Transcript Chapter 18

Chapter 18 - Genetics of Viruses and Bacteria
Questions
1. The proteins that encapsulate the genetic material of
a virus is known as the _____________.
2. Draw a general structure of a eukaryotic virus and
label
3. An parts.
individual protein of the structure mentioned in
question number 1 is known as a _______________.
4. A bacteriophage can reproduce via two different life
cycles known as the ________________ and
_________________.
5. The genetic material of viruses can be ______,
______, _____ or ______.
6. This general structure is found to be part of some
viruses like Influenza and not part of other viruses like
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Viruses : Packaged Genes
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
What is a virus?
1. Obligate intracellular parasite
- A small [20 to 250nm in diameter]
infectious agent that requires a host
cell to replicate (make more of itself).
**1/1000th the diameter of a
eukaryotic cell. If the classroom was
a cell, a virus would be about the size
of a paperclip.
2. General Structure
Nucleic acid enclosed in a protein coat
and, in some cases, a membranous
envelope
3. Host Range
- Each virus can only infect a specific
range of cell types
Ex. HIV can only infect CD4+ Helper T-
SEM of adenovirus
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Size Comparison
Virus: 20 to 250nm (.02 to
.25um
)
Prokaryote:
1 to 10um
Eukaryote: 10 to 100um
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
CAPSID
1. All viruses contain genetic material (DNA or RNA) encapsulated by a protein coat called a capsi
2. An individual protein in the capsid is called a capsomere.
3. Bacteriophage (phage) have the most complex capsids
Capsomere
of capsid
Membranous
envelope
RNA
Capsomere
DNA
Head
RNA
18
Glycoprotein
70–90 nm (diameter)
250 mm
20 nm
50 nm
(a) Tobacco mosaic virus (b) Adenoviruses
DNA
Tail
Capsid sheath
Glycoprotein
80–200 nm (diameter)
50 nm
(c) Influenza viruses
Tail
fiber
80
225 nm
50 nm
(d) Bacteriophage T4
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Influenza looks different…it has an envelope. What’s up with
that?
Capsomere
of capsid
Membranous
envelope
RNA
Capsomere
DNA
Head
RNA
18
Glycoprotein
70–90 nm (diameter)
250 mm
20 nm
50 nm
(a) Tobacco mosaic virus (b) Adenoviruses
DNA
Tail
Capsid sheath
Glycoprotein
80–200 nm (diameter)
50 nm
(c) Influenza viruses
Tail
fiber
80
225 nm
50 nm
(d) Bacteriophage T4
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Envelopes
1. Only some viruses have cell membrane-like
envelopes
Membranous
envelope
Capsid
RNA
Ex. Influenza (shown right)
2. The envelope is derived (comes from) the
cell membrane of the host cell
Glycoprotein
80–200 nm (diameter)
50 nm
(c) Influenza viruses
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
How do viruses replicate (reproduce)?
Viruses Hijack Cells
They gain access and use the
enzymes, ribosomes, and small
molecules (ATP, nucleotides, amino
acids, phospholipids, etc…) of host
cells.
Simplified viral reproductive cycle
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
Let’s begin with the best understood virus:
T4 Phage infecting E. coli
1. Bacterial virus (bacteriophage or just
phage)
How do they reproduce?
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Fig. 10.17
Bacteriophage
reproductive
cycle
(two
methods of reproduction)
Bacteriophage binds to the surface of the
bacterium using the tail fibers and injects its
DNA into the cell…
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Fig. 10.17
Bacteriophage
reproductive
cycle
(two
methods of reproduction)
Lysogenic cycle
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Bacteriophage
reproductive
cycle
(two
Fig. 10.17
methods of reproduction)
Lytic cycle
Lysogenic cycle
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Lysogenic cycle
- After the bacteriophage injects its DNA, it might get incorporated into the
bacterial chromosome and is now called a prophage. Now when the
bacterial cells replicates, the phage DNA replicates with it.
Lytic cycle
- After the bacteriophage injects its DNA or when the prophage jumps out of
the DNA, it can hijack the cell and use it (its ribosomes and other enzymes)
to make more viral DNA and proteins to in turn make more viral particles.
The cell will lyse and the viruses will be released.
Temperate Phages
- Phages that can do both lytic and lysogenic methods of reproduction
Ex. Lambda (λ) phage
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
What causes a temperate phage like lambda to switch from
lysogenic to lytic?
We observed the switch to be caused by environmental factors like radiation or
certain chemicals causing DNA damage, which would promote the lytic phase
as the bacterial cell will likely die soon and the phage needs to get out quick.
In addition, lytic is favored when nutrients are plentiful allowing the phage to
makes lots more of itself, while the lysogenic is favored when nutrients are in
low concentration within the bacterium. This makes sense as the virus can lay
low until better times. Can’t make more of yourself if the materials are simply
Chapter 18 - Genetics of Viruses and Bacteria
NEW AIM: Viruses: Packaged Genes…
Can prokaryotes defend themselves against this attack?
Of course. They contain enzymes that attempt to hydrolyze the viral DNA known as
restriction enzymes like little molecular scissors.
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
A. Anatomy
Genetic Material – Can be ssDNA/dsDNA or ssRNA/dsRNA depending on the
virus. Codes for polypeptides/proteins needed by the virus to enter and hijack
the cell as well as the proteins of the capsid and envelope.
Capsid – made of proteins and surrounds the genetic material in the core.
Envelope – Phospholipid bilayer similar to a cell membrane with embedded
proteins (protein spikes) surrounding the capsid. Not all virus types have
envelopes
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
DNA
Capsid
Protein
spikes
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
They are classified by their genetic material.
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
DNA viruses
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
DNA
capsid
envelope
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
Ex. Adenovirus
- Causes upper respiratory
- Symptoms range from those
infections
similar to the common cold to
bronchitis or pneumonia.
(Common cold is caused by rhinovirus, an RNA virus)
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
Ex2. Herpesviruses (family of related viruses)
These can cause:
1. Oral herpes (cold sores) or genital herpes
(an STD)
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
Ex2. Herpesviruses (family of related viruses)
These can cause:
2. Chicken pox (varicella zoster virus)
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
Ex3. Poxvirus (family of related viruses)
Can cause:
1. Small pox
This is the only human infectious
disease to ever be eradicated
(removed from the face of the planet)
– we did this through extensive
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
Ex4. HPV – Human Papillomavirus
A. Over 200 different types…many are STDs (sexually
transmitted)
1. Some of these STD viruses can lead to cancers of the
cervix, vagina, and anus in women or cancers of the
anus and penis in men.
a. Nearly all cases of cervical cancer are caused by HP
2. Others cause genital warts
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
B. DNA viruses
HPV Vaccine
Recommended by CDC for all females and males age 11 to
26.
http://www.nytimes.com/2011/10/26/health/policy/26vaccine.html
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
What do viruses need to
accomplish to continue to exist?
1. Gain access to a cell
2. Use the cell’s workers (ribosomes, RNA
polymerase, etc…) to make more of itself.
a. Synthesize viral proteins
b. Replicate its genome
c. Assemble these into new viral particles
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
What is the first thing a virus
must be able to do?
1. Viral Attachment and Entry
a. If the virus does not have an
envelope, protein spikes on the
capside will act as ligands and
bind cell receptors, triggering
receptor mediated endocytosis.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
1. Viral Attachment and Entry
b. If it does have an envelope,
the protein spikes in the
envelope will act as ligands and
bind to cell receptors resulting in
fusion of the viral membrane and
cell membrane, injecting the
capsid into the cell…
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
1. Viral Attachment and Entry
Analogy:
Cell receptors = door lock
Protein spikes = the key
In either case, the protein spikes
on the surface need to bind
receptors to gain access to the
cell, which is why specific viruses
can only infect specific cells with
matching receptors.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
A. Viral attachment and entry
B. Uncoating
The capsid fall apart and
the viral DNA enters the
C.nucleus
Transcription and
translation of the viral DNA
The viral DNA is transcribed and
translated by our workers (our
RNA polymerases,
ribosomes/tRNAs/etc…) using
our ATP made by our
mitochondria!!
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
D. Replication of the viral DNA
E. Viral protein sorting
Capsid proteins are brought
into the nucleus while
envelope proteins get into
nuclear membrane via
endomembrane system.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
F. Viral assembly
Capsid forms around DNA
and then buds out of
nucleus picking up its
H.envelope
Release
How the virus, now in the
cytoplasm, gets out of the
cell is not understood yet.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Life cycle of a DNA
virus
This process typically
happens over and over and
over again until the cell
dies…The cell is a virus
producing factory.
DNA integration
In certain viruses, like Herpes virus, the
viral DNA can integrate (become part
of) the cell’s DNA (your DNA), and sit
quietly similar to the lysogenic cycle of
bacteriophages. Almost all adults carry
Herpes Simplex 1 virus (oral herpes).
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
RNA viruses
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
Ex1. Mumps virus
- Member of the paramyxovirus family
- Causes the mumps
Extreme swelling of salivary glands
Before infection
Contagious via respiratory
secretions
(coughing/sneezing/sharing
After infection glass/kissing/etc…)
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
Ex2. Rubella virus
- Member of the togavirus family
- Causes rubella (German measles)
Rash on body
Flu-like symptoms
Highly Contagious
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
Ex3. Measles
- Caused by a member of the
paramyxovirus family like mumps
- Highly contagious through
respiratory secretion just like
mumps
Symptoms: Rash on body,
cough, runny nose, red eyes, four
day fevers
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
If these viruses are so
easily contagious, why
haven’t you gotten
them?
You have all been vaccinated against them
(MMR shot)
MMR = measles, mumps, rubella
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
Ex4. Poliomyelitis (polio)
- Highly contagious through
fecal-oral route (feces to the
mouth)
It is easier than you think…the chef
prepares your food and didn’t wash
- Inhis
1%hands
of infections, virus enter
neurons and destroys motor
function – lose control of your
muscles
You are vaccinated against this
one too…
Animal RNA virus life cycle
1. Viral attachment and
entry
Similar to DNA virus – protein
spikes act as ligands for cell
receptors.
2. Uncoating
Capsid falls apart releasing the
3. RNA
RNA synthesis
A viral enzyme will make the
complementary RNA strand
(purple) using the genomic RNA
(red) as a template
4. Protein synthesis
Complementary RNA can act as
mRNA and your ribosomes will
translate it, making new viral
proteins.
Fig. 10.18a
Animal RNA virus life cycle
5. Synthesizing more genomic RNA
The complementary strand (purple)
can also act as a template to back
synthesize the more genomic RNA
(red)
6. Assembly
The viral proteins and genomic
RNA come together to make
new viral particles.
Some of the viral proteins made were
sent through the endomembrane
system to the cell membrane.
Fig. 10.18a
Animal RNA virus life cycle
7. Exit
The capsid/RNA pinch off from the
cell, which is how it acquires the
envelope with embedded viral
proteins.
-Notice that the nucleus is not
involved.
-This process happens again
and again until the cell is dead.
-There can be no integration of
standard RNA viruses into our
genome as RNA cannot be
integrated into DNA
Fig. 10.18a
The reproductive cycle of an enveloped RNA virus
1 Glycoproteins on the viral envelope
bind to specific receptor molecules
(not shown) on the host cell,
promoting viral entry into the cell.
Capsid
RNA
Envelope (with
glycoproteins)
2 Capsid and viral genome
enter cell
HOST CELL
Viral genome (RNA)
Template
5 Complementary RNA
strands also function as mRNA,
which is translated into both
capsid proteins (in the cytosol)
and glycoproteins for the viral
envelope (in the ER).
3 The viral genome (red)
functions as a template for
synthesis of complementary
RNA strands (pink) by a viral
enzyme.
mRNA
Capsid
proteins
ER
Glycoproteins
Copy of
genome (RNA)
4 New copies of viral
genome RNA are made
using complementary RNA
strands as templates.
6 Vesicles transport
envelope glycoproteins to
the plasma membrane.
8 New virus
7 A capsid assembles
Figure 18.8
around each viral
genome molecule.
Chapter 18 - Genetics of Viruses and Bacteria
AIM: Viruses: Packaged Genes…
2. Animal viruses
C. RNA viruses
Ex5. Retrovirus
Ex. HIV (human immunodeficiency virus)– you
will need to know the details on this one
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Retroviruses
- A special family of RNA viruses
- Retro implies Reverse
- These viruses have an RNA genome, but use
a special enzyme called Reverse
Transcriptase to make a DNA copy of the RNA
(the reverse of transcription; hence the name)
Ex. HIV (human immunodeficiency virus)
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Retroviruses
Fig 10.21A
Attachment
protein is called
GP120
HIV
- Enveloped RNA virus
HIV
- Capsid houses two identical RNA molecules and the enzyme
Reverse Transcriptase as well as others needed for the virus to
function.
Why do you think the virus needs to carry its own Reverse
Transcriptase?
Because our cells do not have the gene for reverse transcriptase
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Retroviruses
HIV
How is HIV transmitted?
The virus is transmitted through
contact of a bodily fluid
containing HIV like blood, semen,
vaginal fluid, and breast milk with
a mucous membrane or the
bloodstream.
A. ~33 million people are HIV positive in the world.
B. Estimated 1.1 million people are HIV positive in the
US.
C. ~2.2 million people, 330,000 of which were children, died as a result of the virus
last year – 75% of deaths occurred in Sub-Saharan Africa.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Retroviruses
Fig 10.21A
HIV
What disease does HIV cause?
- AIDS – Acquired Immune Deficiency Syndrome
Immune system gradually declines leaving the individual
susceptible to opportunistic infections like tuberculosis (5 –
10% of Americans test positive for the bacterium that causes
tuberculosis, but the immune system keeps it in check and the
person is fine)and tumors (many cells that would have caused
cancer are destroyed by the immune system).
Therefore, HIV/AIDS does not kill anyone directly, it is the
opportunistic infection or cancer that kills the person.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Retroviruses
HIV
How does HIV cause AIDS?
HIV (blue dots) infects, hijacks and
in the end destroys Helper T-cells
(red) (special type of cell of the
human immune system required for
proper function).
Let’s look at how HIV infects Helper-T
cells…
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
HIV Life Cycle
GP120
Attachment and Entry: HIV envelope glycoprotein GP120 (ligand) binds to
the CD4 receptor on the surface of the Helper T-cell resulting in fusion of the
viral envelope with the cell membrane thereby allowing the capsid to enter
the cell and fall apart releasing the viral RNA and Reverse transcriptase
enzymes.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
HIV Life Cycle
This figure skips the “attachment
and entry” and “uncoating” of the
viral particle.
Fig 10.21B
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
HIV Life Cycle
1. Reverse Transcriptase makes
a DNA copy (blue) of the viral
RNA genome (red).
2. Reverse Transcriptase then
removes the RNA and
synthesizes the complementary
DNA strand.
3. Integration: the dsDNA enters
the nucleus and gets integrated
(inserted) into the DNA.
Fig 10.21B
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
HIV Life Cycle
4/5. Transcription/Translation:
viral RNA and proteins are
synthesized from the provirus
(analogous to prophage) DNA.
6. Assembly: viral particles are
assembled and bud off the cell
This process happens over and
over again as long as the Helper
T-cell lasts…
Fig 10.21B
The reproductive cycle of HIV, a retrovirus
HIV
Membrane of
white blood cell
1 The virus fuses with the
cell’s plasma membrane.
The capsid proteins are
removed, releasing the
viral proteins and RNA.
2 Reverse transcriptase
catalyzes the synthesis of a
DNA strand complementary
to the viral RNA.
HOST CELL
3 Reverse transcriptase
catalyzes the synthesis of
a second DNA strand
complementary to the first.
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
4 The double-stranded
DNA is incorporated
as a provirus into the
cell’s DNA.
0.25 µm
HIV entering a cell
DNA
NUCLEUS
Chromosomal
DNA
RNA genome
for the next
viral generation
Provirus
mRNA
5 Proviral genes are
transcribed into RNA
molecules, which serve as
genomes for the next viral
generation and as mRNAs
for translation into viral
proteins.
6 The viral proteins include
capsid proteins and reverse
transcriptase (made in the cytosol)
and envelope glycoproteins
(made in the ER).
Figure 18.10
New HIV leaving a cell
9 New viruses bud
off from the host cell.
8 Capsids are
assembled around
viral genomes and
reverse transcriptase
molecules.
7 Vesicles transport the
glycoproteins from the ER to
the cell’s plasma membrane.
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
What determines the damage a virus does?
One item is the type of cell it infects…
Examples:
HIV – immune system cells
Influenza – respiratory cells
Polio – neurons (can’t
divide)
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Vaccinations
1. Edward Jenner
A. Credited with
discovering the first
vaccine in 1798
B. The disease was small
pox
C. He observed that milk
maids (people that milked
cows) did not get small
pox.
D. Took the pus from these people infected with cow pox (a similar virus
to small pox that you catch from cows) and injected it into other people.
E. The cow pox pus somehow protected these people against small
pox
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Vaccinations
2. How do vaccines work?
- By injecting the cowpox pus,
the immune system mounts
an attack against the virus in
the pus.
- The immune system remembers
the foreign substances it attacks
and is prepared if it attacks
again…
- Since the small pox virus is so similar to the cow pox virus, the
immune system is prepared for the small pox virus as well...
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Vaccinations
2. How do vaccines work?
- Most modern day vaccines are
typically an injection of dead or
weakened (attenuated) viruses or
viral proteins…more about this
when we look into the immune
system in detail.
Chapter 24: The Immune System
NEW AIM: How does the body defend itself against MO’s?
I. Nonspecific vs. Specific Immunity
B. Specific immunity
(The Immune System) OVERVIEW
Memory T-cells are also made from Tcells activated by Helper T-cells. For a
future encounter with the same
antigen carrying pathogen.
Chapter 24: The Immune System
NEW AIM: How does the body defend itself against MO’s?
I. Nonspecific vs. Specific Immunity
B. Specific immunity (The Immune
System)
vii. Memory cells
a. Memory B and T-cells are reservists for next time that specific
antigen shows up:
Primary immune response
The first time the lymphocytes see the antigen.
Antibodies are made, but relatively slowly due to
the small number of B-cells activated and only a
relatively small number of antibodies are made
compared to the second time the lymphocytes
see the antigen for the same reason.
Secondary immune response
The secondary response results upon reexposure to the antigen. You have millions of
memory B-cells. Most of them will be activated
and antibodies are made quickly and in large
number thanks to the large number of cells. You
do not get sick. It must be the same antigen. Any
mutation that changes the structure of the
antigen will not elicit the secondary response.
Fig. 24.8
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Vaccinations
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Vaccinations
Chapter 18 - Genetics of Viruses and Bacteria
NEW: Viruses: Packaged Genes…
Fig 10.19
Tobacco Mosaic Virus – Plants get viruses t
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
1. Droplet Contact - coughing or sneezing on another person
Ex. Chicken pox, common cold (rhinovirus), influenze (flu),
Tuberculosis, Measles, Mumps, Rubella, Pertussis, Strep throat
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
2. Direct Physical Contact - touching an infected person,
including sexual contact
Ex. Sexually transmitted diseases, Athlete’s foot (fungal), Warts
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
3. indirect contact - usually by touching a contaminated surface
like a door knob or your desk. (ex. Rhinovirus…common cold)
4. airborne transmission - if the microorganism can remain in
the air for long periods (essentially droplet transmission)
5. fecal-oral transmission - usually from contaminated food or
water sources (cholera, hepatitis A, polio, rotavirus, salmonella)
6. vector borne transmission - carried by insects or other
animals (malaria – a protist)
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
This is why surgeons look like this…
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
…and people working in a biosafety level 4 laboratory look like th
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Bacterial and Viral Transmission
Biosafety Levels
Examples
Non-pathogenic E. coli
(Escherichia coli
Hepatitis A, B, C, influenz
Tuberculosis, West Nile Virus, Anthr
Ebola virus, small pox , Argentine
hemorrhagic fevers, Marburg virus,
Lassa fever, Crimean-Congo
hemorrhagic fever
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Viroids
1. Circular RNA molecules that infect plants (only several hundred
nucleotides
long) proteins
2.
DO NOT encode
3. The RNA molecules replicate inside plant cells using their machinary
THEY ARE JUST SINGLE MOLECULE!!
TEM of circular viroid RNA (black
Plants infected with varying
degrees of viroid particles (control
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Prions
1. Infectious Protein!!
2. Cause a number of degenerative brain diseases in various animals
Ex. scrapie in sheep, mad cow disease in cows, Creutzfeldt-Jakob disease
in humans
3. Transmitted through ingestion of food with these prions in them like eating
beef from cattle that had mad cow disease.
ALARMING CHARACTERISTICS
1. They are slow-acting
- Takes about 10 years until you see symptoms
2. Virtually Indestructable
- They are not destroyed (denatured) by heating to normal cooking
temperatures
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
Prions
How can a protein, which cannot replicate itself, be a transmissible
pathogen?
Hypothesis:
- A prion is a misfolded form of a protein normally present in brain cells
- When the prion gets into a normal cell, with the normal form of the protein,
it converts the normal protein to the prion form.
You eat prion infected beef Prion gets into neurons in your brain and turn normal
protein into prion form…chain reaction.
Chapter 18 - Genetics of Viruses and Bacteria
Transmission
BACTERIAL
GENETICS
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
How do bacteria
(prokaryotes) they take
up DNA…
(it is more than just mutation that gives
certain species of bacteria their genetic
diversity)
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Reproduce by binary
fission
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Reproduce by binary
fission
How do bacteria maintain genetic
One way is through mutation since they can
diversity?
Replication of single, circular bacterial reproduce so quickly leading to millions upon billions
chromosome preceding binary fission of slightly different individuals in only a days time.
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Reproduce by binary
fission
Is this the only way they maintain
diversity?
Replication of single, circular bacterial Absolutely not…let’s look at other ways to do this…
chromosome preceding binary fission
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Look at this experiment and explain what is being observed:
How were these bacteria able to exchange genes (DNA)?
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Three major methods have evolved by which bacteria take
up foreign DNA to enhance diversity:
1. Transformation
1. Bacteria can take up a free piece of
bacterial DNA
2. Crossing-over will occur between
exogenous DNA and the bacterial
chromosome.
Fig. 12.1A-C
Recall Griffith’s experiment
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
2. Transduction
Bacteriophage is mistakenly packaged
with bacterial DNA. Injects this DNA
into another bacteria.
Recall Hershey and Chase
Fig. 12.1A-C
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
2. Transduction
Bacteriophage is mistakenly
packaged with bacterial DNA.
Injects this DNA into another
bacteria.
Fig. 18.6
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
“Male” (F+) bacteria extend sex pili called a
mating bridge (long tube) to “female” (F-)
bacteria. Part of chromosome is replicated and
transferred.
F+
F-
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
F+ means the cell has the so-called F (fertility)
factor
What is an F factor?
It is a special segment of DNA that can be part of:
F+
F-
1. The bacterial chromosome OR
2. A plasmid
Now what’s a plasmid?
Bacteria can have small, circular extrachromasomal (not the chromosome) pieces of
DNA.
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Lysed bacterium
The majority of the DNA above that has spilled out of the bacterium is chromosomal, but
you can see smaller circular pieces not part of the chromosome…plasmids.
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Plasmid
- Small, circular piece of DNA distinct from bacterial chromosome
- has own origin of replication (ori)
- carries genes in nature or humans can modify them and insert genes
into the so-called polylinker region
- called vectors when used by humans as tools of genetic engineering…
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
F+ means the cell has the so-called F (fertility)
factor
The F plasmid
A special plasmid containing the F factor plus some
25 other genes needed for the production of sex pili
F+
F-
***This plasmid has the ability to integrate into the
chromosome of the bacterium or remain separate
(see next slide).
F+ cells have the F plasmid and can form sex pili
and exchange DNA with an F- cell.
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
The F- cell is now and F+ cell because it now has the F plasmid and can form sex pili
with other F- cells and pass along DNA.
Fig. 18.18
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
As mentioned earlier, the F plasmid has the potential to integrate into the
chromosome of the bacterium as shown above resulting in what we call an Hfr (High
frequency of recombination) cell.
Fig. 18.18
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Now when the plasmid begins to replicate, it will also replicate part of the bacterial chromosome giving
new genes to the recipient cell. Crossing over and therefore recombination will occur within the
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
There are three methods by which bacteria take up DNA in n
3. Conjugation
Complete picture
of the two
possibilities
Fig. 18.18
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
1. Transformation 2. Transduction
3. Conjugation
Where have we observed transformation before in this class?
The Griffith experiment when he mixed the R strain with
the heat-killed S strain…
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
β-lactam ring
R plasmids (aside)
1. R stands for resistance
2. These are bacterial plasmids that carry
genes that confer resistance to antibiotics like
ampicillin
ampicillin
3. The gene that confers resistance is
called AmpR (ampicillin resistance). What
protein does is code for?
It encodes the protein β-lactamase
Guess what is does:
β-lactamase with ampicillin
bound in the active site
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
1. Also known as “jumping genes”
Insertion sequence
Nobel Prize, Cold Spring Harb
5
A T C C G G T…
A C C G G A T…
3
3
TAG G C CA…
TG G C CTA…
5
Transposase gene
Inverted
Inverted
repeat
repeat
(a) Insertion sequences, the simplest transposable elements in bacteria, contain a single gene that
encodes transposase, which catalyzes movement within the genome. The inverted repeats are
backward, upside-down versions of each other; only a portion is shown. The inverted repeat
sequence varies from one type of insertion sequence to another.
Figure 18.19a
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
1. Also known as “jumping genes”
Nobel Prize, Cold Spring Harb
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
1. Also known as “jumping genes”
Transposon
Insertion
sequence
Antibiotic
resistance gene
Insertion
sequence
5
3
3
5
Inverted repeats
Transposase gene
(b) Transposons contain one or more genes in addition to the transposase gene. In the transposon
shown here, a gene for resistance to an antibiotic is located between twin insertion sequences.
The gene for antibiotic resistance is carried along as part of the transposon when the transposon
is inserted at a new site in the genome.
Figure 18.19b
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
DNA-transposons
vs
Retrotransposons
Almost 50% of the human
genome is composed of
retrotransposons
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
DNA transposon:
Chapter 12 - DNA Technology and the Human Genome
How can we use bacteria to manipulate DNA and protein?
Transposable Elements (Transposons)
DNA-transposons
Important in gene duplication
during S phase of meiosis
Chapter 11 - The Control of Gene Expression
NEW AIM: How are genes regulated (controlled) in prokaryotes?
Bacteria, like all other organisms,
respond to their environment by
regulating gene expression and
protein/enzyme activity…
(a) Regulation of enzyme
activity
Precursor
Feedback
inhibition
(b) Regulation of enzyme
production
Enzyme 1
Gene 1
Enzyme 2
Gene 2
Enzyme 3
Gene 3
Enzyme 4
Gene 4
(a) Negative Feedback: You have
already seen how the product of a biosynthesis
pathway like the amino acid tryptophan (trp) can
allosterically inhibit an enzyme in its production
pathway thereby shutting down its own
production (negative feedback).
(b) Regulating gene expression:
Regulation
of gene
expression
–
Genes can also be turned on/off.
–
Let’s look at how bacteria regulate
gene expression first in relation to
lactose and then trptophan…
Figure 18.20a, b
Enzyme 5
Tryptophan
Gene 5
Chapter 18 - Genetics of Viruses and Bacteria
Questions
1. “Jumping genes” are known as __________________
and always code for the enzyme known as
_________________.
2. An F+ cell is said to be “fertile” because it carries
with it the ________________.
3. SRP RNA is found where in the cell?
4. How many different aa-tRNA synthetases are there?
5. Amino acids are added to what end of the tRNA by aatRNA synthestase.
6. If the anticodon for a given tRNA is 3’-GCG-5’, what
letters would you look for on the genetic code chart to
determine the amino acid attached to this tRNA?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
In order to begin to understand this process, we
will look at a set of three genes involved in
Glucose
and galactose
lactose metabolism (the
hydrolysis
of lactose to
_______________) called the…
Lactose (Lac) Operon
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
LacA
Anatomy of an operon (only prokaryotes have operons)
The terminator
An operon typically contains a:
sequence
1. Promoter
2. Operator
3. A set of genes (3 in this specific case)
A. LacZ
B. LacY
C. LacA
4. What critical gene part is missing from this figure?
The terminator sequence
The regulatory gene (LacI) is found OUTSIDE of the operon.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
LacA
The three gene products (can you guess what they might be?):
1. LacZ codes for β-galactosidase
- The enzyme that hydrolyzes lactose to glucose
and galactose
2. LacY codes for permease
- A passive lactose transporter protein that sits in
the membrane and allow lactose to diffuse into the
cell.
3. LacA codes for transacetylase
- Exact function not yet known…
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
QUESTION
If lactose is present around the cell (perhaps it is one of the
bacterium in your mouth and you just drank a glass of
milk), should these genes be turned on or off?
They should be ON since lactose is present and will need to be
hydrolyzed so the glucose and galactose can be used to make ATP
of for biosynthesis.
Let’s look at how this operon works to control expression of these three
genes…
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
1. The regulatory gene codes for the repressor protein.
A. What does repress mean?
- To prevent
B. What will this protein do then?
- It will prevent the expression of the genes (turn them
Fig. 11.1B - Any guess how it might do this?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
1. The regulatory gene codes for the repressor protein.
C. It represses by binding to the Operator sequence and in
doing so blocks the promoter sequence.
Fig. 11.1B
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
1. The regulatory gene codes for the repressor protein.
C. It represses by binding to the Operator sequence.
-When it binds the operator, it will interfere with RNA
polymerase binding to the promoter. The genes are
off.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
ALL FOR ONE AND ONE FOR ALL
Notice that all three genes are turned on/off together.
Eukaryotes do not typically do this. They turn genes on/off
individually.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
Q1. How do you suppose these genes will be turned ON when lactose is
present?
A1. Somehow the repressor needs to fall off.
Q2. How can we get it to fall off? (HINT: you are changing its
function)
A2. You need to change its structure.
Q3. How can we change the structure?
A3. Bind something to it…a ligand.
Q4. What should the ligand be?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
The ligand should be lactose itself since in the presence of lactose
these genes should be turned ON.
Fig. 11.1B
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Activating the operon:
1. Lactose binds the repressor.
2. A conformational (shape) change occurs and the repressor falls off
the operator.
3. RNA polymerase now binds to the promoter and begin
transcription of all three genes in one long mRNA.
4. Ribosomes translate the mRNA into proteins.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Q1. What will happen when β-galactosidase breaks down most of the
lactose?
A1. Lactose will fall off the repressor and the repressor will once
again bind to the operator and turn the genes off.
Q2. Why not just leave these genes on all the time?
A2. This would be a huge waste of resources…ATP, amino acids,
ribosomes, nucleotides, RNA polymerases and space.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
To be more detailed about it…
A small amount of lactose is converted to allolactose by an enzyme in the cell. It is actually
allolactose that is what we call the inducer, which simply means it inactivates the
repressor (aka induces transcription).
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Lac repressor
protein
Repressor bound to
the operator
Lac operon – The
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
In reality, the presence of lactose alone is not enough to
induce the transcription of the lac gene…why would this
be logical?
Because there could be other sugars in excess
like glucose. Why waste ATP going after lactose if
you are already overloaded.
How does the bacterium sense the levels of glucose and
translate this information to the genome you ask…
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
When glucose is absent and lactose present, cAMP levels
are1.high…
cAMP is an allosteric activator of CAP (catabolite activator protein)
2. CAP will bind to the CAP-binding site on the promoter and recruit RNA
polymerase resulting in the production of much mRNA:
Promoter
DNA
lacl
lacZ
CAP-binding site
cAMP
Inactive
CAP
RNA
Operator
polymerase
can bind
Active
and transcribe
CAP
Inactive lac
repressor
(a) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized.
If glucose is scarce, the high level of cAMP activates CAP, and the lac operon produces
Figure 18.23a
large amounts of mRNA for the lactose pathway.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
When glucose is present with lactose, cAMP levels are
low…
1. CAP is inactive and RNA polymerase will not bind well to the promoter even if the
repressor is not present.
2. Little mRNA made
Promoter
DNA
lacl
lacZ
CAP-binding site
Operator
RNA
polymerase
can’t bind
Inactive
CAP
Inactive lac
repressor
(b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized.
When glucose is present, cAMP is scarce, and CAP is unable to stimulate transcription.
Figure 18.23b
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
How exactly does glucose lower the levels of cAMP?
1. Obviously the activity of adenylyl cyclase needs to be lowered, but glucose does
not interact directly with this enzyme…
Not something you should
memorize, just understand…
Figure X. Control of adenylate cyclase via the phosphotransferase system. A. IIA, IIB, IIC, and HPr comprise the
phosphotransferase system. When glucose is present, the phosphorylated forms of IIAGlc are low because glucose siphons off the
phosphate. IIAGlc then interacts with and inhibits adenylate cyclase activity. B. In the absence of glucose, the phosphorylated forms of
glucose-specific IIAGlc and IIBCGlc accumulate because they cannot pass the phosphate to substrate (there is no glucose). Adenylate
cyclase functions in this situation to produce cAMP. The inset on the right shows the conversion of ATP to cyclic AMP by adenylate
cyclase.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
- This operon contains fours genes whose
protein products are responsible for
synthesizing (making) the amino acid
tryptophan.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
When would you want to turn these genes on?
When tryptophan is NOT present, because that is when
you need to make it… when trp is present, it will bind to
and activate the repressor:
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
How does this compare to the lac operon?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
Inducible operon
You can turn ON (induce) the
operon by adding something
(lactose in this case)
Repressible operon
You can turn OFF (repress)the
operon by adding something
(Tryptophan in this case)
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
I do not recommend memorizing the difference.
Think about is logically:
1. The repressor bind to the operator
2. When it is bound the genes are off
3. You need the lactose break down genes
when lactose is present.
4. Therefore, when lactose binds to
repressor, it should fall off operator
5. Likewise, when trp is present, the trp
synthesis genes are unnecessary because
you
have it already
6. Therefore,
Trp when Trp binds to the
repressor, the repressor should bind the
operator and shut the genes off.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Trp operon in detail…
Tryptophan (Trp) is a
corepressor since it
represses along with the
repressor.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
The trp repressor
(with trp bound)
binding to the
operator sequence.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Both cases are examples of repression…
…but there can also be activation by activator
proteins as we shall see in the next slide.
Chapter 18 - Genetics of Viruses and Bacteria
Questions
1. A functioning unit of genomic DNA containing a
cluster of genes under the control of a single promoter.
2. The lac genes in E. coli are turned on when what two
conditions are present in the cell?
3. The major difference between how the trp genes are
regulated compared to how the lac genes are regulated.
4. When glucose concentrations are low within an E.
coli cell the concentration of _________ is _________
causing the activation of _____________, which is
required
RNA to
pol.
5. What isfor
Χ2recruiting
analysis used
determine?