Bio 220: Lecture 19 - Viruses

Front 1

define: virus

Back 1

• the word virus comes from the word that means poison
• Viruses were observed as filterable, and would pass through the clay or porcelain filters used in the past.
• Since the filtrate that came through these filters was clear, the early thinking was that this was a chemical poison

Front 2

Who is the Russian bacteriologist that injected healthy tobacco plants with filtered fluid?

Back 2

Dimitri Iwanoski in 1892

Front 3

Who is Dimitri Iwanoski?

Back 3

A Russian bacteriologist that injected healthy tobacco plants with filtered fluid. These plants soon showed signs of tobacco mosaic disease.

Front 4

What was the first human disease associated with a filterable agent?

Back 4

Yellow fever

Front 5

Filterable "poisons" are now known to be ___?

Back 5

particulate infectious agents
• we refer to them as particles since they are not alive and therefore not cells

Front 6

When were these particles first observed?

Back 6

1940's using electron microscopy

Front 7

True/False: Viruses are obligate intracellular particles that can attack all forms of life.

Back 7

true

Front 8

We refer to a virus as a ___ when it is a complete and infectious particle.

Back 8

virion

Front 9

What are the two states that viruses alternate between?

Back 9

intracellular state and an extracellular site

Front 10

When intracellular they are capable of ...

Back 10

replication, a process which involves making copies of their nucleic acids, protein coats (capsid), additional components and then assembling the parts into a complete virus

Front 11

When they are extracellular, viruses are ...

Back 11

metabolically inert (inactive or quiet).

Front 12

Viral Structure
Nucleic acids

Back 12

• viral genes are either made up of DNA or RNA
• Some viruses have as little as 1% nucleic acid content relative to their protein content, while others have as much as 50% nucleic acid content relative to their protein content.

Front 13

Most bacteriophages posses _____ as their nucleic acid

Back 13

double stranded DNA

Front 14

Most plant viruses are ___ containing viruses.

Back 14

RNA

Front 15

With respect to animal viruses, ...

Back 15

some possess DNA as their nucleic acid, while others possess RNA as their nucleic acid.

Front 16

Herpes simplex type 1 virus is an example of a ___.

Back 16

DNA virus that is double stranded.

Front 17

The polio virus is an example of ___.

Back 17

a single stranded RNA virus.

Front 18

A group known as ___ possess double stranded DNA as their nucleic acid.

Back 18

poxviruses
These pox viruses which include the smallpox virus and the cowpox virus have as many as 400 genes.

Front 19

The ___ has only 7 genes.

Back 19

adenosatellite (also called adeno-associated virus (AAV)
• single stranded DNA that is so small that it can't code for everything that it needs.
• For AAV to replicate it most co-onfect a host cell with another virus known as the adenovirus (double stranded DNA virus which is 3x as large)

Front 20

Viral Structure
Capsid (protein coat)

Back 20

the capsid coves and protects the nucleic acid. This protein coat of a virus is made up of subunits called capsomeres

Front 21

Viral Structure
Envelope

Back 21

some viruses possess a layer outside of the capsid called an envelope. The envelope consists of a combination of lipids, carbohydrates and proteins. If a virus leaves a host cell after replication by the process of extrusion (rather than by lysis), the envelope may be made up largely of the host cell plasma membrane.
• The envelope may help the virus when it comes to surviving host defenses. The host immune system may not recognize the virus as foreign when it is surrounded by a structure that is at least in part made up of the host cell membrane.
• Additional protein components of the envelope are determined by the viral genes
• Non-enveloped viruses are called "naked"
• Some viruses pick up their envelope from the nuclear membrane.

Front 22

Some viruses pick up their envelope from the _____.

Back 22

nuclear membrane

Front 23

Non-enveloped viruses are called ___.

Back 23

naked

Front 24

Viral Structure
Spikes

Back 24

some viral envelopes are covered with spikes.
• These are carbohydrate-protein complexes that project from the surface of the envelope.

Front 25

What single stranded RNA virus contains these spikes?

Back 25

influenza virus

Front 26

What are the spikes used for?

Back 26

to categorize and identify the "flu" virus

Front 27

What are HA spikes?

Back 27

• hemagglutinin spikes
• these spikes will bind to erythrocytes and form cross bridges, resulting in agglutination
• HA spikes are commonly targeted by antibodies that attack the influenza virus
• these spikes are commonly targeted by antibodies that attack the influenza virus

Front 28

What are NA spikes?

Back 28

• neuraminidase spikes
• they help the virus separate and exit from the host cell following replication
• they are used in viral identification

Front 29

How many different subtypes of HA are there?

Back 29

16

Front 30

How many different subtypes of NA are there?

Back 30

9

Front 31

The Spanish influenza of 1918 was type ___.

Back 31

H1N1

Front 32

The 2009 pandemic was a new strain of ___.

Back 32

H1N1

Front 33

What is another term for the bird (avian) "flu"?

Back 33

H5N1 - it has been problematic in the recent years

Front 34

VIRAL STRUCTURE
Viral enzymes

Back 34

viral enzymes are limited
• the viral enzymes that are present are mostly involved with the entrance and exit to and from the host cell
• Viral enzymes are typically not involved with such activities as energy production
• The enzyme lysozyme is found on the tail structures of the T-even bacteriophage.
• This enzyme breaks down the cell wall of the host bacterial cell to facilitate viral penetration

Front 35

Viral size

Back 35

using EM, viral size varies.
• The viruses range in length from approximately 20 to 1000 nm
• The smallest of viral particles is considerably smaller than bacteria.
• The largest may be close in size to the smallest bacteria (mycoplasma, rickettsias and chlamydias)

Front 36

What are the three morphologies that are based on capsid architecture?

Back 36

helical, polyhedral and complex

Front 37

define: helical

Back 37

capsid winds around in a helical spiral structure.
• The nucleic acid is found within this hollow and cylindrical capsid structure.
• Examples include the tobacco mosaic virus which is a helical single stranded RNA virus and the influenza virus which is an enveloped helical single stranded RNA virus

Front 38

define: polyhedral

Back 38

• this geometrically formed capsid looks like a soccer ball
• The polyhedral viruses contain many sides and most are 20 sided and are called isohedrons
• The isohedron viruses contain 20 triangular sided faces.
• The adenovirus is an example of an icosahedron.
• The herpes simplex virus is an example of a polyhedral (icosahedral) virus that is also enveloped.

Front 39

define: complex

Back 39

• viruses that have a complex structure fall into this category
• Most of these viruses are bacterial viruses (bacteriophages).
• The poxvirus which are animal viruses also fall into this category as they do not possess capsids that are readily identified

Front 40

How are viral classification schemes classified?

Back 40

they are classified based upon the disease that they produce
• meningitis virus
• pneumonia virus
• hepatitis virus