LEC 7 - Virus Structure + Function I Flashcards by Raegan Chambers

What are all viruses when it comes to being a parasite?

Obligate Intracellular Parasites

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What makes a virus a virus, making it different from bacteria?

No independent metabolism

Host provides ribosomes + energy + all precursor molecules

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What does the small size of a virus allow for when it comes to entering a host cell?

Filterable agents

Passage through fine pore filters can occur

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What is different about the viral replication when compared to other living organisms?

Progeny are created in an assembly line

Then quickly released into the host

NO BINARY FISSION

Latent period > Rise > Yeild

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What is occurring in the cell during the latent period?

Replication

Assembly

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What are viruses generally made of?

Nucleic acids

Proteins

Lipid-containing envelope

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What is the principal component of a virus?

Proteins

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What are the special enzymes that virus encodes for itself?

RNA dependent RNA polymerases for the negative strand RNA virus

Reverses transcriptase for retroviruses

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Where are the special viral enzymes encoded?

Within the capsid

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Term: Capsid

Protein covering surrounding core of nucleic acid + enzymes

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Term: Capsomeres

Small protein subunits typically composed of several small proteins that combine in groups to form the capsid

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Term: Virion

Complete virus particle

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Term: Envelope

Membrane-like outer covering of certain viruses

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Term: Spikes

Cirus proteins embedded in envelope that project from surface

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What is the envelope made of?

Combination of host membrane with some virus proteins

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What is often associated with spikes on a virus?

Enzymatic activities

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What are the two patterns seen in the nucleic acid genome?

Extended nucleic acid form

Condensed nucleic acid form

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What is the viral genome made of?

RNA

DNA

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What are the forms of the viral RNA/DNA?

Double stranded

Single stranded

Segmented

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Which is more stable, DNA or RNA?

DNA

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What is the positive of having RNA as your genome?

Increased rate of replication

Which allows for more mutations, allowing the virus to adapt to the environment more easily

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What are the characteristics of positive stranded RNA?

Can serve as mRNA directly

Directly translated by host ribosomes into proteins

Hosts understands

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What are the characteristics of negative stranded RNA?

Must first be transcribed

Via virus-encoded RNA dependent RNA polymerase

Then becomes a positive strand

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What is known about viral ancestory?

They do not share a common one

What are the two features that are used to discribe a virus?

Physical features Biological properties

What physical features are used to describe virus?

Nature + Physical form of nucleic acid genome Capsid structure + symmetry Presence/absence of envelope

What biological properties are used to describe viruses?

Host range Transmission mechanism Tissue tropism Pattern of replication

What phase must all virsuses pass through?

mRNA phase

What are the basic steps in viral replication?

Attachment Latent period Burst/Release by budding of progeny virions

What is occurring during the latent period?

Virus is developing inside the cell but is not readily evident outside the cell

What occurs with the cell when a true burst occurs?

Death of the host cell

Where do DNA viruses tend to repicate and mature in the host?

Within the nucleus

How do some DNA viruses disrupt the host cell cycle?

Change the control of p53 or Rb Enters "S-like" phase to replicate

What is different about the replication process of large, complex DNA viruses?

Dont pay attention to host cell cycle Supply their own host cell-independent DNA replication functions

Where does the virus go to be released out of the cell by exocytosis

Endoplasmic reticulum

Where do RNA viruses tend to replicate and mature in the host?

Cytoplasm

What is a common problem amoungst RNA viruses?

RNA is unstable Molecules must be copied rapidly and the host doesn't have the machienery to do so

What are the ways an RNA virus handles the issue of the host cell not being able to replicate it?

Transport molecules into the host in virion itself -- or -- Synthesized from virus genome

What are negative RNA strands need to be read?

RNA-dependent RNA polymerase (transcription)

How is RNA-dependent RNA polymerase made?

Place it within the capsid Transport pre-formed into the host to start infection

What are the three viruses that can move retrograde through neurons?

Rabies Herpes Polio

What are the hallmarks of retroviral replication?

Reverse transcription -- and -- Integration

How are retroviruses handled within the host cell?

Pseudo-diploid RNA virus Convert RNA to DNA (reverse transcription)

Term: Destructive replication

One double stranded DNA is substituted for two molecules of single stranded RNA that originally entered the cell

What enzyme does the retrovirus need that it encodes for?

Reverse transcriptase | (RNA-dependent DNA polymerase)

What does reverse transcriptase do?

Reverses the flow of genetic information Allows DNA to be made from RNA

How does knowing the process of transmission lead to better control?

Effective control often hinges on breaking the chain of transmission

Term: Transformation (cancer + virus)

Host cells converted to malignant conditions

What does a host cell do to transform into a malignant condition?

Become immortal Continue to divide w/o any control Alter morphology Lose contact inhibition

What are the critical mechanisms when it comes to a cell transforming into a malignant cell line?

Inactivation of cell cycle control mechanisms Providing genese that alter host behavior Enhancing transcription of key host genes involved in growth Preventing host from inducing apoptosis

What cell types does transformation normally occur in?

Non-permissive host cells

What happens if the virus is able to proceed through a full growth cycle?

Host cell will die

How do DNA tumor viruses alter the funciton of p53 or Rb?

Produce proteins that antagonize the function of the proteins Stopping them from suppressing growth

What are the "three" methods by which retrovirus transformation occurs?

Acute transforming retroviruses Chronic transforming retroviruses Indirect method

How does the indirect method of retroviral transformation occur?

Induction of tissue damage produces mutations

Describe: Chronic transforming retroviruses

Activate expression of growth-stimulating host genes Slower induction of cancer

Describe: Acute transforming retrovirus

Bring in altered forms of genes involved in cell growth control Drive host out of balance Acute tumor induction

What are the oncogenes involved in acute transforming retrovirals?

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