Transcript PPT - kimscience.com

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Bacterial Genetics
March 2015
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Terminology
 Genetics:
The study of what genes are, how they
carry information, how information is expressed, and
how genes are replicated
 Gene: A segment
of DNA that encodes a functional
product, usually a protein
 Chromosome:
Structure containing DNA that
physically carries hereditary information; the
chromosomes contain the genes
 Genome: All
the genetic information in a cell
– small circular DNA molecule that
replicates independently of the chromosome
 Plasmid
+ DNA
 Polymer
of nucleotides:
Adenine, thymine,
cytosine, and guanine
 Double
helix associated
with proteins
 "Backbone"
is
deoxyribose-phosphate
 Strands
are held together
by hydrogen bonds
between AT and CG
 Strands
are antiparallel
Figure 8.3b
+ DNA Synthesis
Figure 8.5
+ Replication of Bacterial DNA
Figure 8.6
+ Transcription
 DNA is
transcribed to make RNA (mRNA,
tRNA, and rRNA)
 Transcription
begins when RNA polymerase
binds to the promoter sequence
 Transcription
proceeds in the 5'  3'
direction
 Transcription
stops when it reaches the
terminator sequence
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The Process of Transcription
Figure 8.7
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Translation
 mRNA
is translated in
codons (three
nucleotides)
 Translation
of mRNA
begins at the start
codon: AUG
 Translation
ends at
nonsense codons:
UAA, UAG, UGA
Figure 8.2
+ Simultaneous Transcription &
Translation
Figure 8.10
+ Genetic Transformation –
Frederick Griffith (1920s)
Figure 8.24
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Recombinant DNA Technology
 Recombinant
DNA: DNA made from two
different sources.

In the 1960s, Paul Berg inserted animal DNA into bacterial
DNA, and the bacteria produced an animal protein
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Recombinant DNA Technology
 1941:
George Beadle and Edward Tatum
showed that genes encode a cell’s enzymes
 1944:
Oswald Avery, Colin MacLeod, and
Maclyn McCarty showed that DNA was the
hereditary material
 1961:
Francois Jacob and Jacques Monod
discovered the role of mRNA in protein
synthesis
+ The Flow of Genetic Information
Figure 8.2
+ Genetic
Recombination
 Vertical
gene transfer:
Occurs during
reproduction between
generations of cells.
 Horizontal
gene
transfer: The transfer of
genes between cells of
the same generation.
+ Genetic Recombination
Figure 8.25
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Transmission of Genetic Material in
Bacterial Cells
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Conjugation
+
Transformation
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Transduction
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3 main categories of genes
Structural
genes
• Code for
proteins
Regulatory
genes
• Control
gene
expression
RNA coding
genes
+ Operons: The Basic Concept
 Operator
-the regulatory “switch”, a segment
of DNA
 usually positioned within the promoter
– (DNA) includes the operator, the
promoter, and the genes that they control
 Operon
 In
coordinate control, a cluster of functionally
related genes can be controlled by a single onoff “switch”
+ Operons: Activation

Activator – (protein) when stimulated,
changes shape and binds to the promoter
to increase the affinity of RNA
polymerase to the promoter (increasing
the rate of transcription).
- The lac operon is stimulated by a small
organic molecule known as cAMP that is
produced in response to low cellular
glucose.
+ Operon: Lactose Metabolism
+ Lac Operon: Sensing Glucose vs.
Lactose
Bacterial will always prefer glucose over lactose
if it is available.
Thus, how does E. coli sense when glucose
levels are low?
How does it relay that information to the
genome?
+ Operons: Activation of Lac Operon
 Lactose
present
No glucose
 Lactose
and
Glucose present
Figure 8.15
+ Operons: Repression
– (protein) switches the operon off
 Prevents transcription by binding to the
operator and blocking RNA polymerase
 the product of a separate regulatory gene
 can be in an active or inactive form, depending
on the presence of other molecules
 Corepressor – cooperates with a repressor
protein to switch an operon off
 Repressor
+ Operons: Relieving Repression
 When
a repressor is bound to the operator,
RNA poly cannot bind the promoter and
transcription is turned “off”
 When
the repressor is not bound to the
operator, RNA poly can bind the promoter and
transcription is turned “on”.
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Biotechnology
 Recombinant
DNA technology, a new
technique for biotechnology, enables
bacteria and fungi to produce a variety of
proteins including vaccines and enzymes
 Missing or defective genes in human cells
can be replaced in gene therapy
 Genetically modified bacteria are used to
protect crops from insects and from
freezing
Figure 9.11
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pGLO Plasmid DNA
+
Lac Operon vs Ara Operon
+
Replacing Ara operon with GFP
gene
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Bacterial Conjugation
Figure 8.26
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Plasmids
Conjugative
plasmid: Carries genes
for sex pili and transfer of the plasmid
Dissimilation
plasmids: Encode
enzymes for catabolism of unusual
compounds
R
factors: Encode antibiotic resistance
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R Factor, a Type of Plasmid
Figure 8.29
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Conjugation in E. coli
Figure 8.27a
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Conjugation in E. coli
Figure 8.27b
+ Conjugation in E. coli
+ Transduction by a Bacteriophage
Figure 8.28