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Characteristics of microbes

• VirusesNot cells; contain either RNA or DNA in envelope; can only multiply in living cells.

Major groups of microorganisms

• BacteriaUnicellular; procaryotic; rigid cell wall; absorb nutrients. Archaebacteria; eubacteria

Archaebacteria• Non-peptidoglycan cell walls• Have unusual metabolic capabilities.• Live in extreme environments.• Methanogens, halophiles and thermoacidophiles.

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Characteristics of microbes

• FungiEither uni- or multicellular; eucaryotic; rigid cell walls; absorb nutrients.

Major groups of microorganisms 2

• ProtozoaSingle celled; eucaryotic; lack rigid cell wall; ingest food.

• AlgaeEither uni- or multicellular; eucaryotic; rigid cell walls; chlorophyll; absorb nutrients.

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Structure/function of eubacteria

Size, shape and arrangement

Diameter LengthAve.

0.5 - 1 mup 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

• Cell wall

Ultrastructure 2

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

• Peptidoglycan (a.k.a. murein)

Ultrastructure 3

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.

Shape determining part of the wall.Insoluble, porous polymer of great strength and rigidity.

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Structure/function of eubacteria Ultrastructure 3

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Structure/function of eubacteria

There are 2 types of cells wall in eubacteria

Ultrastructure 4

• 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

The G(+) cell wall

Ultrastructure 5

• 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

The G(-) cell wall

Ultrastructure 5

• 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

Cytoplasmic membraneUltrastructure 5

• Composition: Phospholipids 20 - 30% Proteins 50 - 70%

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Structure/function of eubacteria

Cytoplasmic membrane 2

Ultrastructure 6

• 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

Cytoplasmic area

Ultrastructure 6

• 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

Nuclear area

Ultrastructure 6

• 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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Flagella(e)

Ultrastructure 6

• Thin, helical, hair-like filaments; extends from the cytoplasm through the cell wall. Observable in stained specimens.

• 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.

• Peritrichous flagellation

• Polar flagellation: monotrichous; lophotrichous; amphitrichous.

Structure/function of eubacteria

E. Coli © Dennis Kunkel

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Fimbria(e)

Ultrastructure 7

• Hair-like appendages not related to motility. Shorter and straighter than flagella

• Either polar or even distribution.Number from few to thousands.

• Enables adhesion. A factor in pathogenicity.

Structure/function of eubacteria

E. Coli © Dennis Kunkel

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Pilus(i)

Ultrastructure 8

• Usually longer than fimbriae.

• Number only one or two.

• Join cells in preparation for transfer of DNA.Thus also known as sex pili.

Structure/function of eubacteria

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Structure/function of eubacteria

Glycocalyx

Ultrastructure 9

• 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• 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 virusesCapsomeres arranged in a helical around the nucleic acid.

• Polyhedral virusesCapsids 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 ciliaFew and long - FlagellaShort and few - ciliaMotility; movement of substances (cilia)Both: 9 ring pairs and 2 central microtubules.

• GlycocalyxSurrounds animal cells.Strengthens cells; also means of attachment to other cell.

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The eucaryotic cell

Ultrastructure 2

• Cell wallAlgae and some fungi: cellulose.Fungi: chitin.

• Cytoplasmic membraneLike procaryotes: Phospholipid bilayer containing proteins.Contains CHO attached to proteins and sterols not found in procaryotes.Capable of endocytosis.

• CytoplasmResemble 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 wallAlgae and some fungi: cellulose.Fungi: chitin.

• Cytoplasmic membraneLike procaryotes: Phospholipid bilayer containing proteins.Contains CHO attached to proteins and sterols not found in procaryotes.Capable of endocytosis.

• CytoplasmResemble 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

• NucleusContains DNA in the form of chromosomes. Most characteristic of eucaryotes.

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The eucaryotic cell

Ultrastructure 5

Organelles

• Endoplasmic reticulumNot present in procaryotes.Provides surface for chemical reactions.Serves as transport network.Stores synthesized molecules.

• RibosomesAttached 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 complexConsists 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

• LysosomesFormed from golgi complexes.Contain digestive enzymes to breakdown molecules and invasive bacteria.

• CentriolesRole in cell division and as basal bodies in the formation of flagella and cilia.

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The eucaryotic cell

Ultrastructure 6

Organelles

• ChloroplastAlgae/green plants only.Contains DNA, ribosomes, chlorophyll and photosynthetic pigments.Can multiply on their own by fission.