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Define genetics, genome, chromosome, gene, genetic code,
genotype, phenotype, and genomics.
Describe the process of DNA replication.
Describe protein synthesis, including transcription, RNA
processing, and translation.
Classify mutations by type, and describe how mutations are
prevented and repaired.
Define mutagen.
Describe two ways mutations can be repaired.
Outline methods of direct and indirect selection of mutants.
Identify the purpose and outline the procedure for the Ames
test.
Compare the mechanisms of genetic recombination in
bacteria.
Differentiate between horizontal and vertical gene transfer.
Describe the functions of plasmids and transposons.
Student Learning Outcomes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
TerminologyCom
ple
menta
ry b
ut a
ntip
ara
llel
DNA
Genetics
Genome
Gene
Chromosome
Base pairs
Genetic code
Genomics
Genotype
Phenotype
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The Bacterial DNA
Mostly single circular chromosome
Attached to plasma membrane
DNA is supercoiled
Number of genes in E. coli
Extra-chromosomal bacterial DNA: _________(1-5% of chromosome size)
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E. coli
Figure 8.1a
Fig 8.1
Figure 8.1b
Chromosome Map of E. coli
Chromosome length:
1mm
Cell length ?
Flow of Genetic Information
Fig 8.2 – Foundation Figure
DNA Replication
DNA polymeraseinitiated by RNA primer
bidirectional
origin of replication
leading strand:continuous DNA synthesis
lagging strand: discontinuous DNA synthesis Okazaki fragments
semiconservative
2
Replication forkReplication in 5' 3' direction
Fig 5.8
Fig 8.6
Replication 1; 2; 3
of circular
bacterial
Chromosome
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Protein Synthesis
Genetic code: universal and degenerate (or redundant)
Transcription produces 3 types of RNA (?) Enzyme necessary ? Promoters and terminators
Translation produces the protein Sense codons vs. nonsense codons anticodons
Fig 8.9
Fig 8.7
Fig 8.8
Compare to Fig 8.8
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Transcription RNA polymerase binds to promotor sequence
proceeds in 5' 3'direction
stops whenit reaches terminator sequence
Fig 8.7
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More Details on Translation
Nucleotide sequence of mRNA is translated into amino acid sequence of protein using “three letter words” = codons
Translation of mRNA begins at the start codon: AUG
Translation ends at a stop codon: UAA, UAG, UGA
Requires various accessory molecules and 3 major components: ?
In Prokaryotes: Simultaneous transcription and translation Polyribosomes
The Translation Process in Protein
Synthesis
Compare to Fig 8.9
Simultaneous Transcription and Translation
in Prokaryotes
Compare to Fig 8.10
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MutationsChange in genetic material.
1. Point mutations = base pair substitution (silent, missense, nonsense)
2. Frameshift mutations = Insertion or deletion of one or more nucleotide pairs
Review Fig 8.17
Various Point Mutations
Silent
Missense
Nonsense
Fig 8.17
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Mutations cont.
May be neutral (silent), beneficial, or harmful.
Spontaneous mutation rate 10-6 1 mutation per million replicated genes
Mutagens increase mutation rate 10 – 1000x
Chemical mutagens Nucleoside (base) analogs have altered base-
pairing properties. They can be randomly incorporated into growing cells (cancer drugs)
only used by viral enzymes (e.g. AZT)
Frameshift mutagens such as intercalating agents (e.g.:, aflatoxin, ethidium bromide)
Fig 8.19a
Distortion due to
intercalating agent
will lead to one or
more base-pairs
inserted or deleted
during replication.
Potent carcinogens!
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Radiation as a Mutagen
1. Ionizing radiation (x-rays and -rays)lead to deletion mutations (ds breaks)
2. UV rays lead to thymine dimers (intrastrand bonding)
Photolyases = light repair enzymes (use energy from visible light to fix UV light damage)
Nucleotide excision repair for repair of all mutations
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Fig 8.20
Repair
ANIMATION Mutations: Repair
Photolyases separate thymine dimers
Nucleotide excision repair
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Mutagen Identification: Ames Test
Wild type vs. mutant
Auxotroph vs. prototroph
Many mutagens are carcinogens
Combine animal liver cell extracts with Salmonella
auxotroph
Expose mixture to test substance
Examine for signs of mutation in Salmonella, i.e.
Look for cells (colonies) that have reverted from his– to
his+
Fig. 8.22
Ames Reverse Gene Mutation Test
Positive or
negative
Ames
test?
Explain
what
happened
Professor Richard A. Muller of
UC Berkeley on the Ames Test
and Natural Foods
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Genetic Transfer and Recombination
Vertical gene transfer: Occurs during
reproduction between generations of cells.
Horizontal (lateral) gene transfer: Transfer
of genes between cells of the same
generation. Leads to genetic recombination
Three mechanisms of horizontal gene
transfer:
Transformation
Conjugation
Transduction
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Vertical gene transfer: Occurs
during reproduction between
generations of cells.
Horizontal gene transfer: The
transfer of genes between cells of
the same generation. Leads to
genetic recombination.
Three mechanisms of horizontal
gene transfer:1. Transformation
2. Conjugation
3. Transduction
ANIMATION Horizontal Gene Transfer: Overview
Genetic Recombination
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Genetic Recombination
Exchange of
genes between
two DNA
molecules
Crossing over
occurs when two
chromosomes
break and rejoin
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1) Transformation
“Naked” DNA transfer
Recipient cells have to be “competent”
Occurs naturally among very few genera (G+
and G–)
Simple laboratory treatment will make E. coli
competent workhorse for genetic
engineering
Griffith’s historical experiment in 1928
ANIMATION Transformation
Griffith’s Experiment to Demonstrate Genetic Transformation
Fig 8.24
Fig 8.25
Transformation and Recombination
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2) Conjugation
Plasmid and chromosomal DNA transfer via direct cell to cell contact
High efficiency
F+ = donor cell. Contains F plasmid (factor) and produces conjugation (F) pilus (aka “sex pilus”)
Recipient cell (F– ) becomes F+
In some cells F factor integrates into chromosome Hfr cell
R plasmids (R factors) are also transferred via conjugation
Fig 8.26
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3) Transduction
DNA Transfer from donor to
recipient cell with help of
bacteriophage (= transducing
phage)
2 types of phage-bacteria interaction:
1. Generalized transduction happens via
lytic cycle caused by virulent phages
2. Specialized transduction will be covered in
Ch 13
Fig 8.27
ANIMATION Generalized
Transduction
ANIMATION Specialized
Transduction
Transduction by a Bacteriophage
Fig 8.28
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