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Characteristics of microbes
Major groups of microorganisms
• Viruses
Not cells; contain either RNA or DNA in envelope; can only multiply
in living cells.
• Bacteria
Unicellular; procaryotic; rigid cell wall; absorb nutrients.
Archaebacteria; eubacteria
Archaebacteria
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Non-peptidoglycan cell walls
Have unusual metabolic capabilities.
Live in extreme environments.
Methanogens, halophiles and thermoacidophiles.
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Characteristics of microbes
Major groups of microorganisms 2
• Fungi
Either uni- or multicellular; eucaryotic; rigid cell walls; absorb
nutrients.
• Protozoa
Single celled; eucaryotic; lack rigid cell wall; ingest food.
• Algae
Either uni- or multicellular; eucaryotic; rigid cell walls; chlorophyll;
absorb nutrients.
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Structure/function of eubacteria
Size, shape and arrangement
Diameter
Length
Ave.
0.5 - 1 m
up to 500 m
1.1 - 1.5 m wide
2.0 - 6.0 m long (E. coli )
Spherical
Rods
Spiral
coccus (sing.) cocci (pl.) meaning “berries”.
bacillus (sing.) bacillus (pl.) meaning “little staffs”.
spirullum (sing.) spirilla (pl.)
Pleomorphy variety of shapes in a species
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Structure/function of eubacteria
Size, shape and arrangement 2
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Structure/function of eubacteria
Size, shape and arrangement 3
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Structure/function of eubacteria
Ultrastructure
Cell wall
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Structure/function of eubacteria
Ultrastructure 2
• Cell wall
Rigid, strong structure; gives and maintains shape.
10 - 40% of dry weight of the cell.
Usually essential for cell division.
A barrier to some substances.
Not homogeneous structures; depending on species, layered with
different substances which have different thicknesses.
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Structure/function of eubacteria
Ultrastructure 3
• Peptidoglycan (a.k.a. murein)
Shape determining part of the wall.
Insoluble, porous polymer of great strength and rigidity.
Comprises N-acetylglucosamine, N-acetylmuramic acid and
tetrapeptides.
Peptidoglycan chains are cross-linked at the tetrapeptide units.
Autolysin opens the network for addition of new polymer.
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Structure/function of eubacteria
Ultrastructure 3
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Structure/function of eubacteria
Ultrastructure 4
There are 2 types of cells wall in eubacteria
• Gram stain differently
• Differences in the layering and presence of outer membrane (in G -)
explains the difference in Gram reaction and pathogencity.
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Structure/function of eubacteria
Ultrastructure 5
The G(+) cell wall
• Peptidoglycan content  50%cf. G(-)  10%
 walls of G(+) bacteria appear thicker.
• Contains techoic acid (may aid in the transport of cations).
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Structure/function of eubacteria
Ultrastructure 5
The G(-) cell wall
• More complex; has outer membrane covering a thin layer of
peptidoglycan.
• Outer membrane: Contains lipolysaccharides (lipid portion causes
toxic effects in infected animals).
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Structure/function of eubacteria
Ultrastructure 5
Cytoplasmic membrane
• Composition:
Phospholipids 20 - 30%
Proteins
50 - 70%
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Structure/function of eubacteria
Ultrastructure 6
Cytoplasmic membrane 2
• A site of specific enzyme activity, transport of molecules in and out
of the cell, and invaginations participate in cell metabolism and
replication.
• Some processes essential to the cell are located here.
A barrier to most water-soluble molecules, and is more selective than the
cell wall.
Permeases transport small molecules into the cell.
Also contains various enzymes for energy production and synthesis of cell
wall.
• Photosynthetic bacteria or those with metabolisms based on gas
exchange have elaborate intracellular extensions of the cytoplasmic
membrane.
This infolding increases the area for light pigments or gas exchange.
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Structure/function of eubacteria
Ultrastructure
Cytoplasmic area
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Structure/function of eubacteria
Ultrastructure 6
Cytoplasmic area
• 80% water with nucleic acids, proteins, carbohydrates, lipids,
inorganic ions, many low-molecular weight compounds and
particles with various functions.
• Ribosomes. Free in cytoplasm, not membrane-bound.
• Cell inclusions (insoluble chemical substances accumulated)
e.g. metachromatic granules (a.k.a volutin; a reserve of inorganic phosphate).
Lipids e.g. poly--hydroxybutyrate; reserve carbon and energy
source.
Sulfur: H2S-oxidizing bacteria.
Polysaccharides e.g. glycogen and starch; reserve energy
sources.
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Structure/function of eubacteria
Ultrastructure
Nuclear area
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Structure/function of eubacteria
Ultrastructure 6
Nuclear area
• No nuclear membrane. Nuclear material found near the center of
the cell and is attached to the mesosome-cytoplasmic membrane.
• Total nuclear material = nucleoid; consist of a single circular
chromosome.
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Structure/function of eubacteria
Ultrastructure
Flagella
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Structure/function of eubacteria
Ultrastructure 6
Flagella(e)
• Thin, helical, hair-like
filaments; extends from
the cytoplasm through the
cell wall. Observable in
stained specimens.
E. Coli
© Dennis Kunkel
• Propels the cell.
Up to 100 m min-1.
3000 cell lengths min-1
cf. the cheetah’s top speed of 1500 body lengths min-1.
• Polar flagellation: monotrichous; lophotrichous; amphitrichous.
• Peritrichous flagellation
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Structure/function of eubacteria
Ultrastructure 7
Fimbria(e)
• Hair-like appendages not
related to motility. Shorter
and straighter than
flagella
• Either polar or even distribution.
Number from few to thousands.
E. Coli
© Dennis Kunkel
• Enables adhesion. A factor in pathogenicity.
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Structure/function of eubacteria
Ultrastructure 8
Pilus(i)
• Usually longer than
fimbriae.
• Number only one or two.
• Join cells in preparation for
transfer of DNA.
Thus also known as sex pili.
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Structure/function of eubacteria
Ultrastructure 9
Glycocalyx
• Layer of viscous material (usually polysaccharides) outside the cell
wall.
Observation: Indian ink stained specimens.
• When well defined: capsule.
disorganized: slime layer.
• Function: Adhesion; protection against desiccation; prevent
attachment by bacteriophages or attack by white blood cells.
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Characteristics of viruses
Living organisms?
• Inert outside a living host
• Obligatory intracellular parasites
• Either: complex aggregation of non-living chemicals or simple living
microorganism.
Distinctive features
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Single type of nucleic acid; DNA or RNA.
Protein coat surrounds the nucleic acid (NA).
Synthetic processes of a host living cell used to multiply.
Specialized structures for transfer viral NA to other cells.
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Characteristics of viruses
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Viral structure
Virion
A complete, fully developed viral particle composed of nucleic acid surrounded
by a protective coat which also serves as a vehicle of transmission from one
host cell to another.
Nucleic acid
• Contrasts with pro- and eucaryotic cells where DNA is the primary
genetic material.
• Total NA: From a few thousand to as many as 250,000 nucleotide
pairs.
E. coli has 4 million nucleotide pairs.
• NA is single or double stranded; linear or circular.
• May be in separate segments e.g. influenza virus.
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Viral structure
Capsid
• Protein coat surrounding the nucleic acid.
• Capsomere: Protein subunits of the capsid.
Arrangement is characteristic of each particular virus.
• Nucleocapsid: Capsid and nucleic acid as a unit.
• Capsids give virus types their typical shapes.
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Viral structure
Envelope
• Outer membranous layer; lipids, carbohydrates and proteins.
• Present in many animal and some plant viruses.
• In animal viruses: Host cell nuclear or plasma membranes contribute
envelope lipids and carbohydrates.
Envelope proteins are made by the virus.
• Some have spikes (a.k.a. peplomers); are carbohydrate-protein
complexes.
Thought to be involved in attachment to hosts.
Useful in identification since they differ amongst viruses.
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Viral structure
Four general morphological types of virion structure
• Helical viruses
Capsomeres arranged in a helical around the nucleic acid.
• Polyhedral viruses
Capsids are icosahedral in arrangement (20 equilateral triangular
faces and 12 corners).
• Enveloped viruses
Roughly spherical but pleomorphic as the envelope is not rigid. Capsid
can be helical or polyhedral. Non-enveloped viruses are “naked”
viruses.
• Complex viruses
Have capsid symmetry but neither purely helical or polyhedral.
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Viral structure
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The eucaryotic cell
Protozoa, algae and fungi are eucaryotic.
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The eucaryotic cell
Ultrastructure
• Flagella and cilia
Few and long - Flagella
Short and few - cilia
Motility; movement of substances (cilia)
Both: 9 ring pairs and 2 central microtubules.
• Glycocalyx
Surrounds animal cells.
Strengthens cells; also means of attachment to other cell.
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The eucaryotic cell
Ultrastructure 2
• Cell wall
Algae and some fungi: cellulose.
Fungi: chitin.
• Cytoplasmic membrane
Like procaryotes: Phospholipid bilayer containing proteins.
Contains CHO attached to proteins and sterols not found in procaryotes.
Capable of endocytosis.
• Cytoplasm
Resemble that of procaryotes.
Has cytoskeleton and exhibits cytoplasmic streaming.
Unlike procaryotes, many important enzymes are sequestered in
organelles.
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The eucaryotic cell
Ultrastructure 3
• Cell wall
Algae and some fungi: cellulose.
Fungi: chitin.
• Cytoplasmic membrane
Like procaryotes: Phospholipid bilayer containing proteins.
Contains CHO attached to proteins and sterols not found in procaryotes.
Capable of endocytosis.
• Cytoplasm
Resemble that of procaryotes.
Has cytoskeleton and exhibits cytoplasmic streaming.
Unlike procaryotes, many important enzymes are sequestered in
organelles.
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The eucaryotic cell
Ultrastructure 4
Organelles
• Nucleus
Contains DNA in the
form of chromosomes.
Most characteristic of
eucaryotes.
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The eucaryotic cell
Ultrastructure 5
Organelles
• Endoplasmic reticulum
Not present in procaryotes.
Provides surface for chemical
reactions.
Serves as transport network.
Stores synthesized molecules.
• Ribosomes
Attached to outer surface of ER but
also found free.
Larger than procaryotic ribosomes.
Site of protein synthesis.
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The eucaryotic cell
Ultrastructure 6
Organelles
• Golgi complex
Consists of cisternae.
Secretion; CHO and glycoprotein
synthesis.
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The eucaryotic cell
Ultrastructure 7
Organelles
• Mitochondrion(a)
Folding of inner membrane provides large surface area for
chemical reactions e.g. ATP production (primary site) and
cellular respiration.
Can multiply on their own by fission.
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The eucaryotic cell
Ultrastructure 8
Organelles
• Lysosomes
Formed from golgi complexes.
Contain digestive enzymes to breakdown molecules and
invasive bacteria.
• Centrioles
Role in cell division and as basal bodies in the formation of
flagella and cilia.
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The eucaryotic cell
Ultrastructure 6
Organelles
• Chloroplast
Algae/green plants only.
Contains DNA, ribosomes, chlorophyll and photosynthetic pigments.
Can multiply on their own by fission.
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