Chapter 13 Viruses, Viroids, and Prions

CHAPTER 13: VIRUSES, VIROIDS, AND PRIONS

Exam 4 material

GENERAL CHARACTERISTICS OF VIRUSES

Virus is the Latin word for “poison”

1935Wendell Stanley isolated the Tobacco Mosaic virus for the first time

DEFINITION OF LIFE

A complex set of processes resulting from the actions of proteins specified by nucleic acids

“Viruses are not living things. Viruses are complicated assemblies of molecules, including proteins, nucleic acids, lipids, and carbohydrates, but on their own they can do nothing until they enter a living cell. Without cells, viruses would not be able to multiply. Therefore, viruses are not living things.”

Viruses are “alive” (able to multiply) when they enter a host organism

We will say that viruses are living, but they are not.

Obligate Intracellular parasite-must have a living host cell in order to multiply

ALL VIRUSES ARE O.I.Ps

FEATURES OF VIRUSES

Only one type of nucleic acidDNA or RNA (not both)

A protein coatMade of lipids, carbohydrates, proteins

• Must have a host cell• Uses the cells machinery to copy itself

• Makes specialized structures that can transfer the viral information to other cells

• Lack personal enzymes

• http://www.youtube.com/watch?v=s-HThHRV4uo

COMPARING PROKARYOTES & VIRUSES (P 387)

Prokaryotes Viruses

HOST RANGE

Viruses can have a host rangeA spectrum of host cells the virus can infect Viruses that infect bacteria are bacteriophages (phages)Outer surface of virus must chemically interact with specific receptor site on host cell

VIRAL SIZE

Viruses are very small compared to bacterial cells

Need an electron scanning microscope to view

VIRAL STRUCTURE

Virion = complete, fully developed, infectious viral particle composed of nucleic acid and surrounded by a protein coast that protects it from the environment

NUCLEIC ACID

Prokaryotes and Eukaryotes use RNA and DNA as genetic information

Viruses use RNA or DNA-not both It is single or double stranded

CAPSID AND ENVELOPE

Protein coat = capsid

Combination of lipid, proteins, and carbohydrates that convers the capsid = envelope

Capsids without envelopes = nonenveloped viruses

When a virus enters a host cell, the host antibodies are produced

An interaction between antibodies and virus’ should inactivate the virus

Some viruses escape antibodies and are able to change their surface proteins

Surface proteins are called spikes

This is why you can get the flu many different times

GENERAL MORPHOLOGY

Compare with prokaryotic morphology

Helical : long rods, hollow and cylindrical spirals

Polyhedral : many sided viruses

Complex : complicated structureMany bacteriophages

TAXONOMY OF VIRUSES

A viral species is a group of viruses sharing the same genetic information and ecological niche.

GROWING VIRUSES

Nonliving: needs a host cell

Difficult and expensive to

maintain cultures

Usually learn from

bacteriophages

plaque = clearing within a media

VIRAL MULTIPLICATION

http://www.youtube.com/watch?v=Rpj0emEGShQ

A virus must be able to invade a host

A virus must take over a host’s machinery

BACTERIOPHAGES

LYTIC CYCLE

1. attachment to receptor site

2. injects DNA/RNA into cell

3. host cell starts making viral copies of nucleic acid

4. bacteriophages are assembled inside host cell

5. host cell is lysed

LYSOGENIC CYLE

Process where cell is not lysed and is able to stay alive

FAMILIES OF VIRUSES PAGE 392-3

Paroviridae

Adenoviridae

Papovaviridae

Poxviridae

Herpesviridae

Hepadnaviridae

Picornaviridae

Orthomyxoviridae

Bunyaviridae

Arenaviridae

Retroviridae

Reoviridae

• Rhabdoviridae• Filoviridae• Paramyxoviridae• Deltaviridae• Caliciviridae• Togaviridae• Flaviviridae• Coronaviridiae

VIRUSES AND CANCER

Almost anything that can alter the genetic material of a eukaryotic cell has the potential to make a normal cell cancerous

HPV

Hepatitis B

Leukemia, Feline leukemia

VIRUSES AND INFECTIONS

Latent infection = infection capable of staying dormant until stimulus is applied

Chronic viral infection = long lasting viral infection that occurs over a gradual time period (usually fatal)

HerpesFever blisters/cold sores

Chicken poxshingles

PRIONS ????????

A prion is a proteinaceous infectious particle A protein that infects like a virus

These diseases run in families; however, they can’t be totally inherited

There is a lot that is not known about prions

• Mad Cow disease• Kuru• Creutzfeldt-Jakob disease• Fatal familial insomnia• Gerstmann-Straussler-Scheinker

syndrome

VIROIDS

Viroids are short pieces of RNA with no protein coat that does not code for any protein

They cause plant diseases

Much is still to be learned about these particles