1 Characteristics of microbes • Viruses Not cells; contain either RNA or DNA in envelope; can only multiply in living cells. Major groups of microorganisms • Bacteria Unicellular; 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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1 Characteristics of microbes Viruses Not cells; contain either RNA or DNA in envelope; can only multiply in living cells. Major groups of microorganisms.
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Characteristics of microbes
• VirusesNot cells; contain either RNA or DNA in envelope; can only multiply in living cells.
Archaebacteria• Non-peptidoglycan cell walls• Have unusual metabolic capabilities.• Live in extreme environments.• Methanogens, halophiles and thermoacidophiles.
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.
• 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.
• 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.