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28 Cards in this Set
- Front
- Back
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Define cell morphology and give the 4 different categories |
What a cell looks like under the microscope Rod - either gram negative (e.g. E.coli) or gram positive (Bacillus, anthracis). Cocci - gram positive (Neisseriameningitidis) or gram negative (staphylococcus aureus) Spirala - gram negative ((Treponema pallidum) Filaments/branching hyphae - gram positive (streptomyces) |
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Cell morphology of gram negative |
E-coli (rod) - found in guts of humans and animals, best studied microbe. There are some pathogenic stains Neisseria meningitidus (cocci) - colonies troat and infects blood and brain. Causes rapid infection. |
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Cell morphology of gram positive |
Lactobacillus acidophilus (rod) - yoghurt production, non pathogenic Staphylococcus aureus (cocci) - MRSA, colonises skin and nose, Travels in blood and infects other cells |
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Non staining cell morphology |
Treponema pallidum (gram negative) - causes syphillis Mycobacterium TB (gram positive) - acid fast stain. Difficult to treat as very slow growing |
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Grouping in cell morphology |
Diplococci –N.meningitidis Chains,repeated divisions in one plane – Streptococcus lactis,Bacillusmegaterium Grape-likeclusters’, division in several different planes e.g. Staphylococcus aureus Pleiomorphic, Coryneform – bacilli in palissades due to division, break up into coccias get older. • |
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How is grouping dependent on the divisions |
Divisions in single plane - results in chains or pairs of cells. Division is perpendicular to long axis of cell Division in all planes - results in cell clusters |
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How you describe bacteria |
Streak on a plate and look at the colonies Characteristic colour, shape, texture, edge, size Specific colony pattern (form, elevation and margin) Will react differently to different environments |
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Flagella |
Used for motility Polar monotrichous (at one end of cell) to peritrichous (all way round cell e.g. E-coli) that bundle together at back of cell Move towards nutrient sources (chemo attractants) and away from toxic agents (chemo repellents). |
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The movement of flagella |
Move counterclockwise - swim in one direction towards something they like Move clockwise - tumble, this occurs if they don't like something as move quicker Signals sent to DNA to give appropriate movement from receptors on cell Flagella motor - nanomachine that helps movement |
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Fimbriae |
Hair like fibres on cell surface allow bacteria to adhere to solid surface Recognise a specific molecule on cell surface by recognising tissue - this targets bacteria to a specific environment First step in invasion of host cell |
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F.pilus |
Much larger than Fimbriae Attach to recipient cell and transfer DNA directly from donor to recipient cell Bacteria divide by binary fission Whole genome or plasmid may be exchanged |
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Capsule |
Protection from desiccation, noxious substances and phagocytic cells Generally carbohydrate, gel like substance Macrophages cannot digest it, most cells cannot go through it |
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Mouse S and R strain to show principle of transformation |
Bacteria passed from S to R strain (DNA passed) S strain covered itself in protective capsule so mouse dies as bacteria were protected from host's immune system R strain did not have a capsule so mouse survives so bacteria killed by immune system. |
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The S-layer |
A regular crystalline protein surface layer which protects from bacteriophage (virus that infects bacteria) that forms part of cell envelope. Acts like a sieve, nutrients can get through but not harmful agents |
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Chromosome (nucleoid) |
Double stranded DNA formed of single circular chromosome with no membrane 1,400µm long within E.coli, tightly wound with histone proteins (supercoiled) Different strains have different combinations of genome due to horizontal transfer of DNA Sites of coupled active transcription/translation occur quickly, can double every 20-30mins |
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How do bacteria reproduce? BINARY FISSION |
1. Genome attached to membrane 2. Chromosome replicates (septum forms) 3. 2 daughter cells separate or form diplococci or cocci 4. Chromosome replication and cell division tightly replicated 5. Daughter cell identical to parent - one cell makes 2 daughter cells |
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Plasmids |
Double stranded DNA molecules that exist and replicate independently of chromosomes Composed of 100 thousand base pairs of nucleotides May integrate into genome if bigger Not required for growth and division (may confer critical phenotype e.g. antibiotic resistance as this can easily pass between species) Development of recombinant DNA |
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Horizontal transfer of genetic material |
Conjugation - F.pilus and plasmid Transformation - naked DNA (e.g. genome/plasmid) Transduction - bacteriophage (inject bacteria and pick up gene, smaller scale) E.coli evolved into new strain in 2011 causing outbreak |
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The cytosol |
70S ribosomes densely packed in cytosol mRNA rapidly degraded as protein synthesis is fast Storage bodies include glycogen, poly-B-hydroxybutyrate (fatty acid) and polyphosphate granules Gas vacuoles for buoyancy Magnetosome for orientation (according to poles) |
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Plasma membrane: structure and function |
A phospholipid bilayer with embedded proteins For transportation of nutrients, waste and macromolecules, energy creation and biosynthesis Barrier for small hydrophobic molecules - need a transport system |
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Differences between Bacteria, Archaea and Eukarya |
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Bacteria cell wall in gram positive bacteria |
One membrane (plasma membrane) with teichoic acids embedded in thick peptidoglycan |
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Bacteria cell wall in gram negative bacteria |
2 membranes (outer and plasma membrane) with thin peptidoglycan layer Lipopolysaccharides in outer membrane to protect bacteria Outer membrane freely permeable so low molecular weight solutes can diffuse through Evolved to survive in gut (bile salts) |
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The structure of peptidoglycan |
Disaccharide backbone made up of alternating Acetylmuramic acid and Acetylglucosamine Attached to Acetylglucosamine is 4 amino acids (peptide change) crosslinked by a pentaglycine interbridge to maintain structure and provide strength |
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The action of lysosyme |
Hydrolyses the backbone (between two sugars) so bacteria will burst as substance e,g. can get in (cell lysis). It breaks the B 1,4-glycosidic bonds Peptidoglycan gives protection against osmotic lysis (bursting) |
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Protoplast formation |
Protoplast - cell wall completely or partially removed Pencillin inhibits cross linking between proteins so inhibits peptidoglycan synthesis Water is therefore able to influx into the cell causing cell lysis |
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Endospores |
Highly resistant to heat, desiccation, radiation and chemicals so therefore do not stain Naturally present in soil and give survival to environment Different endospores allow for classification, central, subterminal, terminal or terminal and swollen sporangium. Spores remain present for long time e.g. C difficile in hospitals |
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Endospore formation |
Cell division - axial filament formation - septum formation - engulfment of forespore - cortex formation - coat synthesis - increase in heat resistance - formation of free spore, lysis of sporangium. |
