Viruses, Viroids, and Prions

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RNA or DNA Virus

Do or do NOT have an envelope

Capsid shape

HOST they infect

Used for Virus Identification

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Bacteriophages

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Phages

Viruses that attack bacteria are called bacteriophage or just phage

T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

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T-phages

The most commonly studied T-phages are T4 and T7

They infect E. coli , an intestinal bacteria

Six small spikes at the base of a contractile tail are used to attach to the host cell

Inject viral DNA into cell

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Escherichia Coli Bacterium

T - EVEN PHAGES ATTACK THIS BACTERIUM

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T-Even Bacteriophages

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Diagram of T-4 Bacteriophage

Head with 20 triangular surfaces

Capsid contains DNA

Head & tail fibers made of protein

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Retroviruses

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Characteristics of Retroviruses

Contain RNA, not DNA

Family Retroviridae

Contain enzyme called Reverse Transcriptase

When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell

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ENZYME

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Retroviruses

The enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) using virus RNA as a template

RTase

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Retroviruses

HIV, the AIDS virus, is a retrovirus

Feline Leukemia Virus is also a retrovirus

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Viroids & Prions

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Viroids

Small, circular RNA molecules without a protein coat

Infect plants

Potato famine in Ireland

Resemble introns cut out of eukaryotic

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Prions