1. obtain nitrogen - uptake of NH4 or NO2 - release of NH4 by decomposition 2. microbial oxidation of NH4 3. dentrification (NO3-NO-N2O) in anaerobic conditions (NO3 is terminal electron acceptor) 4. nitrogen fixation 5. nitrogen leaching from soil

Lectures 7-9 Flashcards by Sylvie Wilson

bacterial growth

binary fission

cell elongation
septum formation
completion of septum
formation of walls
cell separation

facilitated by proteins MinC, D and E

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MreB

protein essential for bacterial cell morphology

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stages of bacterial growth

lag
log/exponential
stationary
death

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effect of temperature on bacterial growth

low temp. - membrane gelling, transport processes too slow for growth
optimum - enzymatic reactions occur at max. rate
high temp. - protein denaturation, collapse of cytoplasmic membrane, thermal lysis

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psychrophile

bacteria with optimum temp between 0 and 10 degrees

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chemotroph

energy sourced from oxidation of organic and inorganic compounds

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lithotrophs and organotroph

use reduced inorganic compounds (litho) and organic compounds (organo) to source electrons

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organisms that source carbon from organic molecules from other orgnanisms

heterotrophs

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chemoorganoautotroph

chemo - energy from organic/inorganic compounds
organo - electrons sourced from organic compounds
auto - sources its own carbon

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reduction of pyruvate

by NADH (electron donor)

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homofermentative

if lactate is produced following glycolysis

if other mixed products are produced, the process is heterofermentative

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the nitrogen cycle

obtain nitrogen
- uptake of NH4 or NO2
- release of NH4 by decomposition
microbial oxidation of NH4
dentrification (NO3-NO-N2O) in anaerobic conditions (NO3 is terminal electron acceptor)
nitrogen fixation
nitrogen leaching from soil

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2 examples of nitrifying bacteria

nitrosomonas

nitrobacter

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DNA structure

H bonds between base pairs
double helix
anti-parallel strands - 3’ and 5’

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bacterial genomes

small compared to eukaryotes
genes densely packed
no introns
operons grouped together (genes with related functions)
coupled transcription and translation

plasmids may be present (replicate independently)
1 or 2 chromosomes

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episome

when plasmid becomes integrated into bacterial chromosomal DNA

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bacterial DNA replication

2 types:

bi-directional replication
- occurs during cell division

rolling circle replication
- occurs during conjugation

both occur during replication of some plasmids

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enzymes at the replication fork

helicase
DNA polymerase III
primase

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3 mechanisms of horizontal gene transfer

transformation - uptake of short DNA fragments

transduction - transfer of DNA via bacteriophages

conjugation - requires cell to cell contact

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natural transformation - gene transfer

3 stages:

competence - extracellular binding
uptake - conversion to single stranded DNA, stabilisation
integration - homologous recombination

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transduction

generalised - donor DNA from any part of donor can be transferred - lytic cycle

specialised - specific DNA region of donor transferred - lysogenic cycle

presence of F plasmid (an episome containing its own origin of replication)

ability to synthesis F pilus
mobilisation of DNA for transfer to another cell
alteration of cell surface receptors

cells with an integrated F plasmid are called Hfr

pathogenicity

the way in which a microorganism causes disease

factors influencing severity of a disease

host 
immunological status
physiological status
genetic make up
route of infection

in order to cause disease a pathogen has to...

colonise host tissues grow within host tissues avoid host defence mechanisms cause damage to the host

toxins as effectors

neurotoxins - cause paralysis enterotoxins - cause sickness and diarrhoea cytotoxins - cause cell death

AB toxins mechanism

B portion binds to cell and facilitates translocation of A which posesses catalytic properties

cytolytic toxins

damage cytoplasmic membrane

pathogen

microorganism that causes disease

LPS

endotoxin causes production of cytokines from immune cells upon binding to cell surface receptors

innate immunity

non-specific, general immediate response no immunological memory

innate immune cells

humoral: - complement - enzymes - cytokines cellular: - phagocytes - natural killer cells

features of adaptive immunity

specific to antigen lag time between exposure and response immunological memory after exposure

adaptive immune cells

humoral: - cytokines - antibodies cellular: - T cells - B cells

2 precursor molecules after bone marrow for immune cells

lymphoid precursor - thymus maturation to t cell - bone marrow maturation to B cell myeloid precursor - monocytes - go to dendritic cells and macrophages - granulocytes - go to mast cells and neutrophils

antibody structure

4 polypeptide chains - 2 heavy - 2 light antigen binding sites at the ends of both variable light chains

IgM structure

circulating as a pentamer (5 attached antibodies) or on surface of a B cell

which antibody is involved in primary response

IgM

which antibody is involved in secondary response

IgG

IgA

found in mucous, saliva, breast milk different shape to others

IgD

part of B cell receptor | activates basophils and mast cells

IgE

protects against parasitic worms | responsible for allergic reactions

IgG

secreted by plasma cells into the blood | crosses placenta into foetus

IgM

attached to surface of B cell OR secreted into blood | responsible for first stages of immunity

process of adaptive immunity - extracellular

antibodies recognise foreign pathogens and opsonise them | the phagocytes bind to the pathogens via their Fc receptors and eventually destroy them

process of adaptive immunity - intracellular

cytotoxic T cell binds to infected cell perforins from T cell make holes in membrane of infected cell infected cell lyses

describe the antibody production graph with respect to primary and secondary immune responses

initial antigen exposure: slow antibody production, steady increase until a low peak then steady decline but doesnt quite reach 0 second antigen exposure: rapid antibody production, peaks very high

types of vaccination

``` toxoid attenuated (live) conjugate vaccines DNA vaccines recombinant vector vaccines subunit ```

subunit vaccine

pathogen grown then chemicals used to split it apart only inject useful part e.g. epitope (binding site of antigen) chances of adverse reactions are lower used against Hep B

live attenuated vaccine

weakened version of live microbe elicit strong cellular/antibody responses and often cause lifelong immunity cannot be given to a weakened immune system microbes may mutate and become virulent easy to create need to stay refrigerated

how can we knock out genes

homologous recombination