VIRUS

1
Virus Notes
Ch. 18 Sec. 1,2,3
2
IMPORTANT TERMS

1. HOST

AN ORGANISM THAT SHELTERS AND NOURISHES SOMETHING.
2. RETROVIRUS -
A VIRUS THAT REPLICATES BY FIRST TRANSCRIBING RNA
INTO DNA. (HIV)
3
3. Vaccine
A substance produced from killed or weakened
pathogens
4. VIROID -
A SINGLE STRAND OF VIRAL RNA. (PLANT DISEASES)
5. PRION -
VIRAL PROTEIN MOLECULE. CAUSES DISEASES IN
ANIMALS. (MAD COW DISEASE/Creuzfeldt-Jakob).
4
6. CAPSID -
THE PROTEIN COAT OF A VIRUS.
7. PROPHAGE/PROVIRUS -
A VIRAL DNA SEGMENT INSERTED INTO A BACTERIAL CELL
8. LYSIS -
THE BREAKING APART OF THE CELL TO RELEASE NEW
VIRUSES.

• BACTERIOPHAGE-
• A VIRUS THAT ATTACKS A BACTERIA.

Read Ch. 18, Sec. 1,2,3 pages 526-538
5
CHARACTERISTICS OF VIRUSES
VIRUS (POISON) DISCOVERED BY STANLEY 1935
- TMV (Tobacco Mosaic Virus)

• Viruses are pathogensagents which cause disease

6

• Debate on living vs. nonliving
• Not normally classified (not in a Domain,
  Kingdom, etc no genus species name)
• Considered NONLIVING because they
• can only reproduce inside of living cells
• do not have a metabolism
• do not maintain homeostasis
• do not grow
• Viruses are similar to living cells in that they
• Have genetic material (DNA or RNA)
• Have proteins
• Have receptor/marker molecules on the outside for
  communication/recognition
• Change over time (mutate/evolve)

7
(No Transcript)
8
Viral Structure
9
STRUCTURE OF A VIRUS

• 2 Parts
• CORE OF NUCLEIC ACID --NUCLEIC ACID IS EITHER
  DNA OR RNA
• PROTEIN COAT
• --PROTEIN COAT is called the CAPSID

10
FIVE BASIC SHAPES OF VIRUSES

• helical
• spherical
• polyhedral
• binal/bacteriophage
• filovirus

11
(No Transcript)
12
HELICAL

• RNA or DNA coiled in a long, narrow capsid
• Ex) tobacco mosaic virus (TMV)

13
SPHERICAL

• Typically studded with receptors, may be
  enveloped (envelope around capsid)
• Ex) Influenza (flu) virus HIV

14
POLYHEDRAL VIRUS

• Geometric appearance
• Ex) adenovirus (causes the common cold)

15
BINAL

• Polyhedral capsid containing DNA or RNA
• Helical tail
• Ex) Bacteriophage (ONLY infect bacteria)

http//www.cellsalive.com/phage.htm
16
FILOVIRUS

• filovirus Filoviridae Photo Album
• Ex. Ebola
• Deadly viruses many are emergent viruses
  viruses that humans have suddenly contracted in
  isolated geographic areas
• Ex) Hantavirus and West Nile virus are emergent
  viruses (however they are NOT filo shape)

• No distinct or uniform shape
• Threadlike loops

17
Surface Marker/Receptor Proteins

• Virus surface proteins attach to cell surface
  proteins much like pieces of a puzzle fit
  together.
• This facilitates their entry across the cell
  membrane.

influenza
cell
http//www.virology.ws/2009/05/04/influenza-virus-
attachment-to-cells/
18
Viral Diseases (p. 440) Cold Influenza
(flu) AIDS Small pox (variola)vaccine by
Jenner Measles Chicken pox (varicella)
Mumps Poliovaccine by Salk Mononucleosis
Ebola Hepatitis (ABC) Yellow
fever SARS Rabies Rotavirus Rubella
(German measles) Routinely immunized against NO
Viral diseases are treatable with ANTIBIOTICS!!!
19
WARTS - are caused by viruses!
20
Viral Replication

• Viruses replicate inside living cells
• They enter a cell by injecting their genetic
  material into the cell
• tears in the plant cell wall
• binds to molecules on the cell surface and
  triggers endocytosis.

21
RETROVIRUS

• Viruses that get their genetic material copied
  backwards
• From RNA to DNA
• Ex) HIV (or human immunodeficiency virus) causes
  disease AIDS
• contain RNA inject it into the host cell
• When the virus infects the cell, they produce a
  DNA copy of their RNA
• Responsible for some types of cancer in animals

22
2 cycles for Viral Reproduction

• 1. Lytic Cycle
• 2. Lysogenic Cycle

23
Lytic Cycle

• Characterized by viral infection, replication,
  and cell destruction
• Virus enters cell, often just the genetic
  material is injected.
• Replicates viral genes by making new protein
  coats or capsids by gene expression and new
  nucleic acids (DNA or RNA) by replication.
• Soon the cell is full of new viruses that burst
  from the cell spreading the disease

24
(No Transcript)
25
LYTIC CYCLE
http//biology.about.com/library/blvirusanim.htm

1. VIRUS ATTACHES TO HOST
2. VIRUS ENTERS CELL (NUCLEIC ACID IS INJECTED)
3. REPLICATES IMMEDIATELY
4. PRODUCES MANY NEW VIRUSES
5. VIRUSES BURST FROM CELL TO INVADE OTHER CELLS
   (This is the step that harms or kills the cell)

26
Lysogenic Cycle

• the viral genome replicates without destroying
  the host cell
• virus inserts its DNA into its host DNA and it
  hides there
• Becomes a provirus/prophage
• Divides/replicates with the help of the host
  cell
• ALL WITHOUT HARMING THE CELL
• Later it will begin the lytic cycle to spread the
  virus

27
(No Transcript)
28
LYSOGENIC CYCLE

1. VIRUS INVADES CELL
2. DOES NOT IMMEDIATELY KILL HOST CELL
3. BECOMES PART OF HOSTS DNA
4. HOST CELL REPRODUCES AS USUAL (MAKING MORE VIRAL
   DNA WITHOUT KNOWING IT)
5. EVENTUALLY GOES INTO LYTIC CYCLE TO SPREAD THE
   VIRUS

http//student.ccbcmd.edu/courses/bio141/lecguide/
unit3/viruses/lysosum.html
29
VIRAL REPLICATION CYCLES
30
(No Transcript)
31
HUMAN IMMUNODEFICIENCY VIRUSa retrovirus

• HIV, the virus that can result in the disease
  AIDS, can hide for years in the nucleus of
  T-cells (white blood cells that help fight
  infection) in the Lysogenic cycle. People can
  have no symptoms, yet be spreading the disease to
  many partners.

32
HIV then begins the Lytic cycle and T-cells begin
to die. HIV infection leads to the destruction
of the bodys T cells and weakens the immune
system. This can lead to AIDS (when T cell count
is below 200 cells/ml). The patient eventually
dies from another disease (opportunistic
infection) that the immune system cant control
because there are not enough T-cells to help
fight infection.
33
Structure of HIV

• Exterior Viral envelope studded with
  glycoproteins
• Lipid bilayer made from host cell membrane
• Inside is capsid
• Inside 2 molecules of RNA

34
Viruses and Cancer Many cancers can result from
viral infections HOW? Because when a virus
infects a cell it can cause genes in the cell to
turn on or off. This can interrupt the cell
cycle, causing the cell to divide uncontrollably.
This is cancer! Ex) HPV this virus can infect
women and result in cervical cancer theres a
vaccine on the market now Ex) hepatitis can
often lead to liver cancer Ex) Epstein-Barr virus
can lead to some lymphomas
35
Wrap Up Viruses (as well as viroids and prions)
are disease-causing organisms that are not
considered to be alive according to current cell
theory for several reasons __________________
The diseases caused by viruses CANNOT be treated
with antibiotics, but many have vaccines given
via a vaccination.__
Viruses have 2 basic components__________________
Viruses have 5 basic shapes_______________________
__
Viruses replicate/reproduce inside host cells
retroviruses have an unusual method of
replication RNA to DNA. Viruses that infect
bacteria (bacteriophages) have 2 basic life
cycles ___________________ AIDS and cancer, as
well as many common infections (colds,
influenza), are caused by viruses http//www.npr.o
rg/templates/story/story.php?storyId114075029sc
emaf