Microbial Genetics

1
Microbial Genetics
I. Structure and function of genes II. Gene
expression in bacteria III. Mutation and
variation IV. Horizontal gene transfer in
bacteria
2
Levels at which enzymes can be regulated
In prokaryotes, expression is generally regulated
at the level of _____________
3
In bacteria, genes are organized into operons

• Operon -- a cluster of genes whose expression is
  controlled by a single operator.
• Operator -- a specific region of the DNA at the
  initial end of a gene or operon, where a
  repressor protein binds and _______________ mRNA
  synthesis.
• Repressor protein -- a regulatory protein that
  binds to specific sites on DNA and blocks
  ______________________ .

4
One method of gene regulation enzyme
_________________
5
Enzyme induction, (cont.)
6
The lac Operon an example of enzyme
_____________
Repressor
?-galactosidase
http//esg-www.mit.edu8001/bio/pge/lac.html
7
When lactose is unavailable, the repressor is
_____________. It binds to the operator region,
blocking the binding of the ___________
______________________.
No mRNA and no protein
Repressor
http//esg-www.mit.edu8001/bio/pge/lac.html
8
The presence of lactose causes a conformational
change in the repressor, which renders it
________________ to bind the _____________________
_____
Blocked
lactose
http//esg-www.mit.edu8001/bio/pge/lac.html
9
Review lac operon without inducer
(________________)
http//www.biology.arizona.edu/molecular_bio/probl
em_sets/mol_genetics_of_prokaryotes/02t.html?
10
Review lac operon with inducer (lactose)
http//www.biology.arizona.edu/molecular_bio/probl
em_sets/mol_genetics_of_prokaryotes/02t.html?
11
Text, Fig. 9.21
12
Another method of gene regulation enzyme
________________
13
Enzyme repression (cont.)
14
An example of enzyme repression the
________________ operon
15
Review enzyme induction
16
Enzyme induction, (cont.)
17
Review enzyme repression
18
Enzyme repression (cont.)
19
Mutation

• Any permanent, _______________ change in the
  genetic information of a cell.
• Types
• Point mutations -- substitution, insertion, or
  deletion of _______________ or a few bases
• Large insertions or ________________

20
Point mutations -- effects of substitution
21
Point mutations (cont.) -- insertions and
deletions result in _________________ shifts
22
Insertions or deletions of large segments of DNA
can _________________ a gene (depending on where
the insertion lands)
Gene A
23
Transposable Elements _______________ genes
24
Palindromes Go hang a salami, I'm a lasagna hog
The mother of all palindromes
A man, a plan, a caret, a ban, a myriad, a sum, a
lac, a liar, a hoop, a pint, a catalpa, a gas, an
oil, a bird, a yell, a vat, a caw, a pax, a wag,a
tax, a nay, a ram, a cap, a yam, a gay, a tsar, a
wall, a car, a luger, a ward, a bin, a woman, a
vassal, a wolf, a tuna, a nit, a pall, a fret,
awatt, a bay, a daub, a tan, a cab, a datum, a
gall, a hat, a fag, a zap, a say, a jaw, a lay, a
wet, a gallop, a tug, a trot, a trap, a tram, a
torr, acaper, a top, a tonk, a toll, a ball, a
fair, a sax, a minim, a tenor, a bass, a passer,
a capital, a rut, an amen, a ted, a cabal, a
tang, a sun, anass, a maw, a sag, a jam, a dam, a
sub, a salt, an axon, a sail, an ad, a wadi, a
radian, a room, a rood, a rip, a tad, a pariah, a
revel, a reel, areed, a pool, a plug, a pin, a
peek, a parabola, a dog, a pat, a cud, a nu, a
fan, a pal, a rum, a nod, an eta, a lag, an eel,
a batik, a mug, amot, a nap, a maxim, a mood, a
leek, a grub, a gob, a gel, a drab, a citadel, a
total, a cedar, a tap, a gag, a rat, a manor, a
bar, a gal, a cola,a pap, a yaw, a tab, a raj, a
gab, a nag, a pagan, a bag, a jar, a bat, a way,
a papa, a local, a gar, a baron, a mat, a rag, a
gap, a tar, a decal,a tot, a led, a tic, a bard,
a leg, a bog, a burg, a keel, a doom, a mix, a
map, an atom, a gum, a kit, a baleen, a gala, a
ten, a don, a mural, apan, a faun, a ducat, a
pagoda, a lob, a rap, a keep, a nip, a gulp, a
loop, a deer, a leer, a lever, a hair, a pad, a
tapir, a door, a moor, an aid,a raid, a wad, an
alias, an ox, an atlas, a bus, a madam, a jag, a
saw, a mass, an anus, a gnat, a lab, a cadet, an
em, a natural, a tip, acaress, a pass, a baronet,
a minimax, a sari, a fall, a ballot, a knot, a
pot, a rep, a carrot, a mart, a part, a tort, a
gut, a poll, a gateway, alaw, a jay, a sap, a
zag, a fat, a hall, a gamut, a dab, a can, a
tabu, a day, a batt, a waterfall, a patina, a
nut, a flow, a lass, a van, a mow, anib, a draw,
a regular, a call, a war, a stay, a gam, a yap, a
cam, a ray, an ax, a tag, a wax, a paw, a cat, a
valley, a drib, a lion, a saga, aplat, a catnip,
a pooh, a rail, a calamus, a dairyman, a bater, a
canal--Panama.
Transposable element
G A C G T
C A T G C C G A C G T C T A C T G A A C G T C A G
T C C G T A C G G C T G C A G A T G A C T T G C A
G T C A G G
A C G T C
T G C A G
C T G C A
25
Disruption of a gene due to _______________ of a
transposable element
26
Mutation (cont.)

• Causes
• Spontaneous -- due to ________________ mistakes
  or background effects
• Frequency varies from 1 in ______ to 1 in _______
  depending on organism
• Bacteria have such short generation times and
  grow to such high populations that spontaneous
  mutants can be isolated quickly and easily
• Induced -- exposure to mutagens such as
  ______________ or _________________

27
Spontaneous (antibiotic) mutants
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Mutagenesis by electromagnetic radiation
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Chemical mutagenesis
30
Horizontal gene transfer in bacteria

• Conjugation -- direct (________________) transfer
  between bacteria
• Transformation -- uptake of naked,
  __________________ DNA (often plasmids)
• Transduction -- transfer of DNA from one cell to
  another by a _____________.

31
Conjugation
A copy of the plasmid is made in the recipient
cell, resulting in a plasmid in each cell
32
Text, Fig. 9.27
33
____________________
Donor cell dies and lyses, releasing DNA
The free DNA is taken up by a recipient cell, and
incorporated into its genome
34
Griffiths classic experiment in transformation
Fig. 9.28
35
__________________
36
Text, Fig. 9.29
37
How is the DNA incorporated?

• homologous recombination -- genetic exchange
  between (nearly) _________________ DNA sequences
  from 2 different sources
• ________________ into chromosome
• not incorporated into genome at all, but still
  functional -- e.g. plasmids