Transcript VIRUSES Honors Biology

VIRUSES
NONLIVING
PARTICLES
Viruses
 Smaller than bacteria
 Known since late 1800’s but no way
to study them
 1935 Tobacco mosaic virus was
crystallized
 1st time scientists suspected virus
chemical and not living
WHAT IS A VIRUS?
PARTICLES OF NUCLEIC
ACIDS, PROTEINS AND IN
SOME CASES LIPIDS
THAT CAN REPRODUCE
ONLY BY INFECTING
LIVING CELLS.
Virus Structure (bacteriophage)
Helical Virus Structure
Icosahedral Virus Structure(polio)
HOW VIRUSES WORK
ONCE INSIDE OF LIVING
CELLS, VIRUSES USE THE
MACHINERY (NUCLEIC
ACIDS) OF THE INFECTED
CELL TO PRODUCE MORE
VIRUSES.
TYPICAL VIRUS STRUCTURE
MADE OF A CORE OF
EITHER DNA OR RNA
SURROUNDED BY THE
CAPSID - A PROTEIN
COAT
Envelope
 Membrane-like structure outside of
the capsid;
 Made mostly of lipids;
 Taken from a host cell membrane
during replication;
 Allows new viruses to infect host cells
during 1st stage of viral infection;
Envelope
 Glycoproteins – projections of
protein-containing sugar chains that a
virus uses to attach to a host cell.
Viruses that have an envelope




Influenza
Chickenpox
Herpes simplex
HIV
THE SHAPES OF VIRUSES
VIRUSES ARE SPECIFIC
VIRUSES BIND PRECISELY
TO PROTEINS ON THE CELL
SURFACE
THE CAPSID INCLUDES
PROTEINS THAT TRICK THE
CELL INTO ALLOWING IT
INSIDE
GROUPING VIRUSES
 BASED ON PRESENCE OF CAPSID &
ENVELOPE, IF THEY CONTAIN RNA
OR DNA AND IF NUCLEIC ACID IS
SINGLE OR DOUBLE-STRANDED;
 TABLE 25-2, PAGE 489, LISTS
COMMON VIRUSES OF HUMANS AND
THEY ARE GROUPED;
VOCABULARY FOR
UNDERSTANDING
 BACTERIOPHAGE – VIRUSES THAT
INFECT BACTERIA;
 PROPHAGE – INTRACELLULAR
B.PHAGE THAT IS HARMLESS TO THE
HOST CELL;
VIRAL INFECTION
LYTIC INFECTION – A
VIRUS INVADES A HOST
CELL, PRODUCES NEW
VIRUSES, DESTROYS THE
HOST CELL & RELEASES
THE VIRUSES
LYTIC INFECTION
 LYTIC VIRUSES ARE VIRULENT –
DEGREE OF PATHOGENICITY OF A
MICROBE;
 VIRULENT (L) – “FULL OF POISON”
 INFLUENZA; POLIO
 A SINGLE VIRUS CAN INFECT A CELL
AND PRODUCE 100 VIRUS PARTICLES
IN 20 MINUTES
LYTIC CYCLE STAGES
 BACTERIOPHAGE ATTACHES TO CELL
AT A RECEPTOR SITE;
 B. PHAGE RELEASES AN ENZYME
THAT WEAKENS A SPOT IN CELL
WALL OF HOST;
 B. PHAGE INJECTS DNA INTO THE
HOST CELL;
 VIRUS TAKES CONTROL OF HOST’S
DNA;
LYTIC CYCLE
 VIRUS TRANSCRIBES MESSENGER
RNA FROM THE VIRUS’ DNA;
 THE M. RNA IS TRANSLATED INTO
PROTEINS THAT FORM B. PHAGE
CAPSIDS CONTAINING THE VIRUS
 AN ENZYME CAUSES THE HOST CELL
TO LYSE (BURST) RELEASING THE
NEW BACTERIOPHAGES.
VIRAL INFECTION
LYSOGENIC CYCLE:
 TEMPERATE VIRUSES – DON’T KILL
HOST IMMEDIATELY;
 BACTERIOPHAGE;
 PROPHAGE;
 HIV A LYSOGENIC VIRUS;
LYSOGENIC CYCLE
 B. PHAGES ATTACH TO A RECEPTOR
SITE, RELEASE AN ENZYME THAT
WEAKENS CELL WALL OF HOST AND
INJECTS DNA.
 DNA INTEGRATES ITSELF INTO THE
HOST CELL’S DNA
LYSOGENIC CYCLE
 B. PHAGE DOES NOT IMMEDIATELY
CREATE NEW RNA AND VIRAL
PROTEINS;
 B. PHAGE DNA MOLECULE
INTEGRATES ITSELF INTO A
SPECIFIC SITE OF THE HOST CELL’S
GENOME – THE PROPHAGE.
LYSOGENIC CYCLE
 PROPHAGE REPLICATES WHENEVER
THE HOST BACTERIUM
REPRODUCES;
 EACH BACTERIAL OFFSPRING IS
INFECTED WITH A PROPHAGE;
 AT SOME POINT, PROPHAGE
BECOMES VIRULENT, ENTERS LYTIC
CYCLE, MAKING M. RNA &
DESTROYING HOST CELL.
VIRUS PREVENTION
VACCINE-PREPARATION OF
A WEAKENED OR KILLED
VIRUS OR VIRAL PROTEINS
THAT STIMULATES THE
IMMUNE SYSTEM
PRODUCING IMMUNITY
AGAINST THE VIRAL
DISEASE.
Types of Virus Vaccines
 Inactivated viruses – do not replicate
in a host system;
 Attenuated viruses – genetically
altered so they are incapable of
causing disease under normal
circumstances;
 Protection is greater and lasts longer
with vaccine from attenuated viruses;
Prevention/Treatment
 Antiviral drugs – interfere with viral
nucleic acid synthesis;
 Very few antiviral drugs exist;
 Acyclovir – herpes simplex
 Azidothymidine – inhibits reverse
transcriptase of retroviruses
 Protease inhibitors – interferes with
synthesis of viral capsids during viral
replication
Emerging Viruses
 Ebola – hemorrhagic virus; rapid death.
 Hantavirus – affects lungs which fill with
fluid; western U.S.
 Machupo virus – S. America; “Black
Typhus” – hemorrhagic, high fever, pain,
rapid death.
 Lassa fever virus – West Africa;
hemorrhagic virus; zoonotic – from
multimammate rat; 1-4 weeks duration
RETROVIRUSES
 VIRUSES THAT CONTAIN RNA AS
THEIR GENETIC INFORMATION –
 RNA IS USED AS A TEMPLATE TO
MAKE DNA.
 AIDS IS A RETROVIRUS
PRIONS
 PROTEIN INFECTIOUS PARTICLES
 ABNORMAL FORMS OF PROTEIN
THAT CLUMP TOGETHER IN A CELL
 EVENTUALLY KILLS THE CELL
 CONTAIN NO DNA OR RNA, ONLY
PROTEIN;
Prions may cause
 Mad cow disease (bovine spongioform
encephalopathy)
 CruetzFeld-Jakob disease
 Scrapies (sheep)