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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 parts.
3. An 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 Adenovirus.
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-cells
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 capsid.
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
Tail
Capsid sheath
RNA
Glycoprotein
70–90 nm (diameter)
18 × 250 mm
20 nm
50 nm
(a) Tobacco mosaic virus (b) Adenoviruses
Glycoprotein
80–200 nm (diameter)
50 nm
(c) Influenza viruses
DNA
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
Tail
Capsid sheath
RNA
Glycoprotein
70–90 nm (diameter)
18 × 250 mm
20 nm
50 nm
(a) Tobacco mosaic virus (b) Adenoviruses
Glycoprotein
80–200 nm (diameter)
50 nm
(c) Influenza viruses
DNA
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
Fig. 10.17
(two 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 not available.
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 infections
- Symptoms range from those 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 vaccination.
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 HPV
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 nucleus
C. 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 envelope
H. 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
Contagious via respiratory secretions
(coughing/sneezing/sharing glass/kissing/
etc…)
Before infection
After infection
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 his hands
- In 1% 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 RNA
3. 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
Capsid
bind to specific receptor molecules
(not shown) on the host cell,
promoting viral entry into the cell.
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
Viral RNA
0.25 µm
HIV entering a cell
3 Reverse transcriptase
catalyzes the synthesis of
a second DNA strand
complementary to the first.
Reverse
transcriptase
RNA-DNA
hybrid
4 The double-stranded
DNA is incorporated
as a provirus into the
cell’s DNA.
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 too…
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 this…
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, influenza
Tuberculosis, West Nile Virus, Anthrax
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)
2. DO NOT encode proteins
3. The RNA molecules replicate inside plant cells using their machinary
THEY ARE JUST SINGLE MOLECULE!!
TEM of circular viroid RNA (black rings)
Plants infected with varying degrees of
viroid particles (control on left)
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 diversity?
Replication of single, circular bacterial
chromosome preceding binary fission
One way is through mutation since they can reproduce so
quickly leading to millions upon billions 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
chromosome preceding binary fission
Absolutely not…let’s look at other ways to do this…
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 nature.
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 nature.
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 nature.
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 extra-chromasomal
(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 nature.
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 nature.
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 nature.
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 nature.
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 nature.
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 nature.
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 nature.
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 nature.
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 recipient.
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 nature.
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 Harbor
5ʹ′
A T C C G G T…
A C C G G A T…
3ʹ′
3ʹ′
TAG G C CA…
TG G C CTA…
5ʹ′
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 Harbor
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
5ʹ′
3ʹ′
3ʹ′
5ʹ′
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: Genes can also
Regulation
of gene
expression
–
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 aa-tRNA
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 lactose metabolism (the
Glucose and galactose called the…
hydrolysis of lactose to _______________)
Lactose (Lac) Operon
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
LacI
LacZ
LacY
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
LacI
LacZ
LacY
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 off)
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 sequence
Lac operon – The video
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 are high…
1. 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 for recruiting RNA pol.
5. What is Χ2 analysis used to determine?