BIO 370 Lecture Notes - Lecture 34: Rna Virus, Messenger Rna, Reverse Transcriptase
Eolutioar Mediie Rules from Evolutionary Biology
• Observations on emerging viruses:
– Reservoir is in a NON-human host (monkeys, bats, birds, etc.)
– EVOLVES into a form compatible with a human host.
– Almost always RNA viruses. Why?
• RNA viruses lack the ability to correct mutation errors and thus mutate much more
rapidly than other infectious organisms.
What is a virus?
• A nucleic acid coated in protein (or sometimes a lipid).
• Viruses hae o ellular ahier of their o ad ust use a host ell’s machinery to
be reproduced, emerge and repeat the cycle (and that is pretty much all that viruses do
– get reproduced).
Some common viruses
• Single stranded DNA viruses (parvoviruses)
• Double stranded DNA viruses (notably herpes and herpes-like viruses such as
chickenpox)
• Single stranded RNA viruses (poliovirus)
• Double stranded RNA viruses (rotaviruses: gastroenteritis in young children)
Virus Types Regarding Heredity
• DNA viruses
– DNA as hereditary material > copied and transcribed by standard processes.
• RNA viruses
– Positive sense
• translated directly into protein like messenger RNA
– Antisense
• copied into Positive Sense then translated
– Retroviruses
• RNA as hereditary material, but reverse transcribede into DNA and
incorporated into genome of host
That RNA viruses utilize Uracil rather than
Thymine makes them more prone to mutation
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Cytosine Uracil
3 H bonds 2 H bonds (usually)
Pairs with Guanine Pairs with Adenine (mostly)
Cytosine can de-aminate or lose the amine (ammonia-like) group, to become Uracil
What does this mean for RNA viruses?
• DNA viruses
– Not so much
– Cytosine to Uracil chemical transformation detectable and fixable
• RNA viruses
– Cytosine to Uracil chemical transformation undetectable
– Mutations more likely
Polymerase and transcriptase properties also result in higher mutation in RNA viruses
• DNA viruses
– DNA polymerase generally pretty good at proofreading
• RNA viruses
– RNA polymerase not as good at proofreading as DNA polymerase
• Retroviruses
– Reverse transcriptase has no capacity to proofread
• every mistake is kept, virus either functions or it does not.
Zika Virus Factoids
• A single-stranded positive sense RNA virus of about 11,000 bases
• Related to viruses that cause dengue fever, West Nile virus disease, and Yellow Fever.
– Genus Flavivirus, Family Flaviviridae
• First isolated from Zika Forest in Uganda in 1947
• Occurred in a narrow equatorial belt in Africa and Asia, until it began spreading across
Pacific in 2011.
• 11% difference among strains
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Document Summary
(cid:862)e(cid:448)olutio(cid:374)ar(cid:455) medi(cid:272)i(cid:374)e(cid:863) rules from evolutionary biology: observations on emerging viruses: Reservoir is in a non-human host (monkeys, bats, birds, etc. ) Evolves into a form compatible with a human host. Why: rna viruses lack the ability to correct mutation errors and thus mutate much more rapidly than other infectious organisms. Some common viruses: single stranded dna viruses (parvoviruses, double stranded dna viruses (notably herpes and herpes-like viruses such as chickenpox, single stranded rna viruses (poliovirus, double stranded rna viruses (rotaviruses: gastroenteritis in young children) Dna as hereditary material > copied and transcribed by standard processes: rna as hereditary material, but reverse transcribede into dna and incorporated into genome of host. Thymine makes them more prone to mutation: dna viruses, rna viruses. Retroviruses translated directly into protein like messenger rna copied into positive sense then translated. Cytosine can de-aminate or lose the amine (ammonia-like) group, to become uracil. Cytosine to uracil chemical transformation detectable and fixable.
