VIRUS DEFINITION Non-Living particle that causes disease Pathogen: any agent that causes disease

Human papillomavirus: cause of sexually transmitted infections like genital wartssmallpox

HISTORY OF VIROLOGYSmallpox epidemics

Reached epidemic size before 1800 Thousands died or survivors were disfigured Survivors were thereafter immune Started inoculating with a mild form Problem: risk of dying!

HISTORY OF VIROLOGYMilkmaids and Cowpox

Milkmaids seemed immune to smallpox Milkmaids often got cowpox (harmless) Use cowpox to safely immunize

HISTORY OF VIROLOGY1796 Edward Jenner

Took matter from cowpox sore on milkmaid Injected cowpox matter into a boy Inoculated boy with smallpox

Boy remained healthy!

VIRUSES SEEM ALIVE

Contain protein and DNA or RNA Reproduce Evolve

HIV has an amazing knack for evolving

VIRUSES DON’T SEEM ALIVE!

Obligate parasites: must have host cell Cannot move: spread by wind, water, food, secretions Smaller than bacteria: 20 to 250 nanometers

100 flu viruses = length of 1 bacterium!

VIRUSES ARE NOT CELLS

NOTE: No cell membrane, nucleus or organelles!

CAPSID (protein coat)

CORE (DNA or RNA)

SPIKES (chemical recognition)

ENVELOPE (surrounds capsid)

How do viruses spread?

Virus is non-living outside the host cell Spread by air, water, food, body fluids

HOW DO VIRUSES RECOGNIZE A HOST?

Glycoproteins: spikes of carbohydrate + protein Embedded in viral envelope

HOW DO VIRUSES RECOGNIZE A HOST?

Viral glycoproteins can recognize receptor proteins on the host cell

How do viruses find a host cell?

Virus needs to recognize host cell before infection Envelope protein “fits” host receptor molecule

lock

key

envelope protein

host receptor molecule

How are viruses classified?

Not classified in any kingdom of life Classification is based on 3 characteristics

1 capsid helical, icosahedral,

spherical, head and tail, or filamentous?

2 envelope present or absent?

3 nucleic acid DNA or RNA?

What is a helical capsid? In some viruses the capsid or protein coat is a

corkscrew shape

RNA

capsid

What is an icosahedral capsid?

capsid

DNA

In some viruses, like the polio virus, the capsid or protein coat, is a geometric shape

What is a spherical capsid?

capsidRNA

In some viruses, like the influenza virus, the capsid or protein coat, is a ball shape

What is a filamentous capsid?

In some viruses, like the Marburg virus or the ebola virus, the capsid or protein coat, is a stringy shape

What is a Head and Tail capsid?

In some viruses, like a bacteriophage, the capsid or protein coat, is a stringy shape

HOW DO VIRUSES REPLICATE?The Lytic Cycle

(DNA) + TRANSLATION (CAPSIDS)

: DNA + CAPSIDS

LYSIS!

HOW DO VIRUSES REPLICATE?The Lysogenic Cycle

lysis

AIDS (Acquired Immune Deficiency Syndrome)

Caused by Human Immunodeficiency Virus (HIV) Symptoms: immune system failure Transmission

AIDS (Acquired Immune Deficiency Syndrome)

Structure and size: enveloped icosahedron, 125 nm Specificity: single host, human Perhaps 2 million Americans infected Much worse in Africa and Caribbean

HIV Replication

AIDS (Acquired Immune Deficiency Syndrome)

Prevention means lowering transmission Potential cures

Interfere with

RNA transcriptase Interfere with

translation of protein