Bacteria cell structure.pptx

 Introduction to Clinical Bacteriology
 Bacteria Cell Structure
 Bacterial Classification

DIFFERENCE BETWEEN
PROKARYOTIC & EUKARYOTIC
CELL
Prokaryotic Cells Eukaryotic cells
small cells (< 5 mm) larger cells (> 10 mm)
always unicellular often multicellular
no nucleus or any membrane-bound
organelles
always have nucleus and other
membrane-bound organelles
DNA is circular, without proteins DNA is linear and associated with
proteins to form chromatin
ribosomes are small (70S) ribosomes are large (80S)
no cytoskeleton always has a cytoskeleton
cell division is by binary fission cell division is by mitosis or meiosis
reproduction is always asexual reproduction is asexual or sexual

Bacteriology is the study of bacteria.
A branch of microbiology dealing with the identification, stud
y and cultivation of bacteria and with their applications in
medicine, agriculture, industry, and biotechnology.
This subdivision of microbiology involves the identification,
classification, and characterization of bacterial species.
A person who studies bacteriology is a bacteriologist.

 Bacteria (singular: bacterium) constitute a large domain of
prokaryotic microorganisms.
 Typically a few micro-metres in length, bacteria have a number of
shapes, ranging from spheres to rods and spirals.
 Bacteria inhabit soil, water, acidic hot springs, radioactive waste,
and the deep portions of Earth's crust.
 The vast majority of the bacteria in the body are rendered
harmless by the protective effects of the immune system, and
some are beneficial.
 However, several species of bacteria are pathogenic and
cause infectious diseases

Average bacteria 0.5 - 2.0 um in diameter .
RBC is 7.5 um in diam.
Typically 0.1 - 20 m (with some exceptions)
Typical coccus: 1 m (e.g. Staphylococcus)
Typical short rod: 1 x 5 m (e.g. E. coli)

Bacteria are classified by shape into Following basic groups:
1. Cocci: are spherical or oval cells
2. Bacilli:(from baculus meaning rod) are rod shaped cells
3. Spirochete are flexuous spiral form
4. Spirilla are rigid spiral forms.
5. Actinomycetes are branching filamentous bacteria.
6. Mycoplasmas are bacteria that are cell wall deficient and hence do not
possess a stable morphology.

 Cocci may be oval, elongated, or flattened on one side.
 Cocci may remain attached after cell division.
 These group characteristics are often used to help identify certain cocci.

Cocci that remain in pairs after dividing are called
diplococci.
Cocci that remain in chains after dividing are called
streptococci.
Cocci that divide in two planes and remain in groups of
four are called tetrads.
Cocci that divide in three planes and remain in groups
cube like groups of eight are called sarcinae.
Cocci that divide in multiple planes and form grape like
clusters or sheets are called staphylococci.

Since bacilli only divide across their short axis there are
fewer groupings.
Bacillus is a shape (rod shaped) but there is also a genus
of bacteria with the name Bacillus

Most bacilli appear as single rods.
Diplobacilli appear in pairs after division.
Streptobacilli appear in chains after
division.
Some bacilli are so short and fat that
they look like cocci and are referred to as
coccobacilli.

Vibrios look like curved rods.
Spirilla have a helical shape and fairly rigid
bodies.
Spirochetes have a helical shape and flexible
bodies. Spirochetes move by means of axial
filaments, which look like flagella contained
beneath a flexible external sheath.
Spiral Bacteria

Stella are star-shaped.
Haloarcula, a genus of halophilic archaea, are
rectangular.

1. Cell Wall
2. Plasma Membrane
3. Capsule
4. Cytoplasm & Cytoplasmic Inclusions
5. Ribosomes
6. Bacterial DNA
7. Pili
8. Flagella
9. Spores

 Outer most component common to all bacteria ( except
Mycoplasma)
 Some bacteria have external future to cell wall e.g. capsule,
flagella, pili.
 Cell wall is multi-layered structure located external to the
cytoplasmic membrane
 Average thickness is 0.15-0.5 μm.
 It is composed of N-acetyl Muramic acid (NAM) and N-acetyl
Glucosamine (NAG) back bones cross linked with peptide chain
and pentaglycine bridge.

Components of cell wall of Gram negative bacteria
 1. Peptidoglycan
 2. Lipoprotein
 3. Phospholipid
 4. Lipopolysaccharide
Components of cell wall of Gram positive bacteria
 1. Peptidoglycan
 2. Teichoic acid

 Peptidoglycan is derived from “peptides “ & “Glycan” (sugar)
 It is also known as murine, mucoprotien
 Only found in bacteria cell wall
 It provide a rigid support , maintain the shape and allow the cell to with stand
the low osmotic pressure e.g. of water
 Peptidoglycane is a complex polymer consist of three parts
 A back bone
 Set of identical tetrapeptides
 Set of identical peptide cross bridge
 BACK BONE; composed of alternate NAM & NAG molecules
 TETRAPEPTIDE : L-alanine (1) , D-glutamate (2) , D-alanine (4)

 Gram-positive bacteria normally have cell walls that are thick and composed
primarily of peptidoglycan. Peptidoglycan in gram positive bacteria often contains
a peptide inter-bridge
 Most of the G +ve cell walls consist of considerable amount of teichoic acid and
teichuronic acid
 The teichoic acids are covalently connected to either the peptidoglycan itself or to
plasma membrane lipids; in the latter case they are called lipoteichoic acids.
 Teichoic acids appear to extend to the surface of the peptidoglycan, and, because
they are negatively charged, help give the gram-positive cell wall negative charge

 There are two type of teichoic acid :
 Wall teichoic acid
 Membrane teichoic acid
 They may be important in maintaining the structure of the wall.
 Teichoic acid constitute a major surface antigen of G+ve Bacteria
 Teichouronic acid are same in function just the difference of N-
acetyle mannosuronic acid and D-glucose Uronic acid

 Gram Negative cell wall is more complex then G+ve cell wall
 The thin peptidoglycan layer next to the plasma membrane and bounded
on either side by the periplasmic space may constitute not more than 5 to
10% of the wall weight.
 In E. coli it is about 2 nm thick and contains only one or two sheets of
peptidoglycan.
 1. The periplasmic space of gram-negative bacteria is also strikingly
different than that of gram-positive bacteria.

 It ranges in size from 1 nm to as great as 71 nm. Some recent
studies indicate that it may constitute about 20 to 40% of the total
cell volume, and it is usually 30 to 70 nm wide
 Some periplasmic proteins participate in nutrient acquisition—for
example, hydrolytic enzymes and transport proteins. Some
periplasmic proteins are involved in energy conservation.
 For example, the denitrifying bacteria, which convert nitrate to
nitrogen gas, and bacteria that use inorganic molecules as energy
sources (chemolithotrophs) have electron transport proteins in their
periplasm. Other periplasmic proteins are involved in peptidoglycan
synthesis and the modification of toxic compounds that could harm
the cell.

 Some bacteria, tubercle bacteria ( M. tuberculosis) have a cell wall
that contain large amount of waxes, known as mycolic acids
 Cell wall is composed of peptidoglycane and an external asymmetric
lipid bilayer
 The inner leaflets contain mycolic acid
 The outer leaflets contain other extractable lipids
 These hydrophobic structure renders these bacteria resistant to
many harsh chemicals including detergents and strong acids
 These organism are known as acid-fast bacteria

 The Archaea do not have cell walls like the Bacteria.
 Some have a simple S-layer often composed of glycoproteins.
 Some Archaea have a rigid cell wall composed of polysaccharides or
a peptidoglycan called pseudomurein.
 The pseudomurein differs from the peptidoglycan of bacteria by
having l-amino acids rather than d-amino acids and disaccharide
units with an a-1--3 rather than a-1--4 linkage.
 Archaea that have a pseudomurein cell wall are gram-positive

 The mycoplasmas are cell wall-lacking bacteria containing no
peptidoglycan.
 There are also wall-less Archaea, but they have been less well
studied. Genomic analysis places the mycoplasmas close to the
gram-positive bacteria from which they may have been derived.
 Mycoplasmas lack a target for cell wall-inhibiting antimicrobial
agents (eg, penicillins and cephalosporins) and are therefore
resistant to these drugs.
 Some, such as Mycoplasma pneumoniae, an agent of pneumonia,
contain sterols in their membranes.

 Some prokaryotes have a layer of material lying outside the cell wall.
 This layer has different names depending on its characteristics. When the layer is
well organized and not easily washed off, it is called a capsule.
 It is called a slime layer when it is a zone of diffuse, unorganized material that is
removed easily. When the layer consists of a network of polysaccharides extending
from the surface of the cell, it is referred to as the glycocalyx
 Many procaryotes have a regularly structured layer called an S-layer on their
surface. In bacteria, the S-layer is external to the cell wall.

 In archaea, the S-layer may be the only wall structure outside the
plasma membrane. The S-layer has a pattern something like floor
tiles and is composed of protein or glycoprotein
 In gram-negative bacteria the S-layer adheres directly to the outer
membrane; it is associated with the peptidoglycan surface in
grampositive bacteria.
 It may protect the cell against ion and pH fluctuations, osmotic
stress, enzymes
 The S-layer also helps maintain the shape and envelope rigidity of
some cells.
 It can promote cell adhesion to surfaces.
 Finally, the S-layer seems to protect some bacterial pathogens
against host defenses, thus contributing to their virulence

 Most motile prokaryotes move by use of flagella (s., flagellum), threadlike
locomotor appendages extending outward from the plasma membrane and
cell wall.
 Flagella are long whipe like appendages that move bacteria toward
nutrients and other attractants
 Bacterial flagella are slender, rigid structures, about 20 nm across and up
to 15 or 20 nm long.
 Flagella are so thin they cannot be observed directly with a bright-field
microscope, but must be stained with special techniques designed to
increase their thickness.

Bacterial species often differ distinctively in their patterns
of flagella distribution and these patterns are useful in
identifying bacteria.
 Monotrichous bacteria (trichous means hair) have one flagellum; if
it is located at an end, it is said to be a polar flagellum
 Amphitrichous bacteria (amphi means on both sides) have a single
flagellum at each pole.
 lophotrichous bacteria (lopho means tuft) have a cluster of flagella
at one or both ends.
 Flagella are spread fairly evenly over the whole surface of
peritrichous (peri means around) bacteria

External Anatomical Structures
-- Bacterial Flagella
Arrangements
Monotrichous
Lophotrichous
Amphitrichous
Peritrichous

 Bacterial flagellum is composed of three parts.
 (1) The longest and most obvious portion is the flagellar filament, which extends
from the cell surface to the tip.
 (2) A basal body is embedded in the cell
 (3) a short, curved segment, the flagellar hook, links the filament to its basal
body and acts as a flexible coupling.
 The filament is a hollow, rigid cylinder constructed of subunits of the
protein flagellin, which ranges in molecular weight from 30,000 to
60,000 daltons, depending on the bacterial species.
 The filament ends with a capping protein.
 Some bacteria have sheaths surrounding their flagella.

 Many gram-negative bacteria possess rigid surface appendages
called pili (L “hairs”) or fimbriae (L “fringes”).
 They are shorter and finer than flagella; similar to flagella,
 They are composed of structural protein subunits termed pilins.
 Some pili contain a single type of pilin, others more than one.
 Minor proteins termed adhesins are located at the tips of pili and
are responsible for the attachment properties.
 Two classes can be distinguished:
 ordinary pili, which play a role in the adherence of symbiotic and pathogenic
bacteria to host cells.
 sex pili, which are responsible for the attachment of donor and recipient cells in
bacterial conjugation

 The bacterial cell membrane, also called the cytoplasmic membrane, is
visible in electron micrographs of thin sections
 It is a typical “unit membrane” composed of phospholipids and upward
of 200 different kinds of proteins.
 Proteins account for approximately 70% of the mass of the membrane,
which is a considerably higher proportion than that of mammalian cell
membranes
 The cell membranes of the Archaea differ from those of the Bacteria.
Some Archaeal cell membranes contain unique lipids, isoprenoids,
rather than fatty acids, linked to glycerol by ether rather than an ester
linkage.
 Some of these lipids have no phosphate groups, and therefore, they are
not phospholipids.

 The major functions of the cytoplasmic membrane are
1. Selective permeability and transport of solutes
2. Electron transport and oxidative phosphorylation in aerobic species
3. Excretion of hydrolytic exoenzymes
4. Bearing the enzymes and carrier molecules that function in the biosynthesis of
DNA, cell wall polymers, and membrane lipids
5. Bearing the receptors and other proteins.
 At least 50% of the cytoplasmic membrane must be in the semifluid state for cell
growth to occur.

 The cytoplasm have two distinct areas
 An amorphous matrix that contain ribosomes nutrient granules, metabolites
and plasmids
 An inner , nucleoid region composed of DNA
 The cytoplasmic matrix is the substance in which the nucleoid,
ribosomes, and inclusion bodies are suspended.
 It lacks organelles bound by lipid bilayers (often called unit
membranes), and is largely water (about 70% of bacterial mass is
water).
 The plasma membrane and everything within is called the
protoplast

 Ribosomes are very complex structures made of both protein and
ribonucleic acid (RNA).
 They are the site of protein synthesis.
 Procaryotic ribosomes are called 70S ribosomes.
 The S in 70S and similar values stands for Svedberg unit. This is the unit
of the sedimentation coefficient, a measure of the sedimentation velocity
in a centrifuge; the faster a particle travels when centrifuged, the greater
its Svedberg value or sedimentation coefficient.
 The sedimentation coefficient is a function of a particle’s molecular
weight, volume, and shape

 The cytoplasm contain several different types of granules that serve
as a storage areas for nutrient and stain.
 cytoplasm—for example, polyphosphate granules, cyanophycin
granules, and some glycogen granules.
 Other inclusion bodies are enclosed by a shell about 2.0 to 4.0 nm
thick, which is single-layered and may consist of proteins or a
membranous structure composed of proteins and phospholipids.

 Prokaryotes lack a membrane-delimited nucleus.
 The prokaryotic chromosome is located in an irregularly shaped region
called the nucleoid (other names are also used: the nuclear body,
chromatin body, nuclear region).
 Nucleoid contain no nuclear membrane, no nucleolus, no mitotic spindle
and no histones .
 The bacterial DNA do not have Intrones

 Usually prokaryotes contain a single circle of double-stranded
deoxyribonucleic acid (DNA), but some have a linear DNA chromosome
and some, such as Vibrio cholerae and Borrelia burgdorferi (the
causative agents of cholera and Lyme disease, respectively), have more
than one chromosome
 It is possible to isolate pure nucleoids.
 Chemical analysis of purified nucleoids reveals that they are composed
of about 60% DNA, 30% RNA, and 10% protein by weight

 In addition to the genetic material present in the nucleoid, many prokaryotes
(and some yeasts and other fungi) contain extrachromosomal DNA molecules
called plasmids.
 Numerous different plasmids within a single species have been identified. For
instance, B. burgdorferi, carries12 linear and 9 circular plasmids.
 Plasmids are small, double-stranded DNA molecules that can exist
independently of the chromosome. Both circular and linear plasmids have been
documented, but most known plasmids are circular.
 Linear plasmids possess special structures or sequences at their ends to prevent
their degradation and to permit their replication.
 Plasmids have relatively few genes, generally less than 30.

 Plasmids are able to replicate autonomously. Single-copy plasmids
produce only one copy per host cell. Multicopy plasmids may be
present at concentrations of 40 or more per cell.
 Some plasmids are able to integrate into the chromosome and are
thus replicated with the chromosome. Such plasmids are called
episomes.
 Plasmids are inherited stably during cell division, but they are not
always equally apportioned into daughter cells and sometimes are
lost. The loss of a plasmid is called curing

 Members of several bacterial genera are capable of forming endospores .
 The two most common are gram-positive rods: the obligately aerobic genus Bacillus
and the obligately anaerobic genus Clostridium.
 The other bacteria known to form endospores are Thermoactinomyces,
Sporolactobacillus, Sporosarcina, Sporotomaculum, Sporomusa, and
Sporohalobacter spp.
 Each cell forms a single internal spore that is liberated when the mother cell
undergoes autolysis.
 The spore is a resting cell, highly resistant to desiccation, heat, and chemical
agents; when returned to favorable nutritional conditions and activated the spore
germinates to produce a single vegetative cell.

SPORULATION
 The sporulation process begins when nutritional conditions become
unfavorable, near depletion of the nitrogen or carbon source (or
both) being the most significant factor.
 Sporulation occurs massively in cultures that have terminated
exponential growth as a result of this near depletion.

1. Core—The core is the spore protoplast. It contains a complete
nucleus (chromosome), all of the components of the protein-
synthesizing apparatus, and an energy-generating system based on
glycolysis
2. Spore wall—The innermost layer surrounding the inner spore
membrane is called the spore wall. It contains normal peptidoglycan
and becomes the cell wall of the germinating vegetative cell.
3. Cortex—The cortex is the thickest layer of the spore envelope.

 4. Coat—The coat is composed of a keratin-like protein containing
many intramolecular disulfide bonds. The impermeability of this
layer confers on spores their relative resistance to antibacterial
chemical agents.
 5. Exosporium—The exosporium is composed of proteins, lipids, and
carbohydrates. It consists of a paracrystalline basal layer and a
hairlike outer region. The function of the exosporium is unclear.
Spores of some Bacillus species (eg, B anthracis and B cereus)
possess an exosporium, but other species (eg, B atrophaeus) have
spores that lack this structure.
 C. 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 they have rested for
several days or are first activated in a nutritionally rich medium by one
or another agent that damages the spore coat.
 Among the agents that can overcome spore dormancy are heat,
abrasion, acidity, and compounds containing free sulfhydryl groups.
 2. Initiation—After activation, a spore will initiate germination if the
environmental conditions are favorable.
 3. Outgrowth—Degradation of the cortex and outer layers results in the
emergence of a new vegetative cell consisting of the spore protoplast
with its surrounding wall. A period of active biosynthesis follows; this
period, which terminates in cell division, is called outgrowth. Outgrowth
requires a supply of all nutrients essential for cell growth..

 The β1→4 linkage of the peptidoglycan backbone is hydrolyzed by
the enzyme lysozyme, which is found in animal secretions (tears,
saliva, nasal secretions) as well as in egg white.
 Gram-positive bacteria treated with lysozyme in low-osmotic-
strength media lyse; if the osmotic strength of the medium is
raised to balance the internal osmotic pressure of the cell, free
spherical bodies called protoplasts are liberated.

The outer membrane of the gram-negative cell wall
prevents access of lysozyme unless disrupted by an agent
such as ethylene-diaminetetra acetic acid (EDTA), a
compound that chelates divalent cations; in osmotically
protected media, cells treated with EDTA-lysozyme form
spheroplasts that still possess remnants of the complex
gram-negative wall, including the outer membrane.

 Bacteria themselves possess a number of autolysins, hydrolytic
enzymes that attack peptidoglycan, including muramidases,
glucosaminidases, endopeptidases, and carboxypeptidases.
 These enzymes catalyze the turnover or degradation of
peptidoglycan in bacteria.
 These enzymes presumably participate in cell wall growth and
turnover and in cell separation, but their activity is most apparent
during the dissolution of dead cells (autolysis).

Bacteria cell structure.pptx

More Related Content

What's hot

Similar to Bacteria cell structure.pptx

Recently uploaded

Bacteria cell structure.pptx