Download Chapter 9: Structure of Bacteria

BIOL 2261
CHARACTERISTICS FEATURS OF
BACTERIAL CELL
CHAPTER 9
© Thomas Deerinck, NCMIR / Science Photo Library
Types of Cells
Two major classes: eukaryotes & prokaryotes.
Differences: the materials making up the nucleus of
eukaryotic cells are separated from the rest of the cell
by the nuclear membrane, whereas in prokaryotic cells
these materials are not separated.
• All animals and plant cells are eukaryotic including
fungi. Bacteria, cyanobacteria and the mycoplasmas are
prokaryotic.
Size, Shape, and Arrangement of
Bacterial cells
Cocci (s., coccus) – spheres
–diplococci (s., diplococcus) – pairs
–streptococci – chains
–staphylococci – grape-like clusters
–tetrads – 4 cocci in a square
–sarcinae – cubic configuration of 8
cocci
……Size, Shape, and Arrangement
Bacilli (s., bacillus): – rods
– coccobacilli – very short rods
– vibrios – resemble rods, comma shaped
• spirilla (s., spirillum) – rigid helices
• spirochetes – flexible helices
• mycelium – network of long, multinucleate
filaments Check on line lab Manual for
Bacterial shapes)
……Size, Shape, and
Arrangement
– Sizes:
• 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)
• Barely within the best resolution of a
good compound light microscope
Bacterial Shapes
Cell Structure
of Procaryotes
Prokaryotic cells
The constituents of a typical bacterium are as follows:
• Bacterial Cell Wall and Capsule – bacteria are
•
•
•
surrounded by a cell wall, which not only contains
polysaccharide but also contains protein and lipid.
In some bacteria, the cell wall is surrounded by the
capsule.
The cell wall and capsule provide shape and form to
the bacterium and also acts as a physical barrier
between the bacterium and its environment.
Nucleoids – in bacteria the nuclear material is
concentrated in a region called the nucleoid within
the cytoplasm.
Typical Prokaryotic Cell
A typical Bacterial Cell
….Cell Structure
• There is no membrane-bound nucleus in
•
•
prokaryotes.
Instead the DNA is located within a
specialized region of the cytoplasm of the cell
called the nucleoid region.
There is no nuclear membrane surrounding
the nucleoid.
• Bacterial flagella – many bacteria
possess one or more flagella for
locomotion.
Bacterial Cell Walls
Bacterial Cell Wall:
• rigid structure that lies just outside the
plasma membrane (detail to continue)
• The cell wall is a complex meshwork
structure composed of several parts.
…..Bacterial Cell Walls
• The primary structure of the cell wall is
peptidoglycan which is composed of
repeating sugar molecules.
– N-acetyl glucosamine (NAG)
– N-acetyl muramic acid (NAM)
• The meshwork is held together with
small peptide chains (Fig 9.3).
Functions of Cell Wall
• provides characteristic shape to cell
• The bacterial cell wall is a protective
barrier against:
– Osmotic pressure changes
– Other environmental stresses
• may also contribute to pathogenicity
• very few procaryotes lack cell walls
• The cell wall is different in Gram-
positive and Gram-negative bacteria.
Gram stain-Cell Walls of
Bacteria
Gram Staining developed by Gram in
1884:
• bacteria are divided into two major
groups based on the response to gramstain procedure
– gram-positive bacteria stain purple
(positive-purple-pp)
– gram-negative bacteria stain pink
• staining reaction due to cell wall
structure
Gram-Positive Cell Walls
Component of Cell Wall
• Gram positive bacteria composed primarily
of peptidoglycan/murein
• Peptidoglycan are polymers which contains
amino acids: N-acetylglucosamine and Nacetylmuramic acid and several different
amino acids
• Walls contain teichoic acid ( polymers of
glycerol or ribitol joined by phosphate groups)
Gram-Positive Cell Walls
• Teichoic Acid
– There are two forms
• Wall teichoic acids – go part way through
the wall.
• Lipoteichoic acids – go completely through
the wall and link to the plasma membrane.
– Both forms protrude above the wall, which
gives the bacterial cell a negative charge.
Gram Positive and Gram
negative
..Gram-Positive Cell Walls
• M Protein
– This is a virulence factor.
– It protrudes from the cell wall.
– It is required for infection.
– It is highly susceptible to mutations
..Gram-Positive Cell Walls
• Mycolic Acid
– This is found in the Mycobacterium
species.
– It consists of a waxy lipid incorporated into
the cell wall.
– It makes cells extremely resistant to
environmental stress.
– It acts as a barrier against antibiotics and
host defenses.
..Gram-Positive Cell Walls
• The periplasmic space lies between
plasma membrane and cell wall and is
smaller than that of gram-negative
bacteria
• as such periplasm has relatively few
proteins
• enzymes secreted by gram-positive
bacteria are called exoenzymes
Gram Positive Cell Wall
Gram-Negative Cell Walls
• consist of a thin layer of peptidoglycan
surrounded by an outer membrane
• outer membrane composed of lipids,
lipoproteins, and lipopolysaccharide
(LPS)
• Lipoprotein molecules fasten the outer
membrane to the peptidoglycan layer.
• no teichoic acids
….Gram-Negative Cell Walls
• The outer membrane of Gram-negative
bacteria has a unique outer layer.
– It is composed of lipopolysaccharides
instead of the standard phospholipid
molecules.
• It serves as a major barrier to the
outside world for the Gram-negative
cell.
…..Gram Negative
• more complex than gram-positive walls
• periplasmic space differs from that in
gram-positive cells (occupies larger
space)
– may constitute 20-40% of cell volume
– many enzymes present in periplasm
Gram Negative Cell Wall
Differences between a gram
positive and gram negative cell
wall.
Acid-fast Bacteria
Acid-fast Cell Walls
– Many genera in the “High GC grampositive” bacterial group contain mycolic
acids, embedded in the peptidoglycan .
– Mycolic acids are a class of waxy,
extremely hydrophobic lipids.
– Certain genera contain very large
amounts of this lipid, and are difficult to
gram stain.
– These genera may be identified by the
“acid-fast” staining technique.
– Includes Mycobacterium.
Wall deficient Organisms
Mycoplasmas
Bacteria
that are naturally have no
cell walls
Includes Mycoplasma and
Ureaplasma
Archaea :
Have archaea cell walls with no
peptidoglycan
Cell Structures outside the
Bacterial cell wall— External
There are five structures that can be found outside the cell wall.
No bacterium has all five of these structures
Capsules, Slime Layers, and
S-Layers
Layers of material lying outside the cell
wall
– capsules
• usually composed of polysaccharides
• well organized and not easily removed from cell
– slime layers
• similar to capsules except diffuse, unorganized
and easily removed.
• a capsule or slime layer composed of
polysaccharides can also be referred to as a
glycocalyx
…Glycocalyx-Slime layer &
Capsule
….Glycocalyx
• The glycocalyx is a sticky substance
composed of polypeptides, polysaccharides
or both.
• It is produced in the cytoplasm and secreted
to the outer part of the cell wall.
• It provides a protective element against
environmental stress.
• It can be used for nutrition.
S-layers:
S-layers:
• If glycocalyx is loosely attached to the wall, it is
•
called a slime layer.
If adhered tightly to the wall, it is called a capsule.
– regularly structured layers of protein or
glycoprotein.
Clinical Significance of Glycocalyx:
Adherence is a major part of infection (staying in),
especially in respiratory and urinary tract
infections.
• The glycocalyx is a primary factor of adherence.
Functions of Capsules, Slime
Layers, and S-layers
• protection from host defenses (e.g.,
phagocytosis)
• protection from harsh environmental
conditions (e.g., desiccation) ,
chemicals or osmotic stress
• attachment to surfaces
• facilitate motility
– nutrient Storage
Flagella
• In bacteria the flagellum is a hair-like
•
•
projection used for movement by rotating
around its axis. Flagella are only used for
movement.
Sex pilli are projections that transfer DNA
material from one bacterium to another's
plasmid.
Pilli helps bacteria to fasten onto surfaces such
as host membranes.
…FLAGELLA CONFIGURATIONS
Different species have different flagella arrangements
( types
of flagella Ref pg 93).
•Monotrichous – one flagellum located at the end
of the cell
•Amphitrichous – two flagella, one at each end
of the cell
•Lophotrichous – two or more flagella located at
the same end of the cell
•Peritrichous – flagella surround the entire cell.
….Function & Structure of
Flagella
•
Function:
–Mobility
–Almost all motile bacteria are motile
by means of flagella
–Motile vs. non motile bacteria.
Structure:
A flagella consists of the following
three parts:
– Filament
– Hook
– Basal body
– Filament composed of the protein flagellin
– Hook & Rotor Assembly & Permits
rotational "spinning" movement
Chemotaxis
• movement towards a chemical
attractant/light or away from a chemical
repellent/light
• concentrations of chemical attractants
and chemical repellents detected by
chemoreceptors on surfaces of cells
Pili and Fimbriae
Fimbriae (sing., fimbria)
– short, thin, hairlike, proteinaceous
appendages up to 1,000/cell
– mediate attachment to surfaces
sex pili/Conjugating pilli (s., pilus):
– similar to fimbriae except longer, thicker,
and less numerous (1-10/cell)
– required for mating
FIMBRIAE AND PILI –Axial
filaments
Panel a: © Thomas Deerinck, NCMIR / Science Photo Library; Panel b: © Dennis Kunkel
Microbiology: A Clinical Approach © Garland Science
Axial Filaments — Attachment
Homework
1.List the clinical significance of Bacterial cell
wall ( positive and negative)
( Pg 160)?
2. List the differences between a gram
positive and gram negative cell wall.
STRUCTURES INSIDE THE
BACTERIAL CELL WALL
There are six major structures found inside the
bacterial cell well:
•Plasma membrane
•Nuclear region
•Plasmids
•Ribosomes
•Inclusion bodies
•Endospores
Procaryotic Cell Membranes
Cell Membranes:
• membranes are an absolute
requirement for all living organisms.
• plasma membrane encompasses the
cytoplasm
• some procaryotes also have internal
membrane systems
Functions of the Plasma
Membrane
• separation of cell from its environment
• selectively permeable barrier
•
– some molecules are allowed to pass into or
out of the cell
– transport systems aid in movement of
molecules
detection of and response to chemicals in
surroundings with the aid of special receptor
molecules in the membrane
Cell Structures — Membrane
Fluid Mosaic Model of Membrane
Structure
…..Plasma membrane
…PLASMA MEMBRANE
…Phospholipid layer
• polar ends
– interact with water
– hydrophillic
• nonpolar ends
– insoluble in water
– hydrophobic
Phospholipid layer
Membrane Proteins
Peripheral proteins:
– loosely associated with the membrane and
easily removed
Integral proteins
– embedded within the membrane and not
easily removed
• ATP production occurs at the plasma
membrane.
• The proteins associated with electron
transport are located in the plasma
membrane
TYPES OF MEMBRANE TRANSPORT
The plasma membrane regulates what enters the
cell cytoplasm and what does not.
There are three types of membrane transport:
•Osmosis- water chases the concentration of
solutes (higher to lower concentration)
•Passive transport: 2 types:
-Simple diffusion- does not require ATP (higher
to lower concentration)
- Facilitated diffusion- does not require ATP but
uses carrier proteins called permease proteins.
•Active transport-Active transport requires ATP.
•( Against a concentration gradient)
Internal Structures
Cytoplamic Matrix:
• Cytoplasm contains the nucleoid, ribosomes
and inclusion bodies
• lacks organelles bound by unit membranes
• composed largely of water
• is a major part of the protoplasm (the
plasma membrane and everything within)
..Cytoplasmic Matrix
–Viscous aqueous suspension of proteins,
nucleic acid, dissolved organic
compounds, mineral salts
–Network of protein fibers similar to the
eukaryotic cytoskeleton.
Nuclear Region/The Nucleoid
Nucleoid:
• irregularly shaped region
• location of chromosome
– usually 1/cell
• not membrane-bound
The Procaryotic Chromosome
The Chromosomes:
• usually a closed circular, doublestranded DNA molecule
• looped and coiled extensively
PLASMIDS
Plasmids:
• usually small, closed circular DNA
molecules
• exist and replicate independently of
chromosome
• have relatively few genes present
…..PLASMIDS
•Plasmids are extra-chromosomal pieces of
DNA that are separate from the main DNA
structure.
•Some bacteria can carry more than one
plasmid.
•Plasmids often carry genes for toxins and
resistance to antibiotics.
•Plasmids can be transferred from one cell
to another through pili during conjugation.
Ribosomes
Ribosomes:
• Ribosomes are nonmembrane-enclosed
organelles involved in protein synthesis
• complex structures consisting of protein
and RNA (ribonucleic acid)
• sites of protein synthesis ( translation)
• smaller than eucaryotic ribosomes
– procaryotic ribosomes  70S
– eucaryotic ribosomes  80S
Clinical Significance
– The inhibition of protein synthesis is a lethal
event so ribosomes are a major target for
Cytoplasmic Inclusion Bodies:
Inclusion bodies are membrane-enclosed
organelles used to store important materials
Granules of organic or inorganic material
that are stockpiled by the cell for future
use (lipids,glycogen,protein, fat
globules) collectively called granules or
others called vesicles.
Granules contain glucose polymer for
energy, polyphospahte granules called
volutin, or iron containing vesiclesmagnetosomes
Bacterial Endospores
Bacterial Spores
• Endospores are formed through the process
of sporulation.
• They form when a bacterium is exposed to
great environmental stress.
• They are formed by some bacteria as
dormant structures.
• resistant to numerous environmental
conditions e.g heat, radiation,chemicals,
nutrient depletion,
desiccation, and waste buildup .
– Bacterial spores are NOT a reproductive
structure, like plant or fungal spores.
– Produced by very few genera of bacteria
– Major examples Bacillus & Clostridium
…endospores
Sporogenesis
..Spore Germination
Activation:
– prepares spores for germination
– often results from treatments like heating
Germination:
–
–
–
–
spore swelling
rupture or absorption of spore coat
loss of resistance to heat and other stresses
increased metabolic activity
Outgrowth:
– emergence of vegetative cell
Spore Germination
Bibliography
• Microbiology, A clinical Approach -Danielle
•
•
•
Moszyk-Strelkauskas-Garland Science 2010.
http://en.wikipedia.org/wiki/Scientific_method
http://www.bio.mtu.edu/campbell/prokaryo.htmhttp://
molecularbiology.suite101.com/article.cfm/cell_structure
http://water.me.vccs.edu/courses/ENV108/lesson5_2.ht
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