Microbiology Ch 07 lecture_presentation

© 2015 Pearson Education, Inc.
Chapter 7

The Structure and Replication of Genomes
• Genetics
• Study of inheritance and inheritable traits as expressed
in an organism's genetic material
• Genome
• The entire genetic complement of an organism
• Includes its genes and nucleotide sequences

Figure 7.1 The structure of nucleic acids.
Hydrogen bond
Sugar
Adenine (A)
nucleoside
Thymine (T)
nucleoside
A–T base pair (DNA) A–U base pair (RNA)
Adenine (A)
nucleoside
Uracil (U)
nucleoside
Guanine (G)
nucleoside
Cytosine (G)
nucleoside
Double-stranded DNA
3′ end
5′ end
3′ end
Adenine Thymine
5 end′
Thymine nucleoside
Guanine Cytosine
G–C base pair (DNA and RNA)
5′ end 5′ end3′ end
Thymine nucleotide
T A
CG
A T
G
3′ end

• The Structure of Prokaryotic Genomes
• Prokaryotic chromosomes
• Main portion of DNA, along with associated proteins and
RNA
• Prokaryotic cells are haploid (single chromosome copy)
• Typical chromosome is circular molecule of DNA in
nucleoid

Figure 7.2 Bacterial genome.
Nucleoid
Bacterium
Chromosome
Plasmid

• The Structure of Prokaryotic Genomes
• Plasmids
• Small molecules of DNA that replicate independently
• Not essential for normal metabolism, growth, or
reproduction
• Can confer survival advantages
• Many types of plasmids
• Fertility factors
• Resistance factors
• Bacteriocin factors
• Virulence plasmids

• The Structure of Eukaryotic Genomes
• Nuclear chromosomes
• Typically have more than one chromosome per cell
• Chromosomes are linear and sequestered within nucleus
• Eukaryotic cells are often diploid (two chromosome
copies)

Figure 7.3 Eukaryotic nuclear chromosomal packaging.
10 nm
Histones
Linker
DNA
DNA
10 nm
Nucleosomes Chromatin fiber Euchromatin and
heterochromatin
Highly condensed,
duplicated
chromosome of
dividing nucleus
Active
(loosely packed)
Inactive
(tightly
packed)
Nucleosome
30 nm 700 nm
1400 nm

• The Structure of Eukaryotic Genomes
• Extranuclear DNA of eukaryotes
• DNA molecules of mitochondria and chloroplasts
• Resemble chromosomes of prokaryotes
• Code only for about 5% of RNA and proteins
• Some fungi, algae, and protozoa carry plasmids

• DNA Replication
• Key to replication is complementary structure of the two
strands
• Replication is semiconservative
• New DNA composed of one original and one daughter
strand
• Anabolic polymerization process that requires
monomers and energy
• Triphosphate deoxyribonucleotides serve both functions

DNA Replication: Overview

DNA Replication

Figure 7.4 Semiconservative model of DNA replication.
Original
DNA
First
replication
Second
replication
Original strand
New strands

Guanosine triphosphate deoxyribonucleotide (dGTP)
Guanine nucleotide (dGMP)
High-energy
bond
DeoxyriboseGuanine base
Guanosine (nucleoside)
Existing DNA strand
Triphosphate
nucleotide
Diphosphate released,
energy used for synthesis
Longer DNA strand
OH
Figure 7.5 The dual role of triphosphate deoxyribonucleotides as building blocks and energy sources in DNA synthesis.

• DNA Replication
• Initial processes in bacterial DNA replication
• Replication begins at the origin
• DNA polymerase replicates DNA only 5′ to 3′
• Because strands are antiparallel, new strands are
synthesized differently
• Leading strand synthesized continuously
• Lagging strand synthesized discontinuously

Figure 7.6a DNA replication.
Chromosomal proteins
(histones in eukaryotes and
archaea) removed
DNA helicase
Replication fork
DNA polymerase III
Initial processes
Stabilizing proteins
3′
5′

DNA Replication: Replication Proteins

Primase
RNA primer
Leading strand
Triphosphate
nucleotide
Replication fork
Synthesis of leading strand
Replication fork
Triphosphate
nucleotide
Okazaki
fragment Lagging
strand
DNA ligase
DNA polymerase IDNA polymerase IIIPrimase
RNA
primer
Synthesis of lagging strand
9
8
7
6
10
2
3 1
P P+
3′
5′
3′
5′
Figure 7.6b-c DNA replication.

DNA Replication: Forming the Replication Fork

DNA Replication: Synthesis

• DNA Replication
• Other characteristics of bacterial DNA replication
• Bidirectional
• Gyrases and topoisomerases remove supercoils in DNA
• DNA is methylated
• Control of genetic expression
• Initiation of DNA replication
• Protection against viral infection
• Repair of DNA

Figure 7.7 The bidirectionality of DNA replication in prokaryotes.
Origin Parental
strand
Daughter
strand
Replication forks
Replication
proceeds in
both directions Termination
of replication

• DNA Replication
• Replication of eukaryotic DNA
• Similar to bacterial replication
• Some differences
• Uses four DNA polymerases
• Thousands of replication origins
• Shorter Okazaki fragments
• Plant and animal cells methylate only cytosine bases

• Tell Me Why
• DNA replication requires a large amount of energy, yet
none of a cell's ATP energy supply is used. Why isn't it?

Gene Function
• The Relationship Between Genotype and
Phenotype
• Genotype
• Set of genes in the genome
• Phenotype
• Physical features and functional traits of the organism
• Genotype determines phenotype
• Not all genes are active at all times

Gene Function
• The Transfer of Genetic Information
• Transcription
• Information in DNA is copied as RNA
• Translation
• Polypeptides are synthesized from RNA
• Central dogma of genetics
• DNA is transcribed to RNA
• RNA is translated to form polypeptides

Figure 7.8 The central dogma of genetics.

Transcription: Overview

Translation: Overview

Gene Function
• The Events in Transcription
• Five types of RNA transcribed from DNA
• RNA primers
• mRNA
• rRNA
• tRNA
• Regulatory RNA
• Occur in nucleoid of prokaryotes
• Three steps
• Initiation
• Elongation
• Termination

Figure 7.9a The events in the transcription of RNA in prokaryotes.
RNA polymerase attaches
nonspecifically to DNA and
travels down its length until
it recognizes a promoter
sequence. Sigma factor
enhances promoter
recognition in bacteria.
Upon recognition of the
promoter, RNA polymerase
unzips the DNA molecule
beginning at the promoter.
Unzipping of DNA, movement of RNA polymerase
Attachment of RNA polymerase
Sigma factorPromoter
RNA polymerase
"Bubble"
Terminator
Template
DNA strand
DNA
Initiation of transcription
5′
3′
5′
5′ 3′
3′
5′
3′
1a
1b

Figure 7.9b The events in the transcription of RNA in prokaryotes.
Triphosphate ribonucleotides
align with their DNA
complements and RNA
polymerase links them
together, synthesizing RNA.
No primer is needed. The
triphosphate ribonucleotides
also provide the energy
required for RNA synthesis.
Elongation of the RNA transcript
Growing RNA molecule
(transcript)
"Bubble"
Template
DNA
strand
2
5′
3′
3′
5′
5′
5′
3′
3′
3′
5′C
G

Figure 7.10 Concurrent RNA transcription.
3′
3′ 3′ 3′ 3′ 3′ 3′
3′
5′
5′
5′
5′5′
5′
5′
5′
Promoter
RNA polymerases
Sigma factor
RNA
Template DNA
strand

Figure 7.9c The events in the transcription of RNA in prokaryotes.
3′
5′
5′
3′
3′
3′
5′
Self-termination: transcription of GC-rich terminator
region produces a hairpin loop, which creates tension,
loosening the grip of the polymerase
on the DNA.
Rho-dependant termination: Rho pushes between polymerase
and DNA. This causes release of polymerase, RNA transcript,
and Rho.
GC-rich
hairpin
loop
Termination of transcription: release of RNA polymerase
Template
strand
Rho protein moves
along RNA
Rho termination
protein
RNA polymerase
RNA transcript
released
Terminator
C
3b3a
Terminator
Terminator

Transcription: The Process

Gene Function
• The Events in Transcription
• Transcriptional differences in eukaryotes
• RNA transcription occurs in the nucleus
• Transcription also occurs in mitochondria and chloroplasts
• Three types of nuclear RNA polymerases
• Numerous transcription factors
• mRNA is processed before translation
• Capping
• Polyadenylation
• Splicing

3′
3′
3′ 5′
5′
5′
5′
Introns (noncoding regions)
Template
DNA strand
Exon 1
cap Intron 1 Intron 2 Intron 3
Exon 2 Exon 3
Pre-mRNA
Poly-A tail
Exon 1
Spliceosomes
Exons (polypeptide coding regions)
Processing
mRNA splicing
mRNA (codes for
one polypeptide)
Nuclear envelope
Nucleoplasm
Cytosol
mRNA
Nuclear pore
Exon 2
Exon 3
AAAAAAAAAAAAAA
AAAAAAAAAAAAAA
AAAAAAAAAAAAAA
Intron 1
Transcription
Figure 7.11 Processing eukaryotic mRNA.

Gene Function
• Translation
• Process in which ribosomes use genetic information of
nucleotide sequences to synthesize polypeptides

Figure 7.12 The genetic code.

Translation: Genetic Code

Gene Function
• Translation
• Participants in translation
• Messenger RNA
• Transfer RNA
• Ribosomes and ribosomal RNA

Figure 7.13 A single prokaryotic mRNA can code for several polypeptides.
5′
5′3′
3′
Promoter Gene 1 Gene 2 Gene 3 Terminator
Template
DNA strand
Start
codon
AUG
Start
codon
AUG
Start
codon
AUGUAA UAG UAA
Ribosome
binding
site (RBS)
Stop
codon
RBS Stop
codon
RBS Stop
codon
Untranslated
mRNA
mRNA
Polypeptide 1 Polypeptide 2 Polypeptide 3
Translation
Transcription

Figure 7.14 Transfer RNA.
Acceptor
stem
Hydrogen
bonds
Hairpin
loops
tRNA icon
Anticodon
Anticodon
5′
5′
3′
3′
OH

Figure 7.15 Ribosomal structures.

Figure 7.16 Assembled ribosome and its tRNA-binding sites.
Large
subunit
mRNA
Small
subunit
Prokaryotic ribosome
(angled view) attached
to mRNA
Large
subunit
Nucleotide
bases
Prokaryotic ribosome
(schematic view) showing
tRNA-binding sites
Small
subunit
tRNA-
binding
sites
E
site
P
site
A
site
mRNA
5′ 3′

Gene Function
• Translation
• Events in translation
• Three stages of translation
• Initiation
• Elongation
• Termination
• All stages require additional protein factors
• Initiation and elongation require energy (GTP)

Figure 7.17 The initiation of translation in prokaryotes.
fMet
Initiator
tRNA
Anticodon
mRNA Start codon
Small
ribosomal
subunit
GTP GDP P
fMet
tRNA
fMet
Initiation complex
5′ 3′
fMet
Large
ribosomal
subunit
U
U U U AU GGA C
A C
AP
U U U AU GGA C
AP
U U U AU GGA C
U A C
AP
1 2 3
E
+

Figure 7.18 The elongation stage of translation.

Figure 7.19 In prokaryotes a polyribosome—one mRNA and many ribosomes and polypeptides.
mRNA Ribosomes Polypeptides mRNA Ribosomes Polypeptides
Direction of
transcription

Gene Function
• Translation
• Events in translation
• Termination
• Release factors recognize stop codons
• Modify ribosome to activate ribozymes
• Ribosome dissociates into subunits
• Polypeptides released at termination may function
alone or together

Translation: The Process

Gene Function
• Translation
• Translation differences in eukaryotes
• Initiation occurs when ribosomal subunit binds to 5′
guanine cap
• First amino acid is methionine rather than f-methionine
• Ribosomes can synthesize polypeptides into the cavity of
the rough endoplasmic reticulum

Protein Synthesis

Gene Function
• Regulation of Genetic Expression
• Most genes are expressed at all times
• Other genes are transcribed and translated when cells
need them
• Allows cell to conserve energy
• Quorum sensing regulates production of some proteins
• Detection of secreted quorum-sensing molecules can
signal bacteria to synthesize a certain protein

Gene Function
• Regulation of polypeptide synthesis
• Typically halts transcription
• Can stop translation directly

Gene Function
• Nature of prokaryotic operons
• An operon consists of a promoter and a series of genes
• Controlled by a regulatory element called an operator
• Typically polycistronic (code for several polypeptides)

Figure 7.20 An operon.
Operon
Promoter Operator Structural genes
Template DNA strand
Regulatory gene
5′
4321
3′

Gene Function
• Nature of prokaryotic operons
• Inducible operons must be activated by inducers
• Lactose operon
• Repressible operons are transcribed continually until
deactivated by repressors
• Tryptophan operon

Operons: Overview

Template DNA
strand
Template DNA
strand
RNA polymerase
lac operon
Operator
(blocked)PromoterPromoter and
regulatory gene
Continual transcription
Repressor mRNA
Repressor
lac operon repressed
Lactose catabolism genes
Transcription
proceedsRepressor
cannot bind
Repressor
Inactivated
repressor
Inducer (allolactose
from lactose)
lac operon induced
mRNA for
lactose catabolism
2 31
3′
3′ 5′
5′
5′
RNA
polymerase
cannot
bind
1
2
3
4
2 31
Continual translation
Repressor mRNA
Figure 7.21 The lac operon, an inducible operon.

Figure 7.22 CAP-cAMP enhances lac transcription.
CAP
binding
site
lac genes
RNA
polymerase
Transcription proceeds
Promoter Operator
cAMP
bound to
CAP

Operons: Induction

Figure 7.23 The trp operon, a repressible operon.
Regulatory gene
mRNA
Inactive repressor
trp operon active
Promoter
trp operon with five genes
Transcription
Enzymes of tryptophan biosynthetic pathway
Template DNA strand
Tryptophan
Operator
blocked
Inactive
repressor
trp operon repressed
Trp
3′
Movement of RNA
polymerase ceases
Trp
Tryptophan
(corepressor) Activated
repressor
mRNA coding
multiple polypeptides
5′ 3′
Operator
5′
1 2 3 4 5
5′
3′
1 2 3 4 5
5′
Trp
Trp
Trp
Trp
3′

Operons: Repression

Gene Function
• RNA molecules can control translation
• Regulatory RNAs can regulate translation of polypeptides
• microRNAs
• Produced by eukaryotic cells
• Bind regulatory proteins to form miRNA-induced
silencing complex (miRISC)
• Bind complementary mRNA and inhibit its
translation
• Regulates several cellular processes

Gene Function
• RNA molecules can control translation
• Regulatory RNAs can regulate translation of polypeptides
• Short interference RNA (siRNA)
• RNA molecule complementary to a portion of
mRNA, tRNA, or DNA
• Binds RISC proteins to form siRISC
• siRISC binds and cuts the target nucleic acid
• Riboswitch
• RNA molecule that changes shape to help
regulate translation

Gene Function
• Tell Me Why
• In bacteria, polypeptide translation can begin even
before mRNA transcription is complete. Why can't this
happen in eukaryotes?

Mutations of Genes
• Mutation
• Change in the nucleotide base sequence of a genome
• Rare event
• Almost always deleterious
• Rarely leads to a protein that improves ability of
organism to survive

Mutations of Genes
• Types of Mutations
• Point mutations
• One base pair is affected
• Substitutions and frameshift mutations
• Frameshift mutations
• Nucleotide triplets after the mutation are displaced
• Creates new sequence of codons

Mutations: Types

Figure 7.24 The effects of the various types of point mutations.

Mutations of Genes
• Mutagens
• Radiation
• Ionizing radiation
• Nonionizing radiation
• Chemical mutagens
• Nucleotide analogs
• Disrupt DNA and RNA replication
• Nucleotide-altering chemicals
• Alter the structure of nucleotides
• Result in base-pair substitutions and missense
mutations
• Frameshift mutagens
• Result in nonsense mutations

Mutagens

Figure 7.25 A pyrimidine (in this case, thymine) dimer.
Ultraviolet light
Thymine dimer
G
C
C T G T A
GG
G A C A A C C A T
T T=

Figure 7.26 The structure and effects of a nucleotide analog.

Figure 7.27 The action of a frameshift mutagen.

Mutations of Genes
• Frequency of Mutation
• Mutations are rare events
• Otherwise, organisms could not effectively reproduce
• About 1 of every 10 million genes contains an error
• Mutagens increase the mutation rate by a factor of 10 to
1000 times
• Many mutations stop transcription or code for
nonfunctional proteins

Mutations: Repair

Figure 7.28a-b DNA repair mechanisms.
Visible light
Thymine dimer
Light-activated
repair enzyme
Cut
Repair
enzyme
Light repair
Dark repair
DNA polymerase I
and ligase repair
the gap
G A C A
C T G A A T
T
C T G A A T
G A C AT T
T=
C T G A A T
G A C AT T
G
C
C T G A A T
G
A C A
T T
G
C
C T G A A T
G A C A
T T
G
C
=
=

Figure 7.28c-d DNA repair mechanisms.
Base excision repair enzymes
remove incorrect nucleotide
DNA polymerase I
and ligase repair gap
Mutated DNA
(incorrect nucleotide pair)
Mismatch repair enzyme
removes incorrect segment
DNA polymerase III correctly
repairs the gap
Mismatch repair
Base-excision repair
C C G A A T
G G C AT T
A
T C G T
G C AC C G A A T
G G C AT T
A
C G T
G C AC C G A A T
G G C AT T
A
G C G T
G C A
G G A T
C AT T
C
G C G T
G C A G G A T C
G C G T
G C A G G A T
C AC T
C
G C G T
G C A

Mutations of Genes
• Identifying Mutants, Mutagens, and Carcinogens
• Mutants
• Descendants of a cell that does not repair a mutation
• Wild types
• Cells normally found in nature
• Methods to recognize mutants
• Positive selection
• Negative (indirect) selection
• Ames test

Figure 7.29 Positive selection of mutants.
Medium with penicillin
(only penicillin-resistant
cell grows into colony)
Medium without
penicillin (both
types of cells form
colonies)
Penicillin-
sensitive cells
Penicillin-
resistant cell
Penicillin-
resistant
mutants
indistinguishable
from nonmutants
Medium with penicillin Medium without
penicillin
Mutagen
induces
mutations

Figure 7.30 The use of negative (indirect) selection to isolate a tryptophan auxotroph.
Bacteria
Stamp replica plates
with velvet.
Complete medium
containing
tryptophan
Medium lacking
tryptophan
Incubation
Identify auxotroph
as colony growing on
complete medium but
not on lacking medium.
Tryptophan auxotroph
cannot grow.
All colonies grow.
Inoculate auxotroph
colony into complete
medium.
X X
XX
4
5
6
Bacterial
suspension
Bacterial colonies
grow. A few may be
tryptophan
auxotrophs. Most are
wild type.
Incubation
Mutagen
Inoculate bacteria onto
complete medium
containing tryptophan.
Stamp sterile velvet onto
plate, picking up cells
from each colony.
Sterile velvet
surface
3
2
1
X
X
X

Figure 7.31 The Ames test.
Colony of revertant
(his+
) Salmonella
No growth
Incubation
Medium
lacking
histidine
Liver
extract
Experimental
tube
Suspected
mutagen
Liver
extract
Control
tube
Culture of his–
Salmonella

Mutations of Genes
• Tell Me Why
• Changes in RNA resulting from poor transcription of
RNA to DNA are not as deleterious to an organism as
changes to its DNA resulting from mutations. Why is this
the case?

Genetic Recombination and Transfer
• Exchange of nucleotide sequences often occurs
between homologous sequences
• Recombinants
• Cells with DNA molecules that contain new nucleotide
sequences

Figure 7.32 Genetic recombination.
Homologous
sequences
Enzyme nicks one strand of
DNA at homologous sequence.
Recombination enzyme
inserts the cut strand
into second molecule,
which is nicked in the
process.
Ligase anneals nicked ends
in new combinations.
Molecules resolve
into recombinants.
Recombinant A
Recombinant B
3′
DNA A
DNA B
5′
3′
5′
A
B

• Horizontal Gene Transfer Among Prokaryotes
• Vertical gene transfer
• Passing of genes to the next generation
• Horizontal gene transfer
• Donor cell contributes part of genome to recipient cell
• Three types
• Transformation
• Transduction
• Bacterial conjugation

Horizontal Gene Transfer: Overview

• Transformation
• Recipient cell takes up DNA from the environment
• Provided evidence that DNA is genetic material
• Cells that take up DNA are competent
• Results from alterations in cell wall and cytoplasmic
membrane that allow DNA to enter cell

Figure 7.33 Transformation of Streptococcus pneumoniae.
Observations of Streptococcus pneumoniae
Live cells
Injection
Capsule
Heat-treated
dead cells of
strain S Injection
Strain R live cells
(no capsule)
Injection
Griffith's experiment:
Living
strain R
Mouse dies
Mouse lives
Mouse lives
Heat-treated
dead cells
of strain S
Injection
Mouse dies
Culture of
Streptococcus
from dead
mouse
Living cells
with capsule
(strain S)
In vitro transformation
Heat-treated
dead cells of
strain S
DNA broken
into pieces
DNA fragment
from strain S
Living strain R
Some cells take
up DNA from the
environment and
incorporate it into
their chromosomes
Transformed cells
acquire ability to
synthesize capsules
+

Transformation

• Transduction
• Transfer of DNA from one cell to another via replicating
virus
• Virus must be able to infect both donor and recipient cells
• Virus that infects bacteria called a bacteriophage (phage)

Figure 7.34 Transduction.
Phage injects its DNA.
Phage enzymes
degrade host DNA.
Phage
DNA
Cell synthesizes new
phages that incorporate
phage DNA and, mistakenly,
some host DNA.
Transducing phage
injects donor DNA.
Donor DNA is incorporated
into recipient's chromosome
by recombination.
Inserted
DNA
Transduced cell
Recipient host cell
Transducing phage
Phage with donor DNA
(transducing phage)
Bacterial chromosome
Bacteriophage
Host bacterial cell
(donor cell)
1
2
3
4
5

• Transduction
• Generalized transduction
• Transducing phage carries random DNA segment
from donor to recipient
• Specialized transduction
• Only certain donor DNA sequences are transferred

Transduction: Generalized Transduction

Transduction: Specialized Transduction

• Conjugation
• Genetic transfer requires physical contact between the
donor and recipient cell
• Donor cell remains alive
• Mediated by conjugation (sex) pili

Conjugation: Overview

Conjugation: F Factor

F plasmid Origin of
transfer
Pilus Chromosome
F
Donor cell attaches to a recipient cell with
its pilus.
Pilus may draw cells together.
One strand of F plasmid DNA transfers
to the recipient.
The recipient synthesizes a complementary
strand to become an F+ cell with a pilus; the
donor synthesizes a complementary strand,
restoring its complete plasmid.
Pilus
1
+ cell
2
F+ cell
3
4
F
_
cellF+cell
Figure 7.35 Bacterial conjugation.

Figure 7.36 Conjugation involving an Hfr cell.
Donor chromosome
Pilus
F+ cell
Hfr cell
Pilus
F+ cell (Hfr)
F plasmid Donor DNA Part of F plasmid
F recipient
Incomplete F plasmid;
cell remains F−
F plasmid integrates
into chromosome by
recombination.
Cells join via a pilus.
Portion of F plasmid partially
moves into recipient cell
trailing a strand of donor's
DNA.
Conjugation ends with pieces
of F plasmid and donor DNA
in recipient cell; cells synthesize
complementary DNA strands.
Donor DNA and recipient
DNA recombine, making a
recombinant F cell.
Recombinant cell (still F− )
–
1
2
3
4
5
–

Conjugation: Hfr Conjugation

Conjugation: Chromosome Mapping

• Transposons and Transposition
• Transposons
• Segments of DNA that move from one location to another
in the same or different molecule
• Result is a kind of frameshift insertion (transpositions)
• Transposons all contain palindromic sequences at each
end

Figure 7.37 Transposition.
DNATransposon
Jumping transposons. Transposons
move from one place to another
on a DNA molecule.
Replicating transposons. Transposons
may replicate while moving, resulting in
more transposons in the cell.
Transposons can move onto plasmids.
Transposons moving onto plasmids can
be transferred to another cell.
Plasmid with
transposon

Transposons: Overview

• Transposons and Transposition
• Simplest transposons
• Insertion sequences
• Have no more than two inverted repeats and a gene for
transposase
• Complex transposons
• Contain one or more genes not connected with
transposition

Figure 7.38 Transposons.
Transposon: Insertion sequence IS1
Inverted repeat (IR) Transposase gene Inverted repeat (IR)
Target site
DNA
molecule
IS1
Target IS1
Transposase
Target site Copy
of IS1
Copy of
target site
Original
IS1
Complex transposon
IS1
Kanamycin-
resistance
gene IS1
IR
A C T GT A C T TA
T G A A T G A C T A
T
A A
A AA
A
TT
TTTT
AC G G
G C C
IRIRIR

Transposons: Insertion Sequences

Transposons: Complex Transposons

• Tell Me Why
• Why is the genetic ancestry of microbes much more
difficult to ascertain than the ancestry of animals?

Important topics
• Structure of chromosome
– DNA
– Histon
– Chromatid
– Nucleosome
• Comparison between bacterial and eukaryotic chromosome
• Bacterial plasmid
– Structure
– Function
• Replication process
• Transcription process
• Translation process
• Different forms of mutation
– Frameshift
– Silent
– Missense
– Nonsense
• Transformation vs. conjugation and transduction

Microbiology Ch 07 lecture_presentation

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