Chapter_14_Viruses materi virologi.ppt.pdf

virologi

1. CHAPTER 14 VIRUSES
(PROKARYOTES)

2. Viruses
Viruses are the smallest living organisms.
A virus consists of a protein coat or capsid,
nucleic acid (RNA or DNA) and on occasion a
bit of the host’s cell or plasma membrane.
Some have an outer envelope (made of lipids
and proteins) and enzymes.
Viruses are considered noncellular, infectious
particles that must have a host to reproduce.

3. Viruses
Viral genes direct the host cell to produce
new viral particles.
Viruses can also mutate. Why is that a
problem?

4. VirusesViruses
See Fig. 13.8
Bacteriophage
(infects
bacteria).
Tobacco mosaic
virus
infects tobacco
and related
plants.
An adenovirus (20-
sided) infects
animals.
A herpesvirus
infects animals;
the envelop
comes from the
host.

5. Viral Replication – Lytic Cycle
The virus binds to specific protein receptors
on the appropriate host.
The viral genome enters the host cell.

6. Viral Replication – Lytic Cycle
The viral genes directs the host cell to
replicate its DNA or RNA.
The cell membrane ruptures (lysis) and
releases the new viral particles.

7. Viral Replication –Lysogenic Cycle
Begins the same as the lytic cycle with the
injection of the viral RNA or DNA into the
host cell.
However, it remains hidden inside the host
cell (e.g., bacteriophage).
When the bacterial cell reproduces, it
contains a bit of its nucleic acid AND the
virus nucleic acid.

8. Viral Replication –Lysogenic Cycle
The bacterial cells continue to make copies.
It becomes a problem when the virus is
triggered to move into the lytic cycle.
Why? All of those cells will begin replicating
the viral DNA or RNA.
What triggers the switch? Perhaps a lack of
food or a chemical toxin.

9. https://www.youtube.com/watch?v=8FqlTs
lU22s
(6:48)
Amoeba Sisters

10. Types of Viruses
Bacteriophages or phages infect only
bacteria, and they are species specific.
They live everywhere (e.g., soil, in our bodies,
and in food we ingest)and are harmless to
plants and animals.
These may benefit humans. Why?
Bacteriophages are harmful to bacteria.
We have some bacteriophages in our mucus
membranes (e.g., trachea) and our intestines.

11. Types of viruses
Plant viruses are usually nonenveloped.
They generally have a helical structure, and
their genome is often single-stranded RNA.
Plants have a thick cell wall (and an outer
cuticle) so the viruses cannot enter without
some kind of a wound present. They often
use disease vectors (e.g., aphids).
New plants have been developed with virus
resistance.

12. Aphids on
a butterfly
weed
R. Whitekiller

13. Plant Virus Examples
Cucumber mosaic virus
Plum pox virus
Potato virus X
Cauliflower mosaic virus
Tomato yellow leaf curl
Tobacco mosaic
African cassava woody shrub (tropical)
manioc

14. Viruses and Humans
Viruses are considered pathogenic when
they cause human diseases.
Some rhinoviruses (“nose”) affect
membranes of our respiratory system and
cause the common cold.

15. news-medical.net

16. Viruses and Humans
Some viral diseases are more persistent
than the common cold.
The herpes viruses cause cold sores, genital
herpes, mononucleosis and the chicken pox.
The initial infection causes symptoms for a
short period; however, the viruses remains
in our bodies in a latent (“resting” or
dormant) state.

17. Viruses and Humans
For example, herpes simplex virus 1 (HSV-1)
can remain latent in nerve cells. When
activated, it replicates producing cold sores
on the lips. Spreads via oral contact.
Another type of herpesvirus (HSV-2) causes
genital herpes (an STI).
cdc.gov

18. Viruses and Humans
Some viruses can cause cancer. For
example, some strains of human
papillomavirus (HPV) cause genital warts
but can also cause cancer of the cervix,
penis, mouth or anus.
Most common STI.
There is a vaccine.

19. medicalnewstoday.com
novosanis.com

20. Viruses and Hum ans
Acquired Immune Deficiency Syndrome)
(AIDS) is caused by Human
Immunodeficiency Virus (HIV-1; RNA virus)
This RNA virus replicates inside our white
blood cells.
New HIV-infected cells are produced when
the infected white blood cell replicates.
This virus makes the host vulnerable to
other infections as the number of white
blood cells is reduced.

21. Viruses and Humans
Today, more than 20 million people
worldwide have died from AIDS.
Thirty-eight million are currently infected
with HIV.
Antiviral medications lower the number of
HIV particles, but there is no cure.

23. Viruses and Humans
Ebola is an enveloped virus. Like HIV, it
originated in Africa. This virus infects fruit
bats, primates and humans.
It attacks the white blood cells and then
quickly spreads to all other cells.
Symptoms include flu-like symptoms, a
rash, vomiting, diarrhea and bleeding from
body openings (e.g., mouth and eyes).

24. Viruses and Humans
It is transmitted between humans via
bodily fluids, objects contaminated with
the virus and infected animals.
There is no vaccine and few experimental
drugs available.
cdc.com

25. Viruses and Humans
Influenza viruses (flus) are also caused by an
enveloped virus.
To attempt to keep up with ongoing
mutations, scientists create flu vaccinations.
The vaccines are designed to protect against
certain strains; however, scientists have to
predict which are most likely to pose a threat.

26. Viruses and Humans
New influenza strains arise via mutation and
viral reassortment.
Viral reassortment – swapping of genes
between related viruses that infect a host at
the same time.

27. Epidemic vs Pandemic
Epidemic outbreaks occur within a localized
area.
Pandemic outbreaks occur worldwide.
The key is prevention through sanitary
cleansing practices and vaccinations.

28. Coronoviruses – Family of Viruses
The coronavirus we are currently dealing with
is SARS-CoV-2 or Severe Acute Respiratory
Syndrome Coronavirus 2. It is an RNA virus.
This virus was first detected in Wuhan China
in March, 2020; however, the virus was
present in Wuhan’s population in December
2019. [Nature 591, 188-189 (2021).]

29. SARS-CoV-2
As of 11-1-2023, more than 1,150,119
have died from COVID 19 in the U.S. alone
(CDC data).