Download 18.2 Viruses and Prions

Virus and Prion Notes
Ch. 18
Chapter 18
Bacteria and Viruses
18.2 Viruses and Prions
Viruses
 A nonliving strand of genetic
material within a protein coat
 No organelles to take in
nutrients or use energy
 Cannot make proteins
 Cannot replicate on their own
Viruses – tiny non-cellular particles of genetic material
and protein. Controversy over whether living or nonliving.
Table: Reasons for classifying non-living vs. living
Non-Living
Living
No cell respiration
Reproduces within host cell
No growth or protein
synthesis
No independent
movement
No basic cell
parts/organelles
Has genetic material
No independent
functions
Larger viruses may infect smaller
viruses
Large numbers found in marine
environment which is thought to be
source of early single celled organisms.
Figure 19-11 Viruses and Cells
Section 19-2
Invasion Methods
• Flu Attack! How A Virus Invades Your
Body : NPR
Bacteriophage Invasion
• Bacteriophage invades a bacterium
Structure
• Contain a nucleic acid and
protein
• HEAD region
– Capsid--protein coat with
nucleic acid core
• TAIL region
– to attach to host
Chapter 18
Bacteria and Viruses
18.2 Viruses and Prions
Viral Infection
 In order to replicate, a virus must enter a host
cell.
 The virus attaches to the host cell using specific
receptor site on the plasma membrane.
 3D shape of the virus coat interlocks with the
matching site on the host cell (lock and key)
 Many viruses cannot be transmitted between
different species.
•Named for:
•Disease they cause
•Organs they infect
•Code Numbers differentiating
organs they infect
•Bacteriophage – means “bacteria
eater” - viruses which attack bacteria
Figure 19-9 Virus Structures
Section 19-2
Tobacco Mosaic
Virus
T4 Bacteriophage
Head
DNA
Influenza
Virus
RNA
Capsid
proteins
Capsid
RNA
Tail
sheath
Tail
fiber
Surface
proteins
Membrane
envelope
Chapter 18
Bacteria and Viruses
Viral Replication in Prokaryotes occurs in cytoplasm
as DNA is not in a nucleus – pgs. 528 – 529
Lytic Cycle
 The host cell makes many copies of the viral
RNA or DNA.
 Lysis of host cell
Lysogenic Cycle
 Viral DNA inserts, or integrates into a
chromosome in a host cell.
 Infected cell will have the viral genes
permanently.
 Viral DNA can separate and enter lytic cycle
Animated Lytic Cycle
Animated Lysogenic Cycle
Chapter 18
Bacteria and Viruses
18.2 Viruses and Prions
Bacteriophage
 A virus that infects bacteria
Other Viruses
 HIV/AIDS- spread through sexual contact
 Rabies- effects nervous system
 HPV- cancer causing virus
Figure 19-10 Lytic and Lysogenic Infections
Chapter 18
Bacteria and Viruses
18.2 Viruses and Prions
Hepatitis – DNA Virus
Herpes Virus – DNA Virus
Rhinovirus – RNA virus
Polio Virus – RNA Virus
SARS Virus – RNA Virus
Viral Replication in Eukaryotes occurs
in nucleus of cell (not pictured in text)
• 1. DNA viral diseases (not listed in text as
such) –examples: hepatitis, chicken pox,
herpes, shingles
– Structure: DNA inside protein coat virus
– Reproduction – information follows normal
pathway: DNA to RNA to proteins in cell
2. RNA viral diseases p. 526 – cold, mumps, measles,
polio, flu, AIDS, SARS, West Nile, most plant viruses
a. Structure – RNA wrapped in protein coat,
surrounded by an envelope of glycoprotein spikes that
bind with the membrane receptor proteins on the host
cell
b. Reproduction
1. protein surrounding RNA dissolves
2. RNA synthesis occurs – strand produces either
new viral RNA or protein for the viral coat and
spikes
3. New virus assembles – uses the cell membrane
to make an envelope
Damage from virus – depends upon
– Are cells lysed? (remember what lysis is?)
– What type of cell is damaged – polio damages nerves
which cannot regenerate
Plant Viruses – most are RNA viruses
– virus must breach cuticle and cell wall so damaged
plants are more susceptible
– typically rod shaped
– spreads through cytoplasmic connections between
plant cell walls
– insects and gardening tools can spread to other plants
• Emerging Viruses – how do they come into being?
– Current Hypothesis for Development of First Viruses– first
viruses were fragments of cellular nucleic acid that could
transfer to another cell. Protein coat later developed for
protection/recognition. Viral genetic material is similar to
cellular genetic material.
– Contributing Factors for current new virus development –
• RNA viruses – high mutation rate – RNA replication isn’t proofread
so more mistakes. Mutated forms do not trigger previous
immunity
• Existing viruses may spread to new host – through mutation or
new opportunity to infect a new host – Ex: Hanta Virus – to
humans from the bites, urine or droppings of infected mice or rats
• Existing virus in small populated area becomes widespread as new
methods of transmission occur – Ex: HIV
• Retrovirus – has two copies of RNA instead of
one and contains the enzyme reverse
transcriptase – Ex: HIV pg. 530
– Reverse transcriptase synthesizes DNA from RNA.
Complementary DNA strands are formed
– The double strand of DNA is then inserted into host
DNA to form a provirus which is the animal version of
a prophage
– Lysogenic-type cycle runs
– Occasionally provirus is transcribed into RNA, makes
new viruses which infects other cells
Retrovirus
The HIV virus
HIV – Retrovirus Life Cycle
• Life Cycle of HIV, a Retrovirus
Prions – proteinaceous infectious
particle (protein that can cause a
disease)
1. Normally exist in cells – not sure of function
2. Shape – multi-folded piece of paper
3. Diseases – these diseases belong to a group of diseases called
TSEs or transmissible spongiform encephalopathy – prions able
to trigger abnormal folding of certain normal cellular proteins
called prion proteins that are found in abundance in the brain
a. Mad Cow Disease
b. variant CJD – variant Creutzfeldt-Jacob disease in
humans
c. Scrapie in sheep – affects their central nervous
system, usually fatal
d. chronic wasting disease in deer and elk
Prions
Protein particles
4. Prion Infection –
a. Causes normal proteins to mutate - in brain cells,
causes lysis of cells
b. Spread when prions move to new material – not
sure how this happens but may occur when:
1. Prion exists in brain or spinal cord of a cow.
2. When the cow is butchered, contamination of
the beef occurs from nervous tissue.
3. Humans eat the contaminated beef
4. The prion enters the human’s nervous system.