Download Chapter 8: Microbial Genetics

Chapter 8:
Microbial
Genetics
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Bacteria
Single circular chromosome
Genome: genetic
information in a cell
Chromosome: contains
the genes-segments
of DNA
DNA: nucleotide base
pairs - genetic code
for proteins
Central Dogma:
DNA - RNA - Proteins
Genomics: sequencing
and molecular
characterization of
genomes
Looped and folded and attached at one or several points to the plasma
membrane
THAT SPELLS DNA
Jonathan Coulton
http://www.jonathancoulton.com/store/downloads/
We start the story when Mom met Dad
And they danced all night and he took her home
It might have been all the wine they had
But they rolled the dice and won your genome
Then you grew and you grew and one day you were you
And you looked like your father and mother
IF you’re looking for someone convenient to blame
You can take your pick it’s one or the other
DNA, you’re in my heart
DNA, in fact you’re in every part of my body
Each cell has a nucleus, each nucleus has chromosomes
And DNA, baby, that spells DNA
Guanine met Cytosine, fell in love
And then Thymine got busy with Adenine
They sent the messenger-RNA
To the ribosome to make more protein
And while it’s killing you dead it will mess with your head
And it’s the light in the dark that will guide you
It’s the pages and pages of what you are like
In the giant book that’s hidden inside you
DNA, you’re in my heart
DNA, in fact you’re in every part of my body
Each cell has a nucleus, each nucleus has chromosomes
And DNA, baby, that spells DNA
If it says TGGTCGAAC
Then you might get the cancer
If it says GTCACGACAGG
Then you shouldn’t eat shrimp or nuts
If it says TATACACATATCCTCGT
Then you’ll probably wish that you didn’t know
The time will come when you’re almost gone
And you try to guess but you’ll never know
You do your best and you soldier on
Every day you’re here till it’s time to go
All the good things and bad that you do or don’t have
You can find out for sure if you got’em
But there’s a spiraling staircase that you’re falling down
And you’re nothing but dead at the bottom
DNA, you’re in my heart
DNA, in fact you’re in every part of my body
Each cell has a nucleus, each nucleus has
chromosomes
And DNA, baby, that spells DNA
Replication
Transcription
DNA
Translation
RNA PROTEINS
Replication
Transcription
DNA
Translation
RNA PROTEINS
• Semiconservative replication: each new DNA
molecule contains one original and one new
strand
• Requires TONS of energy - supplied by the
nucleotides (nucleoside triphosphates)
*Two phosphates are removed to add the nucleotide to a
growing stand
*Hydrolysis (exergonic)
• Accurate: mistakes made in 1 in every 1010
bases
***Proofreading-DNA pol
Replication
Transcription
DNA
Translation
RNA PROTEINS
Bacteria:
• Some replicate bidirectionally around the chromosome
• Two replication forks move in opposite direction away
from the origin of replication
• Eventually meet when replication is complete
Ex: E.coli
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TRANSCRIPTION
file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_A
nimations/transcription_process.swf
TRANSLATION
file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation_process.swf
file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation.swf
GENE REGULATION
• Turning on and off genes
• Save energy and resources
• Repression: Turns OFF
– Response to overabundance of an end product
– Repressors block RNA pol
GENE REGULATION
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• Induction: Turns ON
•
•
•
•
– Inducer: acts to induce transcription
– EX: lac operon
E. coli (bacteria that live in intestines of mammals)
Discovered how genes control the metabolism of the sugar
lactose
Lactose: disaccharide made of glucose and galactose
Milk sugar
– http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related
When there is/is not lactose
LACTOSE PRESENT: It induces E. coli
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metabolize
lactose
LACTOSE ABSENT: three enzymes will
not be made. Lactose will not be
broken down.
DNA of E.coli
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Regulator gene: codes for repressor gene
Promoter: DNA segment that is recognized by the enzyme RNA
pol
Operator: DNA segment that serves as a “switch” controlling the
access of RNA pol to the promoter
Structural genes: code for 3 enzymes that break down lactose
Operon “turned off”
• Repressor protein attaches to the operator
physically blocking RNA pol from attaching
RNA pol
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Operon “turned on”
• Lactose present (acts as inducer
starts gene expression)
• Binds to the repressor protein
• Repressor changes shapes and
detaches from operator
• RNA pol is not blocked anymore
• All three enzymes can be produced
Operator “turned on”
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lactose
Why is this
good?
• E. coli is able to turn off and on genes
when lactose is present/absent
• Bacteria saves resources and
produce only those proteins that are
needed
Let’s watch it again
• http://www.youtube.com/watch?v=oBwtxdI1zvk&featu
re=related
MuTaTiOnS
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• GOOD
– New enhanced activity
that benefits the cell
• BAD
– Inactive or less active,
lethal?
• SILENT(neutral)
– No change in activity
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Types of Mutations
Base Substitution (point)
• Single base in DNA is replaced
Missense mutation: substitution results in an
amino acid substitution
Nonsense mutation: creates a stop codon in the
middle of mRNA....preventing synthesis of
protein
Types of Mutations
Frameshift
• One or a few nucleotide pairs are deleted or inserted
in the DNA
• Change the reading frame of codons
*Mutations can occur spontaneously or by mutagens
MUTAGENS
• Chemical:
– Nitrous acid (HNO2): causes A to bond with C
instead of T
MUTAGENS
• Radiation: x-rays, UV rays, gamma rays
– Cause electrons to pop out of their usual shells
– Ions can combine with bases in DNA, resulting in errors in
DNA
– Breakage of covalent bonds in sugar-phosphate backbonebreaks in chromosomes
• Exposure to UV causes
T’s to cross link forming
a thymine dimer
• Unless repaired, these
may cause serious
damage or death to the
cells because it cannot
properly transcibe or
replicate.
• Some organisms have
enzymes that can repair
these dimers
Genetic Transfer and Recombination
1. Conjugation: transfer of a plasmid
2. Transduction: transfer of DNA via a virus
3. Transformation: genes transferred from one
bacterium to another as “naked” DNA
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Conjugation
Movement of a plasmid
b/w two cells
Plasmid: small, self-replicating,
gene-containing circular
piece of DNA
1. Requires direct cell
to cell contact
2. Opposite mating
types (donor cell has
a plasmid, recipient
cells do not)
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Transduction
• Bacterial DNA is
transferred from a
donor cell to recipient
inside a virus that
infects bacteria
• Bacteriophage
(phage)
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•First done 70 yrs ago: Griffith
•http://www.dnatube.com/video/997/Transformation
HOW DOES THIS HAPPEN?
Can happen naturally after cell death and cell lysis
• Cell wall becomes permeable to large DNA molecules
• Use surface proteins and type 4 pili to extend and take it in
• Works best when donor and recipient cells are closely related
Artificial transformation:
– Competence: when recipient cell is in a physiological state
to take up donor DNA
– Changing the ionic strength of the medium and heating the
cells in the presence of positive ions (Calcium)
– Makes cell membrane permeable
We are going to do this!!!
pBLU Transformation
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• Use an ampicillin-sensitive
strain of E. coli, incapable
of producing bgalactosidase for lactose
breakdown
• Induce it to take up pBLU
plasmid DNA
• Plasmid contains genes
for Ampicillin resistance
and the entire bglactosidase gene
• http://www.biologie.uni-hamburg.de/bonline/library/onlinebio/14_1.jpg