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Unit 15 – Assignment 2 – P5
Viruses
Bacteriophage:

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HIV viruses:

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The Baltimore classification system:

This system is based on genetic contents and replication strategies of viruses
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4
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6
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(-) sense ssRNA viruses
RNA reverse transcribing viruses

7
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All viruses must produce mRNA or (+)
sense RNA
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The Baltimore classification has a +
RNA as its central point
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The classical system - This is based on three principles:
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The nucleic acid genome
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g
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The genomic system:
More recently, a precise ordering of viruses within and between families is possible based on
DNA/RNA sequence
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The virus life cycle is characterised by:
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Penetration, with entry of nucleic acid into the cell
3
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4
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Synthesis of new Virion components
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Exit from cell
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Receptor-mediated endocytosis
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Bacteria
Shapes of cells:
Bacteria are put into five groups due to the shapes, which can either be single cells, in pairs, chains
or clusters
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Shapes of colonies:

Response to Gram staining:
The method of gram staining separates bacteria into two different types: gram-positive cells (these
retain the crystal violet-iodine complex, which therefore makes it appear purple), and gram-negative

cells (these are decolourised by the alcohol, but are stained pink with safranin)
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Fungi
The characteristics of the main subgroups of fungi:
Ascomycota – Both nuclear fusion and meiosis occur in the ascus
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In the ascus,
ascopores are formed by an enveloping membrane system
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The membranes are
obtained from the plasma membrane of the ascus (this is in the pezizomycotina) and the nuclear
membrane (this is in the saccaromycotina)
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However, under the right conditions, they are germinated to form a new haploid fungus
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It can either be singlecelled or it can be a long tubular filament (this is divided into cellular segments called hyphae
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They grow as mycelia or hyphae
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After a fusion
of specialised hyphae during the sexual cycle occurs in the zygosporangium, zygospores are formed
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A mature zygospore normally has a thick wall
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Most sygomycota have both
zygotic or haplontic life cycles, therefore the only diploid phase occurs in the zygospore
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Walled sporangiospores are made by the internal cleavage of the sporangial cytoplasm
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Basidiomycota – Basidiomycota are asexual or sexual, aquatic or terrestrial, and multicellular and
unicellular
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The most distinctive characteristic of the Basidiomycota, is the production of
cells on which sexual spores are produced; basidia
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Meiosis and
nuclear fusion both occur in the basidium
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Basidia can be directly formed from yeasts (and other single cells)
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On each basidium (on the tips of minute stalks), four
spores are made
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Hyphae or
haploid/uninucleate yeast cells are formed as a results of the germination or Basidiospores
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Deuteromycota is a form of this fungi; it is a polyphyletic group where several species are closely
related to organisms in other phyla than another
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Asexual reproduction of the deuteromycota mainly takes place by
the production of asexual conidiospores
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Between the different nucle is where genetic recombination occurs
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It contains peptidoglycan
(which is main which takes up 50-80% of the cell wall (this is what stains purple)
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The shape and stiffness of the cell wall
is a result of the cross-linked (by short chains of peptides), adjacent layers of peptidoglycan
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Fixed in the peptidoglycan layer, is lip teichoic acid which is made up of teichoic
acids
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This regulated the autolytic wall enzymes
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When it is rinsed with alcohol during the decolourisation process, the counter stain
safranin stays, whilst the crystal violet iodine complex is lost
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Gramnegative bacteria also have an outer membrane which is separated from the cell wall; it contains
lipids
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2
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4
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Spread the bread with water and left over a 3 period to grow mould
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Take the bread out of the bag and place on top of the bag when there is enough mould
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Place the tape over a slide and taped to it to keep it in place
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Repeat the process using another slide with a drop of methylene blue on it
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Penicillin is the
most likely possible fungi in this slide
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Streak plating
Method:
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They are stored in water baths at 60o C to keep them liquid
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Agar sets solid at about 40oC, but needs bringing up to 100oC to melt it again, so leave
bottles in water bath until required
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Swab benches with 70% ethanol
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4
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coli’ and the other ‘B
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Remove bottle of agar from waterbath
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Remember to flame the neck of the bottle
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Straight away, using the techniques of flaming the wire loop and bottle neck, take one
loopful of E
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coli’ Leave to set
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Repeat with B
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9
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B-sub – Rod shaped with entire margin
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E-coli – Rod shaped with entire margin and smooth surface colony edges
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Unit 15 – Assignment 2 – D4
Case study 1 - John
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By using the
method of streak plating, we would be shown the shape of the colony, which would help to
identify the bacteria
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We would know the type of bacteria it
is when we know the shape of the cell
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An alternative method to identify the strain of bacteria would be gene sequencing, as it
would identify the bacteria that is in the sample
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For this initial treatment, it is not necessary to identify the bacteria to either genus or
species level; the reason for this is because, in order to treat the illness, they only need to
identify what kills the bacteria
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Both gram staining and streak plating would be useful to find if Naomi had MRSA
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By using the method of gram staining, we can
identify if the bacteria is gram positive negative, as it would be stained purple
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2
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The reason for this
is because it is able to cause several hard-to-treat infections
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In this case, a strain of staphylococcus being resistant to the
beta lactam antibiotics
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3
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One
of these methods would be to carry out an MRSA test; by doing this, it would identify the
bacteria having a chemical structure that allows it to bind specifically with certain products
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If this was used, we would know the ratio of
the bases

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