution of
proteins.

9. the outer layer Gram‐negative cell walls being made up of
lipopolysaccharide;
*this has three
parts:
1‐lipid A
2‐core
polysaccharide
3‐an O‐specific side
chain(O‐antigein):
sugars that are
repeated several
times and are
specific for each
species/strain.

10. the outer layer Gram‐negative cell walls being made up of
lipopolysaccharide;
*this has three parts:
1‐lipid A
2‐core polysaccharide
3‐an O‐specific side chain(O‐antigein):
sugars that are repeated several times and
are specific for each species/strain.
• The lipid A component has toxic
properties known as an endotoxin, which,
if released into the bloodstream, can lead
to serious conditions such as fever and
toxic shock.
• (Endotoxins: are the structural
component of G‐V bacteria, which is
released after bacterial cell lysed.)

11. Gram‐Ve bacteria

12. Most bacteria are
classified as gram
positive or gram
negative according to
their response to the
Gram‐staining
procedure. This
procedure was named
for the Danish scientist
Hans Christian Gram
(1884).

14. The Gram stain depends on the
ability of certain bacteria (the gram‐
positive bacteria) to retain a complex
of crystal violet (a purple dye) and
iodine after a brief wash with alcohol
or acetone. Gram‐negative bacteria
do not retain the dye–iodine
complex and become translucent,
but they can then be counterstained
with safranin (a red dye). Thus,
gram‐positive bacteria look purple
under the microscope, and gram‐
negative bacteria look red.

15. Comparison of Features of Gram‐ Positive and Gram‐Negative Bacteria:

16. Cell walls of some bacteria such
as the
Mycobacterium tuberculosis have
cell walls that contain large
amounts of waxes, known as
mycolic acids; that are resistant
to Gram staining; these bacteria
are called acid‐fast organisms.

17. Eubacteria Lacking Cell Walls:
Mycoplasmas naturally lack cell
walls; they are enclosed by the
plasma membrane and can grow
on ordinary media. They occur
in nature and may cause human
diseases (e.g. pneumonia).

18. 2‐Cytoplasmic Membrane (plasma membrane):
The bacterial cytoplasmic membrane
is 5 to 10 nm in thickness and
composed of a phospholipid bilayer
with proteins inserted into it.
functions of a cell membrane such as
1. retains cytoplasm (cytoplasm +
plasma membrane = protoplast)
2. selectively permeable barrier;
transport of nutrients and wastes
3. generation of energy; biosynthesis

21. 2‐Cytoplasmic Membrane (plasma membrane):
Mesosome: The outer
membrane of cytoplasm
forms much coiled
invagination to provide larger
surface area. The surface of
mesosome has many
respiratory enzymes, which
takes part in respiration. It is
absent in eukaryotic cells.

22. 3‐ Optional layers outside cell wall: Glycocalyx
(capsule &slime layer)
Capsules and slime layers
usually are composed of
polysaccharides, a
glycocalyx is a network of
polysaccharides extending
from the surface of
bacteria.

23. a) Capsule
•Sharply defined viscous layer secreted
around the cell wall and attached tightly.
•Polysaccharide/ polypeptide in nature.
•Protects bacteria from lytic enzymes.
•inhibits phagocytosis; hence, the
presence of a capsule correlates with
virulence.
Its polysaccharides are used as
antigens in certain vaccines.
•Stained by negative staining using
Indian Ink.

24. b) slime layer
• is a polysaccharide coating that
covers the outer surfaces of many
bacteria.
• it is loosely associated with the
bacterium and can easily wash off.
• allows the bacteria to adhere
firmly to various structures, e.g.
oral mucosa, teeth ،heart valves
and catheters. contribute to the
formation of biofilms.

25. 4‐Bacterial Flagellum: Flagella
‐ Hair‐like appendage on the
bacterial surface that is
responsible for movement
(motility).
‐ A bacterial flagellum is made
up of protein subunit called
flagellin.
‐ flagellin is highly antigenic;
so, it can be used for
identification (H‐antigen).
‐ Function: movement;
chemotaxis (movement towards
food and away from toxics).

26. Structure:
1. Filament
2. Hook: composed of
multiple subunits of one
protein
3. Basal body: insert in
the cytoplasmic
membrane and outer
membrane of bacteria.

27. Flagellum arrangement
Monotrichous: single polar
flagellum
Lophotrichous: multiple flagella at
single pole
Amphitrichous: flagella at both
poles
Peritrichous: flagella distributed all
around

28. 5‐Pili (Fimbriae)
Hair‐like appendage on the
bacterial surface called pili
or fimbriae. They are
shorter and finer than
flagella; similar to flagella,
they are composed of
structural protein subunits
termed pilins. They are
important for virulence
Two classes can be
distinguished:
1‐ ordinary pili (frequently
referred to as fimbria),
which play a role in the
adherence to the host cells

29. 2‐sex pili,
which are
responsible for
the
attachment in
bacterial
conjugation

30. B. Cell interior
Cytoplasm
Jelly intracellular environment
composed largely of water
(80%), proteins, nucleic acids,
lipids, salts, sugars, and various
low molecular weight molecules.
The cytoplasm also harbors:
Nucleoid, ribosomes, Inclusion
bodies, plasmids and endospore.

31. B. Cell interior
*Nucleoid: In prokaryotes
nuclear membrane and nucleolus
are absent. It contains a single
chromosome consisting of a
single circular DNA filament. The
genetic material DNA is present
in the cytoplasm without histone
proteins.

32. B. Cell interior
*Ribosomes: Bacteria contain a
group of ribosomes called
polyribosomes present in the
cytoplasm of the cell. Composed
of ribosomal RNA (rRNA) and
proteins. It is 70S type in
bacterial cell having two
subunits. Ribosomes help in
protein synthesis.

33. B. Cell interior
*Inclusion bodies
Certain bacteria may contain
within their cytoplasm granular
structures known as inclusion
bodies. These act as food
reserves, and may contain
organic compounds such as
starch, glycogen or lipid. In
addition, Sulphur and
polyphosphate can be stored as
inclusion bodies.

34. B. Cell interior
*Plasmids
‐ Small extra‐chromosomal
double stranded DNA.
‐ not essential for survival.
‐Transmitted to daughter cells
during binary fission
‐ Often encode antibiotic
resistance.

35. Endospore
Well known spore formers:
Bacillus anthracis
Clostridium botulinum, Clostridium tetani
‐ A number of gram‐positive bacteria,
such as those of the genera Clostridium
and Bacillus can form a special resistant
dormant structure called an endospore.

36. Endospore develop (sporulation) occurs
when essential nutrients are depleted
(carbon, nitrogen, or phosphorous).
‐ Endospore is highly resistant to heat,
dryness, radiation, chemicals.
‐Dormant endospores can survive for many
years.
‐Commonly found in the soil.
‐ endospore‐formation is a mechanism of
survival rather than a mechanism of
reproduction.

37. Endospore
‐ Under favorable
conditions,
endospores
germinate (change)
into vegetative
(standard) cells again
and are able to
replicate.

38. Structure of the endospore
The spore has a core wall of
unique peptidoglycan
surrounded by several layers,
including the cortex,
the spore coat and the
exosporium.
The dehydrated core contains the
bacterial chromosome and
a few ribosomes and enzymes

39. Types of spores:
1. Central, bulging
2. Central, not bulging,
3. Subterminal, bulging,
4. Subterminal, not bulging,
5. Terminal, spherical,
6. Terminal, oval

40. Stages of endospore formation:
1‐DNA of mother cell condenses
2‐Transeverse wall begins to form
3‐Spore material separated;
formation of forespore at one end
of a cell
4‐Vegetative cell grows around
spore
5‐Spore forms multilayered
coating
6‐Cell releases free spore

41. Germination
The germination process
occurs in three stages:
activation, initiation, and
outgrowth.
1‐Activation:
Most endospores cannot
germinate immediately
after they have formed,
but they can germinate
after
activated in a nutritionally
rich medium by damages
the spore coat.

42. Germination
.
2‐ Initiation:
initiate germination if the
environmental conditions are
favorable.

43. Germination
3‐Outgrowth:
requires a supply of all
nutrients essential for cell
growth which terminates
in cell division (binary
fission).

44. Taxonomy:
(systematic classification of organisms into groups)
Bacterial Classification
Bacteria can be classifieds according to :
1‐Macroscopic Morphology
2‐ Microscopic Morphology (Morphology, arrangement and Staining).
3. Cultural characteristics (aerobic, facultative anaerobic, anaerobic)
4. Biochemical reactions (ex. according to sugar fermentation reactions).
5. Antigenic structure and Serotyping.
6. Base composition of bacterial DNA (for example by assessing molecular
guanine and cytosine (GC) content).

45. How do organisms get their name?
the taxonomic ranks form the
basis for the organization of
bacteria. Linnaean taxonomy is
the system most familiar to
biologists.
It uses the formal ranks of
kingdom, phylum, class, order,
family, genus, and species

46. How do organisms get their name?
The scientific name of an organism is
classically performed of the last two ranks, i.e.
a combination of the generic (genus) name
followed by the species name, e.g.
Streptococcus salivarius (note that the
species name does not begin with a capital
letter). The name is usually written in italics
with the generic capital name abbreviated
(e.g. S. salivarius).
Example: Str. Salivarius
Family: Streptococaceae
Genus: Streptococcus
Species: Salivarius

47. How do organisms get their name?
When bacterial names are used adjectivally or collectively,
the names are not italicized and do not begin with a capital
letter (e.g. staphylococcal enzymes, lactobacilli).

48. Multiple‐choice questions
A‐Teichoic acid and lipoteichoic acid are present in the cell wall of:
1‐Gram positive and Gram negative bacteria.
2‐Gram negative bacteria.
3‐Gram positive.
B‐In Gram negative bacteria; endotoxin is the toxic properties of:
1‐core polysaccharide.
2‐The lipid A .
3‐an O‐specific side chain.

49. Q2/ Enumerate the Four criteria of Koch's postulates.