BIO 208 Unit 3 - Microbial Genetics and Viruses
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Unit 3 lecture notes start on page 10.
Review - Important Concepts for Lectures over Microbial Genetics
Pages 1- 9 are a quick review of basic genetics that you were exposed to on BIO 110. Please
refresh your memory. Some of this we will go over again quickly, and some we will not, but it will
help you to appreciate what the Bacteria and Archaea do differently from the Eukarya, if you
remember what the Eukarya do 
The sequence of the nucleotide bases in a nucleic acid has meaning. In the language of nucleotides,
the bases are like letters. The 4 bases can be arranged in 256 (44) different combinations (words).
By convention we represent the sequence of nucleotides by the identity of the bases (since that is
where the meaning is), and just as we read left to right, we “read” a nucleic acid polymer from 5’
to 3’.
Just as STOP and POTS have different meaning so to would TAGC versus CGAT.
So in the polymer below, the sequence of bases read from 5’ to 3’ is: 5’-T-A-G-C-3’
H3 C
T
H
A
H
G
H
C
H
BIO 208 Unit 3 - Microbial Genetics and Viruses
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If 2 strands of nucleic acid come close to each other, the bases of the nucleotides will form hydrogen
bonds with their complement bases (called “base pairing”). Remember that A forms H bonds with T
(A and T are complements) and G forms H bonds with C (G and C are complements).
In the example shown here:
one strand
the other strand
5’-T-G-3’
3’-A-C-5’
The two strands of nucleic acid are complementary in base sequence and also antiparallel or of
opposite orientation with respect to 5’  3’.
OK – now on to the process of transcription, continuing with our reading analogy…
In transcription you take the information that is contained in the sequence of the nucleotide bases
in DNA and copy (transcribe) that information into a sequence of nucleotide bases in RNA.
If you were to copy chapter 8 of the textbook you would need: the chapter, a pen, and knowledge
of letters, sentence structure, and punctuation.
To copy DNA nucleotides into RNA nucleotides you need: a DNA template (the chapter), an
RNA polymerase (the pen), and RNA nucleotide bases (letters).
If we show a strand of template DNA bases like this:
5’-A-C-G-T-T-C-G-T-A-A-C-G-G-G-C-T-A-3’
The RNA copy of this will be complementary in base sequence and opposite in orientation. The
RNA copy will be:
3’-U-G-C-A-A-G-C-A-U-U-G-C-C-C-G-A-U-5’
(remember that there is no T nucleotide base for RNA; have to complement A with U).
BIO 208 Unit 3 - Microbial Genetics and Viruses
Copying is facilitated by RNA polymerase. The RNA polymerase is a very large enzyme that
binds to the DNA molecule. It physically interacts with the DNA and catalyzes the hydrogen
bond formation between a DNA base on the DNA template strand and an RNA base on the
newly forming RNA copy (RNA transcript).
DNA is a huge polymer with hundreds of thousands of nucleotides. Some of the base sequences
carry the information for making functional products (tRNA and rRNA molecules or proteins).
These nucleotide base sequences in DNA that code for functional products are called genes
(genes would be analogous to sentences).
To use a reading analogy:
gdghfgffahThecatsatonthemat.gfdgffdflydlfy
Look at this string of letters – do you see a sequence that has meaning? (a sentence?)
If I asked you to copy the sentence, how do you know where to start? The capital letter indicates
the start of the sentence. In an analogous fashion, a gene will be copied into RNA when the RNA
polymerase interacts with a specific informational sequence in the DNA that says “bind to the
DNA here and then move away from this spot catalyzing the pairing of RNA bases to DNA
bases” – this informational sequence (capital letter) is the promoter.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Fig. 8.8
RNA nucleotides pair
with complementary DNA
nucleotides on the DNA
template strand
Fig. 8.8
5’-P
RNA polymerase continues
along the template DNA,
making RNA
How did you recognize the end of the sentence? The period. As the RNA polymerase continues,
eventually it will reach an informational sequence of nucleotides in the DNA that it will
recognize as instructing – “unbind from the DNA” (this causes transcription to stop and the RNA
copy will be released) – the informational sequence in the DNA is called the terminator.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
In the process of transcription the cell converts the information coded by the sequence of bases in
DNA into a complementary sequence of RNA bases (an RNA transcript, shown below).
3’-OH
5’-P
Now, information from DNA is
in the RNA molecule
If the DNA coded for tRNA and rRNA, then the transcript is cut and the tRNA and rRNA are
released.
If the DNA codes for protein, then the information carried in the sequence of RNA nucleotides
(a mRNA) must be translated into a sequence of amino acids. Because we are changing
“languages”, moving from a language of nucleotides to a language of amino acids, this process is
called translation. (just as moving from English to French is translation).
The process of translating information from RNA nucleotides to amino acids will require the
mRNA (the copy of the original document), the genetic code (a translational dictionary), the
tRNA carrying the amino acid (a translator), and the ribosome (a writing desk; a place to actually
do the work).
Let’s break out these elements:
mRNA – the information that was originally in the sequence of DNA nucleotide bases is
temporarily carried in the sequence of the RNA nucleotide bases. During translation, the RNA
bases will be read as 3 together (in triplets) from the 5’ to the 3’ direction. Each triplet of RNA
nucleotide bases is called a codon.
AU G
5’
3’
codon
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BIO 208 Unit 3 - Microbial Genetics and Viruses
tRNA is the translator – each tRNA molecule carries one of the 20 amino acids attached to its 3’
end. About midway along the sequence of nucleotides in tRNA are 3 bases that are
complementary to the codon – this base sequence in tRNA is called the anti-codon.
(tRNA is a single-stranded RNA molecule
but as it folds back on itself H bonds can
form between complementary bases giving
the tRNA a stable secondary structure.)
When the anti-codon of the tRNA base pairs with the codon of the mRNA, this brings in the
amino acid that corresponds to the codon of the mRNA. So the tRNA translates the codon in the
mRNA into an amino acid.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
(look at this codon 5’GCC 3’ and how it codes for the amino acid alanine (Ala). Now look at the
picture of the tRNA on the previous page. See how it carries alanine on its 3’ end and how the
anti-codon is complementary to the codon – that’s how the pairing of codon with anti-codon
ultimately matches the correct amino acid to a codon in the mRNA)
There are 4 nucleotide bases
a codon is made up of 3 bases
therefore there are 64 (43) different codons possible
but there are only 20 amino acids
In some cases multiple codons code for the same amino acids – Ex. The amino acid leucine is
coded for by 6 different codons in mRNA. This is called degeneracy in the genetic code and it
allows for some mutations in the nucleic acid to occur without changing the corresponding
protein.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Amino acids are physically linked together to form proteins on the ribosomes, which are located
throughout the cytoplasm.
Ribosomes are complex structures composed of proteins and rRNA.
At the beginning of translation of mRNA into protein, mRNA, tRNA carrying amino acid, and
ribosome subunits are moving freely in the cytoplasm.
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On the mRNA is a specific codon called the start codon that will orient the process of translation.
The start codon always has the sequence 5’-AUG-3’. The ribosome subunits will come together at
the start codon and a tRNA with the anti-codon 3’-UAC-5’ will enter the ribosome and will H bond
with the codon on the mRNA. This tRNA will be carrying the amino acid methionine (or
formylmethionine in Bacteria).
Translation will now proceed from this point on the mRNA, the ribosome will physically move
along the mRNA, to the right, one codon at a time, translating the RNA nucleotide bases into
amino acids, and the protein chain will grow.
End Review
BIO 208 Unit 3 - Microbial Genetics and Viruses
Unit 3 Microbial Genetics and Viruses
Lectures 14-16 we will examine how information flows in the microbial world.
I. Patterns of Information Flow in the Microbial World Fig. 8.2

Within one organism (cell)

From one organism to another:
o from one generation to the next (vertical transfer)
o between cells of the same generation (horizontal transfer)
A. Basic genetics review:
1. Structure of nucleotides and nucleic acids
Nucleotides are
composed of 3 basic parts (label drawing on next page):
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Base
O
C
O
O
P
O
O
P
O
O
P
O
O
O
H
H
H
3 phosphates
= triphosphate
O
N
C
C
C
O
O
C
N
C
C
C
C
O
O
H
H
5 carbon sugar
= ribose
Fig. 2.17 - modified
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BIO 208 Unit 3 - Microbial Genetics and Viruses
The base of a nucleotide can be one of 5 kinds:
Adenine –
Guanine –
Thymine –
Cytosine –
Uracil –
A nucleic acid is a
There are 2 kinds of nucleic acids:
1. RNA – Ribonucleic acid
Sugar Bases 3 kinds of RNA molecules:
transfer RNA (tRNA)
messenger RNA (mRNA)
ribosomal RNA (rRNA)
RNA molecules are generally
2. DNA – deoxyribonucleic acid
Sugar Bases –
DNA molecules are generally
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BIO 208 Unit 3 - Microbial Genetics and Viruses
A nucleic acid is a polymer of nucleotides. (shown with DNA nucleotides):
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Nucleotides continue to be added until a long polymer is formed:
H3C
H
H
H
H
Notice a couple things about this polymer:
1.
2.
3.
4.
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The sequence of the nucleotide bases in a nucleic acid has meaning. The S-P backbone is constant, the
same in all DNA molecules.
**It is the sequence of the nucleotide bases that carries the information.
Base pairing -
In the example shown here:
BIO 208 Unit 3 - Microbial Genetics and Viruses
Joining of nucleotides to make a nucleic acid
Fig. 8.4
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BIO 208 Unit 3 - Microbial Genetics and Viruses
The two strands of nucleic acid are complementary in nucleotide base sequence and also
antiparallel or of opposite orientation with respect to 5’  3’.
Fig. 8.3b
The 2 strands twist around each other to form a double helix
The double helix of DNA has to be organized and packed to fit inside the cell. Fig. 8.1a
In all cells, DNA is organized into chromosomes, but the size of the DNA molecule, the number,
structure, and packaging of the chromosome varies among the 3 Domains:
how many base pairs are in the DNA?
how many chromosomes does cell have?
what is the structure of chromosome?
how is chromosome packed to fit in cell?
Archaea
5 x 105 to 5 x 106
1
closed circle
histones,
nucleosome-like
Bacteria
2 x 106
1
closed circle
supercoiling,
DNA binding
proteins
Eukarya
1 x 107 and more
many
linear
histones,
nucleosomes,
chromatin
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BIO 208 Unit 3 - Microbial Genetics and Viruses
B. Flow of information from one generation to the next ( = vertical transfer)
1. Overview DNA Replication (repl.) (pp. 212-216)
DNA replication is semiconservative – resulting ds DNA after replication is made up of 1
old strand of DNA and 1 new strand of DNA.
Fig. 8.3
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BIO 208 Unit 3 - Microbial Genetics and Viruses
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Fig. 8.5 Review of DNA replication - Events at the DNA Replication Fork
1. Notice the orientation of each of the strands of DNA
2. Enzymes (helicases) unwind the parental double helix
3. Proteins stabilize the unwound, single stranded parental DNA (otherwise it would just re-pair
and coil back up)
4. DNA polymerase catalyzes the addition of new nucleotides to the new strand
5. DNA polymerase can only add nucleotides to an exposed 3’OH
6. The new strand of DNA is synthesized with the new strand extending in a 5’ to 3’ direction.
7. But what about the other strand, how is it copied?
8. The other strand has no exposed 3’OH so DNA polymerase cannot act
9. But RNA polymerase does not need an exposed 3’OH in order to add nucleotides
10. RNA polymerase brings in complementary RNA nucleotides to make a short section of RNA
called a “primer”
11. These RNA primers have exposed 3’OH so now DNA polymerase can work.
12. DNA polymerase adds nucleotides causing the new strand to grow in a 5’ to 3’ direction (as on
the other strand).
13. Synthesis on this strand is discontinuous, not continuous as on the other strand.
14. Discontinuous synthesis, because there are more steps, is slower.
15. The synthesis on this strand will lag behind, so this strand can be called the “lagging strand”, the
other strand can be called the “leading strand”.
16. Eventually, on the lagging strand, the DNA polymerase will run into the back of an RNA primer.
17. The DNA polymerase removes the RNA nucleotides and replaces them with DNA nucleotides.
18. Another enzyme called DNA ligase joins the fragments of the lagging strand.
BIO 208 Unit 3 - Microbial Genetics and Viruses
Summary – 3 enzymes are involved in DNA replication:
1.
2.
3.
2. DNA replication in Bacteria Fig. 8.6
Origin of replication –
2 repl. forks form.
Bidirectional –
**Consequences –
DNA replication in Archaea -
C. Flow of information within a single cell
**DNA contains sequences of nucleotide bases that code for functional products – these
sequences are called genes.
Gene –
Functional products may be:
Structural RNAs
Proteins
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BIO 208 Unit 3 - Microbial Genetics and Viruses
1. Transcription (transc.) (p. 216)
Transc. will require:
 DNA template
 RNA nucleotides
DNA template sequence (of nucleotide bases)
5’-A-C-G-T-T-C-G-T-A-A-C-G-G-G-C-T-A-3’
The RNA copy of this

The enzyme RNA polymerase (RNA pol) – A large DNA binding protein whose job is
to catalyze the addition of RNA nucleotides. The RNA polymerase of Archaea is more
similar to the RNA polymerase of Eukarya than to the RNA polymerase of Bacteria.

2 kinds of informational DNA nucleotide sequences:
Promoter –
Terminator –
DNA
Initial
binding site
Pribnow
sequence
Promoter
First nucleotide
transcribed
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Review the process of transcription Fig. 8.7
The orientation of the RNA copy (= the transcript) produced is complementary and antiparallel to the template DNA.
The RNA transcript may be:
ribosomal RNA (rRNA)
transfer RNA (tRNA)
messenger RNA (mRNA)
What happens next to the RNA transcript? – is the transcript modified after it is made? (called
post-transcriptional modification)
rRNA / tRNA molecules
mRNA
Bacteria and Archaea
modified
not modified
Eukarya
modified
extensively modified
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BIO 208 Unit 3 - Microbial Genetics and Viruses
2. Translation (transl.) (pp. 217-221)
How does the information contained in RNA get passed on to proteins? Translate the
information carried in the sequence of nucleotide bases of the mRNA and use that
information to build a protein (a protein is a polymer of amino acids).
Transl. will require:
 mRNA –
 genetic code
 tRNA  rRNA mRNA
AU G
5’
3’
codon
codon –
tRNA – the translator –
anticodon -
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mRNA codon sequence
5’
3’
Consensus sequence -
There are similarities and differences among the 3 Domains what the transl. start is
Transl. start
1st aa
Bacteria
1 mRNA  several
proteins (operon)
consensus sequence
N-formylmethionine
Archaea
1 mRNA  several
proteins
consensus sequence
Methionine
1st a.a. – the first amino acid in the newly formed protein.
Eukarya
1 mRNA 
1 protein
5’-P end of mRNA
Methionine
BIO 208 Unit 3 - Microbial Genetics and Viruses
Ribosomes are complex molecules composed of rRNA and proteins. Ribosomes will selfassemble on the mRNA molecule.
Subunit sizes
rRNA sizes
# of proteins
Complete ribosome
Bacteria and Archaea
50S
30S
16S*
5S
23S
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Eukarya
60S
40S
18S*
5S
5.8S
28S
82
70S
80S
Remember that S stands for “Svedberg”, which refers to how the molecule moves in a
centrifugal force.
* it was the DNA coding for these rRNA that Carl Woese sequenced to discover the 3
Domains of Life.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
Review the process of translation - Fig. 8.9, 8.8
Summarizing where transcription and translation happen in the 3 Domains and what the
consequences of where are.
Bacteria and Archaea
Eukarya
Site of transcription
cytoplasm
nucleus
Site of translation
cytoplasm
cytoplasm
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BIO 208 Unit 3 - Microbial Genetics and Viruses
3. Gene Expression and Regulation
In Eukarya the mRNA transcript is formed in the nucleus and then leaves the nucleus,
traveling to the ribosomes in the cytoplasm.
**In Bacteria and Archaea – transcription and translation both occur in the cytoplasm –
this means that transcription and translation occur simultaneously.
Expression –
Eukarya regulate gene expression by regulating whether or not translation occurs (an
event physically separated from transcription in the cell).
Regulation of gene expression in Bacteria and Archaea - happens by regulating whether
or not transcription occurs. (pp. 221-226).
Bacteria have 2 kinds of genes:
Constitutive –
Ex. Genes for enzymes necessary to break down glucose
Inducible –
Ex. Genes for enzymes to break down lactose
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BIO 208 Unit 3 - Microbial Genetics and Viruses
**Example of regulation of inducible genes - Lactose Operon of E. coli
Operon –
1. Structure of lac operon of E. coli
Fig. 8.12 modified
a. 3 Structural genes - encode enzymes
Gene
Enzyme
Z
-galactosidase
Y
Lactose permease
A
Transacetylase
b. A promoter and an operator
promoter operator –
c. I gene –
RNA polymerase also involved
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2. How does E. coli control expression of these genes?
a. If have glucose but no lactose – don’t want structural genes for lactose use to be expressed.
I gene is transc. & transl. into repressor protein that binds to DNA at the operator
region – physically blocks the movement of the RNA polymerase so the structural
genes are NOT expressed.
BIO 208 Unit 3 - Microbial Genetics and Viruses
b. If there is no glucose but there is lactose:
I gene is transc. & transl. into repressor protein, as above. But lactose is transported
into cell where it is converted into allolactose (which is called an inducer) –
allolactose binds to the repressor protein. Now the repressor protein can’t bind to the
operator sequence. The RNA polymerase is not blocked. The structural genes are
expressed and the 3 enzymes needed to breakdown lactose are made.
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D. Flow of information from one cell to another cell of the same generation
**Flow of information between cells of the same generation (called horizontal gene transfer =
HGT) (pp. 233-241)
**Unlike Eukarya, which evolve principally through the modification of existing genetic
information, Bacteria and Archaea have obtained a significant proportion of their genetic
diversity by taking genetic material directly from distantly related organisms.
Importance of HGT:
•
•
•
•
May account for 10 to 50% of all the genes in the genome of a Bacteria or Archaea.
Has occurred between diverse species and even across the boundaries of Domains (e.g.,
Bacteria have acquired genes from Eukarya).
Produces extremely dynamic genomes in which substantial amounts of DNA are introduced
into and deleted from the chromosome.
Has led to the emergence of new pathogenic microbes.
How do microbes of the same generation exchange DNA?
Overall process involves:
Recombination –
Recombination always requires:
Donor –
Recipient –
Recombinant
BIO 208 Unit 3 - Microbial Genetics and Viruses
**3 Mechanisms of Horizontal Gene Transfer (HGT)
1. Transformation – DNA released by one bacterium (naked DNA) is taken up by a 2nd
Fig. 8.25
Ex. Streptococcus pneumoniae -
2. Conjugation – DNA transfer is mediated by a plasmid (plasmid ntroduced in Unit 1)
Conjugation requires direct cell to cell contact via a pilus (pilus introduced in Unit 1)
Fig. 8.27
Examples:
Pseudomonas –
Clostridium tetani –
Bacillus anthracis –
Many, many antibiotic resistance
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BIO 208 Unit 3 - Microbial Genetics and Viruses
3. Transduction – bacterial DNA is transferred from donor to recipient inside a virus that
specifically infects bacterial cells (a bacteriophage or phage; more about these later in
this Unit)
Fig. 8.28
Examples:
Corynebacterium diphtheriae –
Streptococcus pyogenes –
E. coli O157:H7 –
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BIO 208 Unit 3 - Microbial Genetics and Viruses
II. Viruses (Ch. 13)
Lectures 17-19 - we will discuss viruses, with an emphasis on viruses that affect humans:
A. General Characteristics of Viruses
1. Origin and Evolution – where did they come from? The main theories:
a. Descendants of primitive pre-cellular life forms (free-living facultative 
obligate parasite.
b. Degradation of cells of ancient origin & co-evolved w/ host organisms
2. Distinctive features of viruses
a. nucleic acid (na) –
b. protein coat –
envelope –
c. multiply inside living cells using machinery of host
d. cause the synthesis of specialized structures that can transfer viral na to other cells
3. Host range – range of species whose cells a virus may infect (Ex. polio virus infects
humans, not fruit flies) - determined by attachment
a. animal cells – receptor for virus
Tissue Tropism – the cells of which tissue a virus will infect (Ex. within humans, polio
virus infects cells of intestines and nervous tissue, but not liver) – also determined by
attachment
b. bacteria – receptor for virus
4. Sizes (Fig. 13.1)
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BIO 208 Unit 3 - Microbial Genetics and Viruses
B. Viral Structure - view w/ EM (pp. 370-373)
1. Virion –
2. Nucleic acid –
3. Capsids and envelopes
capsid –
capsomeres –
envelopes –
naked vs. enveloped
spikes –
Ex. Hemagglutinin of Influenzavirus
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BIO 208 Unit 3 - Microbial Genetics and Viruses
4. Morphology - used in classification
a. helical –
capsid is helical
na is helical
Ex.
b. polyhedral –
capsid is icosahedron
20 triangles
12 corners
na is packed within
Ex.
c. complex
Ex. bacteriophages
5. Taxonomy
a. Family: -viridae
Ex. Herpesviridae
b. Genus: -virus
Ex. Simplexvirus
c. Species - group of viruses sharing genetic information and ecological niche
d. Common names
Simplexvirus
herpes simplex virus
HSV
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BIO 208 Unit 3 - Microbial Genetics and Viruses
C. Viral Multiplication
1. Bacteriophages
a. Lytic cycle – results in lysis and death of infected host bacterium
Ex. T-even in E. coli
b. Lysogenic cycle – the infected host remains alive
Ex. bacteriophage lambda () in E. coli
Lytic and lysogenic cycles (Fig. 13.11, 13.12)
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BIO 208 Unit 3 - Microbial Genetics and Viruses
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3. Animal Viruses (pp. 382-389); Fig. 13.19
a. attachment to receptors on host plasma membrane
b. penetration – 2 mechanisms
i. pinocytosis (also referred to as endocytosis) – host plasma membrane actively
engulfs and internalizes the entire virus
ii. fusion – viral envelope fuses with host plasma membrane, only viral na enters cell
c. uncoating –
d. transc. of some viral genes followed by their transl. using the host RNA pol.
Genes transc. and transl. are enz. nec. for viral DNA repl.
e. replication of viral nucleic acid – will depend on the type of na the virus has
DNA viruses – may have either ss or ds DNA molecule. In either case, DNA is
repl. in nucleus of host cell using enz. encoded by the virus.
RNA viruses – gets more complicated. The viral RNA can be similar to a mRNA,
in which case it is called a sense strand or a (+) strand. Or it can be opposite in
orientation to a mRNA, in which case it is called an antisense strand or a (-) strand.
Some RNA viruses are ss and will have either a (+) strand or a (-) strand. If they
have a (-) strand RNA they must first complement this RNA and create a (+) strand
to serve as a mRNA using a special RNA pol that can read an RNA template
(rather than a DNA template). There are also viruses that are ds RNA having 1 (+)
and 1 (-) RNA. Finally there are Retroviruses. Retroviruses will copy their RNA
genome into a DNA copy using an enz. called reverse transcriptase.
BIO 208 Unit 3 - Microbial Genetics and Viruses
f. transcription & translation (expression) of viral capsid proteins using a true mRNA or
a (+) RNA and the protein synthesis apparatus of the host cell
g. assembly of virions
h. release of mature virions
i. lysis ii. budding -
i. effects of viruses on animal cells (not in your text)
a. lytic Ex
b. persistent – slow shedding over long periods of time
Ex.
c. latent – dormant and then triggered
Ex.
d transformation –
Ex.
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BIO 208 Unit 3 - Microbial Genetics and Viruses
D. Working with Viruses in the Lab (not in your text)
Biosafety Levels (BL)
BL1 – no disease risk – general lab safety protocols; lab coats, handwashing
BL2 – moderate potential health hazards – training, sign posting, eyewear, gloves, masks
BL3 – serious high individual risk – high level training, vaccinations, clean suits,
respirators, UV lights
BL4 – lethal, no vaccines or treatments – fully protective suits, airlocks, decontamination
showers
U.S. BL4 Units
1. Centers for Disease Control and Prevention (CDC)
2. US Army Medical Research Institute of Infectious Disease (USAMRID)
3. National Institutes of Health (NIH)
4. Southwest Institute for Biomedical Research
video
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BIO 208 Unit 3 - Microbial Genetics and Viruses
E. Brief survey of viruses and viral infections
1. DNA Viruses 4 families to know
a. Papovaviridae (p, 385) - ds, nonenveloped
 Include viruses that cause warts
 More than 50 types
 Genital warts = #1 STD - epidemic - 500,000 new cases every year
 Associated with cancer of cervix and penis
b. Poxviridae (p. 385) - ds, enveloped
 Orthopoxvirus - smallpox, cowpox, monkeypox
 Smallpox - humans only, ancient
 Immunization history
 Eradication of smallpox
 Gone but not gone
o Bioterrorism
o Changing ecology of pox viruses
 Monkeypox
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BIO 208 Unit 3 - Microbial Genetics and Viruses
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c. Herpesviridae (p. 385)- ds, enveloped
 Nearly 100 known, include viruses that cause cold sores, genital herpes,
chickenpox, and infectious mononucleosis (mono)
 Latency
 No cure - "Herpes is for Life"
i. Herpes - Simplexvirus - transmitted by direct contact
o HSV-1 (or HHV-1)- cold sores, fever blisters - 90%
o Wrestlers
o HSV-2 (or HHV-2) - sexually transmitted
ii. Chickenpox - Varicellovirus (HHV-3)
o 3rd most common reportable infectious disease in U.S.
o Transmitted by aerosol or by direct contact
o High morbidity but low mortality
o Reactivates as shingles
o Vaccine approved in 1995
iii. Epstein-Barr Virus (EBV) - Lymphocryptovirus (HHV-4)
o Infectious mononucleosis (mono)
o Developing countries vs U.S.
o Burkitt's lymphoma and relationship to malaria
d. Hepadnaviridae (p.386)- ds, enveloped
 Hepatitis B virus - transmitted by blood, needles (incl. Tattoo needles), saliva,
sexual contact - can survive up to 1 week in dried fluids.
 100X more contagious than HIV
 Hepatitis - inflammation of the liver - 2nd most commonly reported infectious
disease in the U.S.
 300,000 young adults infected each year
 5,000 deaths each year
 Symptoms - loss of appetite, low-grade fever, joint pain, later jaundice
 10% chronic carriers (1 million U.S.) - associated with liver disease, incl. cancer
 Vaccine - 3 shots
BIO 208 Unit 3 - Microbial Genetics and Viruses
2. RNA viruses – 6 families to know
a. Picornaviridae (p.387) - ss, positive (+) strand, no envelope
i. Enterovirus - acquired by ingestion, replicate in the intestinal tract.
 Include poliovirus – ancient  Vaccine developed in 1950s and 1960s
 Worldwide eradication predicted
ii. Rhinovirus - common cold
 Transmitted by aerosols, direct contact
 More than 100 strains
 Incubation period is 24 hours
 No effective treatment
iii. Hepatitis A virus - hepatitis
 Acquired by ingestion of contaminated food (oysters) and water
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BIO 208 Unit 3 - Microbial Genetics and Viruses
b. Flaviviridae (not in text) – ss, (+) strand, enveloped
 Includes Yellow Fever, Dengue, West Nile
 All are vector-borne (mosquitoes, etc)
 West Nile – Uganda 1957, U.S. 1999
 Includes Hepatitis C virus - hepatitis
c. Coronaviridae (not in text) – ss (+) strand, enveloped
 Includes SARS-CoV – Severe Acute Respiratory Syndrome
 Newly evolved strain, 1st appeared in China in 2002
 Spread in large respiratory droplets
d. Filoviridae (not in text) - ss, negative (-) strand, enveloped
 Includes Marburg and Ebola  Indigenous to Africa, but not confined to Africa
 Natural host e. Orthomyxoviridae (not in text) - (-) strand RNA, segmented
 Includes - Influenzavirus - the flu f. Retroviridae (p.387) - RNA viruses that produce DNA using the enzyme reverse
transcriptase, enveloped
 Includes Lentivirus or HIV
F. Prions - Proteinaceous Infectious Particles (pp. 392-393)
A normal host cellular protein is refolded incorrectly, becoming abnormal and infectious
 Scrapie (sheep)
 Kuru (humans)
 Creutzfeldt-Jacob Disease (CJD) (humans)
 Bovine Spongiform Encephalopathy (BSE = mad cow disease; nvCJD in humans)
So, what am I to know about viruses?
1. Describe the physical structure of an enveloped and a nonenveloped (naked) virus
2. Understand how viral families, genera, and species are named
3. Describe lytic and lysogenic cycles of bacteriophages
4. Know the steps in multiplication of animal viruses
5. Discuss the relationship of viruses to cancer
6. Provide examples of latent infections
***7. Know characteristics of the 10 virus families listed, including diseases
This ends the lecture material for Test 3.
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