Transcript File - Hawk Nation Biology

VIRUSES NOTES
Prior Knowledge
• What are some viruses you are familiar with?
• How do we cure virus infections?
• Why do we have computer viruses?
CHARACTERISTICS OF VIRUSES
• Prokaryotic or Eukaryotic: Neither (no
organelles or membranes)
• Unicellular or Multicellular: Neither
(nucleic acid covered by a protein)
• Autotroph or Heterotroph: Neither (food
is not metabolized for energy)
• Which Kingdom do they belong to?
None
CHARACTERISTICS OF VIRUSES
• 2 MAIN PARTS OF A VIRUS:
1. PROTEIN COAT (CAPSID):
PROTECTS THE NUCLEIC ACID CORE
2. CORE OF NUCLEIC ACID (CAN BE
DNA OR RNA)
▫ An envelope is found in some viruses
(usually those that infect animal cells). It
is an additional protective coating.
EXAMPLE OF A BACTERIOPHAGE
PROTEIN
COAT
(CAPSID)
VIRAL DNA
SHEATH
TAIL FIBERS
Viral morphology (shapes)
(Label the diagrams)
Typical Bacteria virus
Animal virus
Typical Plant virus
Typical
Viruses are sub-cellular
• Viruses are among the smallest infectious
agents
• Most viruses cannot be seen by light
microscopy and can only be seen
by electron microscopy.
• They are very small…20 to 300 nm.
• They are so small that it would take
30,000 to 750,000 of them, side by side,
to stretch to one cm.
Proportional size of a virus to a bacteria
HOW DO VIRUSES MULTIPLY?
• Viruses perform replication in other cells called
hosts.
• The two replication cycles that viruses go
through are the lytic and the lysogenic cycles.
• The two cycles differ because in the lytic cycle a
virus immediately replicates after entering the
cell and in the lysogenic cycle the viral DNA
replicates itself in a way that doesn’t kill the host
cell immediately.
• Bacteriophage = Virus that infects bacterial cells
LYTIC CYCLE
Quick Process
Lytic cycle
LYSOGENIC CYCLE
Lysogenic Infection
Slow Process
prophage or provirus
Lysogenic infection includes the lytic
cycle as well.
Lytic vs lysogenic
• Viral infections that are lytic, destroy host cells
quickly (& move on…)
▫ Ex: Ebola, Chicken Pox
• Lysogenic infections destroy host cells slowly or
not at all. Lysogenic viruses undergo lytic cycle
when the host cell becomes stressed (may be
recurring)
▫ Ex: HIV, herpes, Shingles
HOW ARE VIRUSES CLASSIFIED?
• VIRUSES CAN BE CLASSIFIED BY:
▫ A. SHAPE
▫ B. HOST
▫ C. FUNCTION
Examples of Different Types of Human
Viruses
Influenza (Flu)
Viruses leaving cell
Examples of Different Types of Human
Viruses
Examples of Different Types of Human
Viruses
Smallpox & Hanta virus
Examples of Different Types of Human
Viruses
Marburg & Lassa
Examples of Different Types of Human
Viruses
Ebola
THREE TYPES OF HOSTS
A. PLANT
Ex. Tobacco Mosaic Virus
B. ANIMAL
Ex. Rabies, Foot & Mouth Disease
C. HUMAN
Ex. Common cold, measles, chicken pox,
mumps, HIV
TREATMENT OF VIRAL DISEASES
• Viral diseases cannot
be cured by
antibiotics.
• Generally with viral
infections you are
limited to relieving
symptoms while your
immune system
battles the virus.
HUMAN USES FOR VIRUSES
1. VACCINES
• When you inject a person with a harmless –
weakened or dead form of a virus
• This stimulates the immune system to produce
cells and proteins that will destroy that type of
virus, if it enters the body again
• This helped to end epidemics of smallpox,
polio and measles
HUMAN USES FOR VIRUSES
2. GENETIC ENGINEERING
• Viruses can help correct genetic defects by
carrying desirable genes from one cell to
another
3. AGRICULTURE
• Help control pests that destroy human food
crops
• They eliminate harmful insects without
creating pollution
Viroids and Prions
• Viroids have genetic material but no protein
coat.
• Prions are made of protein but have no nucleic
acid.
• Like viruses, viroids and prions are not made of
cells but can cause disease.
Viroids
• Disease causing genetic material
• Smallest known agents of infectious disease.
• Made up of nucleic acid but uniquely
characterized by the absence of a capsid.
Prions
• Disease causing proteins
• A prion is a disease-causing agent
• Unlike viruses they appear to lack nucleic acid
(DNA or RNA).
Mad-Cow Prion
Diseased brain tissue caused by
Mad-Cow Prion
Infection
• All viruses, viroids,
and prions have a
parasitic
relationship with
the host cell.
• They require a
host cell to
replicate.
Check for Understanding
• What are the differences between viruses,
viroids, and prions?
Think about it……
•Is a
virus
alive?
Viruses
• Hard to classify as living, because:
• Contain only a protein coat (capsid) and
a nucleic acid core (DNA or RNA)
▫ May also contain a protein
envelope that protects virus from host
organism recognition
• They don’t reproduce themselves… the
virus is reproduced by the host cell