This is a full summary of all content required for the A1.1 (from DNA Organisation to the end of Trp Operon). These are the same summaries found under Jansen Microbiology 314.
Please note that I do use my own abbreviations, but the notes are still applicable and understandable.
DNA PACKAGING AND REPLICATION
1. Genomes of prok. = single “chromo”
2. Genome = circular, double-stranded DNA molec
3. Sizes of bacterial genomes vary
4. E.coli ~1.3mm long (extended form), chromo more compact
5. Phages & plasmids much smaller
GENOME PACKAGING
Prokaryote Eukaryote
Single “chromo” Multiple chromo
In vivo compact gnm DNA density ~
~ 100mg/ml
10mg/ml
Nucleoid = 80% DNA, 20% prot Nucleus = 50% DNA, 50% prot
Packaging ratio vs extended DNA 1000-2000x - 7000x in mitotic div
Prot assoc w DNA genome identified eg. HU & H (basic prot, like histones in euk.)
↳ DNA coils around HU prot, forms nucleosome-like struct
Integrative Host Factor (IHF) charactersitics similar to HU, but specifically involved in lambda
integration. HLP1 binds to DNA - conformation affected by its absence
DNA binding proteins in E.coli:
Eukaryotic
Protein Composition number/cell Locus
equivalent
αand βunits
HU 50 000 dimers histone H2B hupA, B
9 kDaeach
2 identical
H 30 000 dimers histone H2A Not known
28 kDaunits
αunit (10,5 kDa)
IHF 15 000 dimers HMG himA, D
β unit (9,5 kDa)
H1
15 kDaunit 20 000 copies Not known Not known
H-NS
NUCELOID
= round/oval mass w coiled domains, extend from center. -ve
supercoil of 1 -ve superhelical winding for every 20 windings
(200bp/winding) & packed in loop-shaped domains (100-200 in
a gnm). Bottom ends held tog by prot. Break in doub stranded
DNA, -ve supercoil of 1 domain will unwind, adjacent domains
will be retained. - vely coiled domains each ~40kb DNA
= Repetitive DNA seq = REPs (Repeated Extragenic
Palindromes_ ~ 70bp long; 100-200x in gnm; absent w/in genes
DNA binding prot assoc w REPs bring loop-like domains tog &
DNA gyrase binds near REPs - provides necessary -ve supercoiling
Shannon Goodchild
072 827 0597
, Microbiology 314
GENE ORGANISATION
Certain genes in grps (eg 7rrn loci - contains r/tRNA genes, found near OriC)
Studies where hisD-gene placed on diff parts E.coli gnm = transcr. 3x more actively near
OriC (probs why 7rrn loci are there)
Inversions (Hin syst) - HIn recombon - rotation of 980bp section, allows cntrl expression
alternating flagella genes
EUKARYOTIC DNA ORGANISATION
More specialised - 5 diff levels
Sim to prok = DNA packed by means of prot & -ve supercoiling maintained
Higher level packing in euk = req higher % prot found in chromo
ONE GENE: ONE POLYPEPTIDE HYPOTHESIS
Beadle & Ephrussi examined mutants of fruit fly w abnormal eye clr to solve biosynth p/w for
red eye clr pigment
Should be possible to gen mutants which known biochem rxn not occur
Beadle & Tatum gen mutants of bread fungus Neurospora crassa - expose fungus to UV
irradiation
↳ mutants tested for inabil grow on min media that original, wild-type able to grow on
↳ mut req certain nutritional components ∴ rep blocks in metabolic p/w ∴ rep absence of
certain enz
Lead to 1 gene:1 enz hypothesis - enz = prot
1957, Ingram proved mut in gene for haemoglobin responsible for sickle-cell anemia which
confirmed this hypothesis
Later, known enz & other struct prot consist +1 polypep ∴ adjust to 1 gene : 1 polypep:
“One gene codes for the AA of one polypep chain - the basic struct unit of prot.”
Shannon Goodchild
072 827 0597
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