Transcript Lecture 3

Functional Anatomy of Prokaryotic
Cells
1
All living cells can be classified into
two groups based on certain structural
& functional characteristics
Prokaryotes •
Eukaryotes •
•
They are chemically similar in the
sense that they both contain
nucleic acids
proteins
lipids
carbohydrates
The distinguishing characteristic of
prokaryotes & eukaryotes
* 0.2-2.0 microm •
•
*DNA is not enclosed within a •
membrane (singularly arranged
chromosome)
Proka.
*DNA is not associated with •
histones=special chromosomal
proteins found in euk
•
*no membrane-enclosed •
organelles
•
*cell wall almost always •
contain the complex polysaccharide
peptidoglycan
•
*divided by binary fission(DNA •
is copied & the cell splits into two cells
The distinguishing characteristic of
prokaryotes & eukaryotes
*10-100microm. •
•
*DNA is found in cells nucleus •
which is separated from the cytoplasm
by nuclear membrane (DNA is found in
multiple chromosomes)
•
*DNA is associated with •
histones
Euka.
*the have a number of membrane- •
enclosed organelles(mitochondria ,
endoplasmic reticulum Golgi complex
lysosomes)
•
*cell wall is chemically simple •
•
*cell division usually involves •
mitosis
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EUKARYOTES
PROKARYOTES
BACTERIA ARCHAEA
9
BACTERIA
Naming and Classifying Microorganisms
The system for nomenclature for microorganisms •
The scientific name is binomial •
The First is the genus name
The Second is the species name
The first letter of the genus name is always
capitilized
Staphylococcus (genus) aureus (species)
Both are underlined or italicized
Staphylococcus aureus
Staphylococcus aureus
Identification of bacteria
Thousands of bacteria species are differentiated by
many factors
including:
**morphology (shape , size & arrangement) •
**Chemical composition (staining)
**Nutritional requirements
**Biochemical activities
**Source of energy
•
Morphology
Size -- Shape -- & Arrangement
Size = 0.2 – 2.0 micrometer in
diameter
2.0 -- 8.0 micrometer in
length
Bacterial shapes are determined by
heredity
Shapes & Arrangements of
Bacteria
cocci
Coccus=spherical
=round or oval
•
Diploccoci=pairs •
Streptococci=chainlike •
Staphylococci=groups
(grapelike)
•
Bacilli
Bacilli= rode shape •
mostly Single
Diplobacilli=pairs •
Streptobacolli=chais •
Coccobacilli=oval •
spiral
Have one or more •
twists----never
straight
Vibrios=curved rods •
Spirilla=helical •
Spirochetes=helical •
& flexible
Structure of Bacteria
Essential structures
cell wall
cell membrane
Cytoplasm & nuclear material
Particular structures
capsule
flagella
pili
spore
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STRUCTURE OF BACTERIAL CELL
19
19
Structures
structures external to the cell wall
cell wall itself
structures internal to the cell wall
structures external to the cell
wall
glycocalyx (capsule)
flagella
axial filaments
fimbriae
pili
GLYCOCALYX
Glycocalyx=sugar •
coat=sub.that surround
cells=sticky=external to cell
wall
Polysaccharide , •
polypeptide or both
If attached to cell wall •
=capsule (well defined)
or slim layer(not defined)
GLYCOCALYX
Capsule or slime layer
• Functions:
– Help adherence & attachment
of bacterial cells to surfaces.
– Provide nutrients
– Protect bacterial cells against dehydration
– Increase virulence of bacteria
Protect the pathogenic bacteria.
From phagocytosis by host
The degree of which
WBC
bac. Cause disease
• 23.
23
Streptococcus pneumoniae
pneumonia
respiratory tract
FLAGELLA
Some bacteria are motile •
Locomotory organelles- •
flagella=long filamentous
appendages •
External to cell wall
25
Flagellar arrangements outside bacterial cell
Atrichous –lack flagella
26
Monotrichous –
single flagellum at
one end
27
Lophotrichous-2 or
more arising from
one end of bacterial
cell
Amphitrichous- flagella at both
end of bacterial
Peritrichous – Flagella
distributed over the entire
surface, low
motility
Motility=is the ability of bac. to move
itself
one direction
different directions
waves
toward a favorable environment
or
away from an adverse conditions
chemotaxis=away from chemicals
light=phototaxis
Advantages of flagella
Identification of Bacteria •
H-antigen = flagellar protein is •
useful for distinguish
variations within species
Motility of bacteria
Axial filaments
similar to flagellum •
=bundles of fibrils that arise at the •
end of bacterial cell
**Spiral motion •
**Snake-like movement •
–spirochetes have unique
structure & motility
30
Pili (fimbriae)
hair-like projections of the cell•
(shorter and thinner than flagella)
Occur at the poles or can evenly distributed on
bacterial cell
Fibriae are involve in bacterial attachment to surfaces and
resistance to phagocytosis === cause disease
Neisseria gonorrhoeae
gonorrhea
31
Pili
Chemical nature is pilin
bacterial conjugation
Sex pili effect the transfer of
conjugative plasmids
32
FIMBRIE
FLAGELLA
SEX PILI
EXTRACELLULAR APPENDAGES
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STRUCTURE OF BACTERIAL CELL
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34
Composition &
structure of cell wall
Bacterial cell wall
All prokaryotes have cell wall •
The cell wall of bacterial cell is •
Complex •
Surround the fragile plasma membrane •
(cytoplasmic)
Protect the interior of cell •
The major functions of cell wall
Prevent bacterial cells from rupturing,
when water pressure inside the cell is
greater than that outside the cell , so
it is essential for bacterial viability
Countering the effects of osmotic
pressure
Providing a rigid platform for surface
appendages- flagella, fimbriae, and pili
all originate from the wall and extend
beyond it
Cell wall major functions
Site of action of antibiotics, the most
important one
Resistance of Antibiotics
• Shape of bacteria
Functions of cell wall
The chemical composition of cell wall
is used to differentiate major types of
bacteria.
Be the sites of major antigenic
determinants of the cell surface
Provide the immunological distinction
among bacteria
Bacterial cell wall is composed of •
macromolecular net work =
peptidoglycan
Peptidoglycan = peptide + glycan
Peptidoglycan consists of repeating
disaccharide attached by polypeptides ,
that surrounds & protects bacterial cell
Disaccharide portion
is mad up of
Monosaccharides =
N-acetylglucosamine
(NAG)
&
N-acetylmuramic
acid=
(NAM)
4/6/2016
CELL WALL
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Alternating
(NAG) &( NAM)
molecules are
linked in rows
to from a
carbohydrate
backbone
(glycan portion )
Adjacent rows are
linked by
polypeptides
CELL WALL
(peptide portion)
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4/6/2016
Penicillin interferes
with final linking
of the
peptidoglycan
rows by peptide
=bac.cell wall is
weakened & the
cell undergoes
lysis
= this destruction
caused by
rupture of the
CELL WALL
plasma
membrane & the
43
loss of cytoplasm
43
Gram positive bacteria
cell wall consists of many layers of
peptidiglycan forming a thick , rigid structure
Cell wall of Gram positive bac. Contain •
Teichoic acids= consist primarily of •
•
an alcohol (glycerol or ribitol) •
& •
phosphate •
Teichoic acid classes
Wall teichoic acid =
linked to the
peptidoglycan
Lipoteichoic acid=
spans the
peptidoglycan layer
& is linked to the
plasma membrane
Special components of Gram
positive cell wall
Teichoic acid
SPA / M POTEIN
46
Teichoic acid = •
Regulate the movement of cations (+ve •
ions) into & out of the cell
Assume in cell growth •
Provide wall s antigenic specificity = •
diagnosis
Gram negative bacteria cell wall
Consist of one layer of peptidoglycan •
& •
an outer membrane •
Do not contain teichoic acid •
the peptidoglycan is bonded to •
lipoproteins
(=lipids linked to proteins) in the •
outer membrane
The outer membrane of Gm.-ve bac, consists
of
Lipopolysaccharides
lipoproteins •
& •
phospholipids •
•
Lipopolysaccharides
O
polysaccharides
antigen
Lipid portion
Lipid A
endotoxin
Porin = is a proteins in the outer
membrane which is important in
the permeability of outer
membrane
CELL WALL OF G+VE AND G-VE BACT.
GRAM STAIN TECHNIQUE
CELL WALL STRUCTURE AND GRAM STAIN
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ATYPICAL CELL WALLS
1- No or very little cell wall material: Mycoplasma
= are the smallest bacteria that can & reproduce
outside living cell (sterols in the plasma membranes for
protection)
2- Archaea: unusual
wall-- No peptidoglycan, , proteins and
polysaccharides.
3- Acid-fast cell walls: contain high constration (60%)
of
Waxy material outside the peptidoglycan. = Mycolic acids prevent
uptake of stains.
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Damage to the cell wall
Chemicals that damage bact. Cell wall often do not harm the cells
of an animal host .Why??
When bacteria are treated with
1) enzymes that are lytic for the cell wall e.g. lysozyme
(tears,mucus, saliva)
Active on major cell wall components of most Gram +ve bact.
**back bone disaccharide
wall-less cell (protoplast)
When Gram –ve bact. Treated with lysozyme cell wall is not
destroyed to the same extant as in Gram +ve bact. Why ??
(outer membrane) (spheroplast)
55
Effect of "lysozyme", which is found •
naturally in tears, mucus, and saliva.
-Gram positives are most susceptible and
typically they burst (lyse) or, in favorable
environments, they may form "protoplasts",
which have no cell wall.
-Gram negatives are less susceptible and
some of the cell wall material remains
(spheroplasts)--> Can only survive in
.favorable conditions as they are weak
Damage to the cell wall
2) antibiotics that interfere with biosynthesis of peptidoglycan,
wall-less bacteria are often produced.
antibiotics that damage bact. Cell wall often do not harm the
cells of an animal host .Why??
58
STRUCTURE OF BACTERIAL CELL
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Structures internal to the cell wall
Structures internal to the cell wall
Plasma or cytoplasmic
membrane
**Is a thin structure lying inside the cell wall & •
enclosing the cytoplasm
**consist primarily of phospholipids & proteins •
Functions of Plasma
membrane
Selective permeability = certain molecules &
ions pass through the membrane , but others
prevented from passing through it
•
Breakdown of nutrients and the production of •
energy ( contain enzymes catalyzing the
chemical reaction)
Some antibiotics and antibacterial agents kill •
bacteria by attacking the plasma membrane
Damage of plasma membrane
Many antibiotics have effect on plasma •
membrane
Polymyxins = disrupting phospholipids of •
the plasma membrane
Alcohols & ammonium compounds = •
used as
disinfectants
Structures within the bacterial
cell
• Cytoplasm: thick
aqueous (80% water)
semitransparent.
• Contains organic
molecules and inorganic
ions. Proteins(enzymes) ,
carbohydrates , & lipids
• The major structures
in the cytoplasm are:
• Nucleoid,
ribosomes,
inclusions
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The major structures in the cytoplasm
are:
Nucleoid,= nuclear area •
containing DNA
Ribosomes •
Inclusions = reserve •
deposits
NUCLEAR MATERIAL
Plasmids:
.
Single, long, double stranded circular DNA=bacterial
chromosome.
Carry all the genetic information required for cell structure
& function
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extra-chromosomal DNA •
PLASMID
Small,circular,doubl-stranded •
DNA .not connected to bact.
Chromosome, replicate
independently
May be gained or lost. Without •
harming bact.
Can be transfer from one bact. •
To other (biotechnology)
Plasmids:
Cary genes for: )5-100 genes) •
antibiotic resistance, •
.
tolerance to toxic metals, •
production of toxins and •
synthesis of enzymes
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Nuclear
material
• No
nuclear membrane,
absence of nucleoli, hence known as nucleic
material or nucleoid,
one to few per bacterium.
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Ribosomes
Sites of protein synthesis
Composed of two subunits made of protein and
ribosomal RNA.
Prokaryotic ribosomes are 70S while
Eukaryotic ribosomes are 80S.
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 Erythromycin and chloramphenicol attach to 50 S subunit
 Streptomycin and gentamicin attach to 30 S subunit and inhibit protein
synthesis.
Bacterial cell can be killed by antibiotic while eukaryotic
cell remains unaffected. Why???
70
•
Inclusions
Several kinds of reserve deposits
within the cytoplasm
Cells may accumulate certain •
nutrients when they are plentiful &
use them when the environment is
deficient
Their number depend on bact.
Species == identification
•
•
Inclusions
• Reserve deposits
• Metachromatic granules.
• Polysaccharide granules = carbohydrate
• Lipid inclusions = lipid storage material
• Sulphur granules = energy server
• Carboxyzomes = enzymes ** photosynthesis
• Gas Vacuoles
• Magnetosomes
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Inclusions
Metachromatic granules =large = •
inclusions
some time stain red with blue dye •
have diagnostic significance
=stores inorganic phosphate
Corynebacterium diphtheriae
Endospores (spores)
Resting structures •
Clostridium= tetanus – gas gangrene – •
food poisoning
Bacillus = anthrax •
Highly durable dehydrated cells with thick •
walls & additional layers which formed
internal to the bact. cell membrane
Endospores when released into •
environment they survive
•
-- extreme heat •
•
--lack of water •
•
--exposure to many toxic chemicals & •
radiation
Sporulation = sporogenesis •
formation of endospore •
(endospre forming bact.) •
This occur when nutrient •
(carbon , nitrogen source )
becomes unavailable or scarce
Germination = formation of •
vegetative form
Endospores
(spores)
Identification 
of Bacteria
Pathogenesis 
Resistance 
77
One vegetative cell
endospore
Sporulation
Single endospore germination
cell
single •
one vegetative •
Not a means of reproduction •
protection •
•
Endospores are clinically important •
Food industry •
Resist heating •
Freezing •
Desiccation •
Use of chemicals & radiation •
Some bact. Produce toxins •
BACILLUS ANTHRAX
BACTERIAL
SPORES
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First Term Exam.
Good Luck