Transcript Chapter 18, Section 2

Chapter 18, Section 2
Viruses
Virus
• Non-living strand of genetic material with a
protein coat
• No organelles
• Do not move
• Cannot replicate on their own
• Size: 5 – 300 nm (nanometers – about 1
billionth of a meter)
Viral Diseases
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AIDS
Herpes
Measles, Mumps, Chicken Pox
Cold, Influenza
Warts, Shingles
Gastroenteritis
Polio, viral meningitis, rabies
Small Pox, Hepatitis
Where did viruses come from?
• Possibly parts of cells
– Genetic material of viruses is similar to that of
cells
Virus Structure
• Covered by an outer layer of proteins
called a capsid
• Inside the capsid – genetic material –
could be DNA or RNA
Viral Infections
• To replicate, viruses must infect host cells
– Two types of infections
• Lysogenic
• Lytic
Lysogenic Cycle
• Viral DNA enters nucleus of host cell
• DNA stays dormant
• Under the right conditions, the viral DNA is
activated and the Lytic Cycle begins
Lytic Cycle
• Host cell makes copies of viral DNA or
RNA
• Invading genetic material instructs the host
cell to make more viral protein capsids and
enzymes needed for viral replication
• New viruses start to form
• Host cell explodes and releases the new
viruses
http://www.geocities.com/madokagm/BIOL1551/lecture_notes_Nov_22_files/image002.jpg
Virus Rejects
• Retrovirus
– Has RNA instead of DNA
– Ex HIV Virus
• Prions
– Proteins that can cause infectious diseases
– Prions exist in cells, but mutations cause the
prions to be incorrectly folded – can cause
normal proteins to mutate
– Mad Cow Disease, Creutzfeldt-Jakob Disease
How much do you know?
• Which cycle causes the host cell to burst?
• What is the difference between a virus and
a retrovirus?
• What type of virus is HIV?
• Do prions have genetic material?
• Are viruses living? Give one reason why
or why not?
• Are viruses bigger or smaller than normal
cells?