Lecture 1 - Microbial structure and genetics Flashcards
Why are bacteria such great models for understanding microbial physiology?
- know about their component parts and how they function to produce new cells
- know how cells respond to their envirnoment to maximise their growth and survival in the environment
What is the model of microbial growth in their natural environment?
‘feast and famine’
-mostly starving, and short period of quick growth
What is the optimal doubling time for E.coli, and why is this not refletive of their natural environment or helpful to experiments?
20mins
- on a rich undefined medium growth medium when grown aerobically at 37*C
- want defined growth media for experiments
- E.coli is a gut facultative anaerobe, a minor player in the gut and so naturally would have lots of competetion
- lives of sugars in the diet, which naturally would varey hugely
What is a prototroph and give an example of an organism
Prototroph
- an organism or cell capable of synthesizing all its metabolites from inorganic material, requiring no organic nutrients.
e. g. E.coli
Why is it useful that E.coli can also grow on a chemically defined minimal medium?
- know exactly what the chemicals are being used for cell growth
- whereas many other bacteria are more fastidious and need growth supplements e.g. blood agar (not v scientific)
What are the componants necessary for a minimal media in which to grow e.coli?
- buffers e.g. K2HPO4, to maintain pH 7 and to provde phosphate
- a nitrogen source e.g. (NH4)2SO4 for the synthesis of amino acids and nucleotides
- Magnesium (as an enzyme cofactor)
- carbon source
- CaCl2
What is the structure of E.coli?
- gram negative (envelope structure) (requires sugar for peptidoglycan in envelope)
- flagella
- cytosol (1000-2000 different proteins, 60 tRNAs, glycogen)
- coupled transcription/translation
How many key precursors are synthesised in the cytoplasm of E.coli, and what is necessary for their synthesis?
13 precursors
- all biosynthetic pathways originate from these
- can be synthesised from glucose (E.coli has a preferential use of glucose)
What experimental technique would be used to determine how E.coli synthesises an amino acid e.g. histadine?
- As normal E.coli is a prototroph we can grow it on a minimal medium where it must synthesise histadine to grow
- nutritional mutants can be isolated - E.coli that cannot grow unless histadine is present in the medium (have a mutation in one of the genes necessary for the biosynthesis of histadine)
- a number of mutants could be isolated and through genetics these could be demonstarted to be becuase of different genes on the chromosome
- mutants could then be complemented using an E.coli gene library to identify the genes responsible
- this would reveal the pathway for histadine biosynthesis
What are the features of the E.coli genome?
- single circular chromosome of 4.6Mb (varies between species)
- contains around 4500 genes (88% DNA is coding)
- single ORI
- bidirectional replication resulting in two replichores of equal length
- majority of genes are protein encoding, although also have, tRNA, sRNA, rRNA, bacteriophage componants and pseudogenes.
How many genes are thought to be involved in E.coli metabolism?
around 2000
What are the different locations that proteins could reside in the cell?
cytoplasm inner membrane periplasmic outermembrane extracellular
Different compartments in the bacterial cell
What is proteonomics?
the study of all the proteins that are present in a particular cell at a particular time
-on 2D gel, separates proteins via charge AND size
