MICR 2420 Lecture 7: MICR 2420 Lecture 7

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27 Jun 2018

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Chapter 6.3: Viral Genome & Classification

Viral genomes

Usually very simple, and genes are efficiently packaged

RNA/DNA

Single or double stranded

Linear or circular

Bacteria phages usually have double stranded DNA

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Giant viruses

Genome of double stranded DNA, 500-2500 genes

Mimi virus (relative of mama virus)

oInfects ameba

omay cause human pneumonia,

obacterium sized genome of 1.2 million base pairs encoding ~ 1000 genes

oInfected by small virus (sputnik virophage, virus eater)

Pithovirus

oIsolated from tundra frozen for 30,000 years

oSize of bacteria E.Coli

Siberian giant virus – Mollivirus sibericum

oFirst virus shown to contain parts of ribosome

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How are viruses classified?

The International Committee on Taxonomy of Viruses has devised a classification system

based on:

Genome composition- including its nature, shape, strandedness and whether it is

segmented

Capsid symmetry

Envelope (presence or absence, and structure, if present)

Size of virus particle (range from 30-400nm across; related viruses tend to be similar in

size

Host range (not always very useful)

Genome classification of viruses

Considered to be the most important criterion

The Baltimore Virus Classification system is the most widely used and accepted

oRemember: ALL cells and viruses need to make mRNA to produce their

fundamental protein constituents

omRNA needs to be produced from the viral genome inside the host

How mRNA is produced by a virus is central to the Baltimore Virus Classification

System

oSo far, 7 fundamental ways are described...

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Document Summary

Usually very simple, and genes are efficiently packaged. Bacteria phages usually have double stranded dna. Genome of double stranded dna, 500-2500 genes. Mimi virus (relative of mama virus: infects ameba, may cause human pneumonia, bacterium sized genome of 1. 2 million base pairs encoding ~ 1000 genes, infected by small virus (sputnik virophage, virus eater) Pithovirus: isolated from tundra frozen for 30,000 years, size of bacteria e. coli. Siberian giant virus mollivirus sibericum: first virus shown to contain parts of ribosome. The international committee on taxonomy of viruses has devised a classification system based on: Genome composition- including its nature, shape, strandedness and whether it is segmented. Envelope (presence or absence, and structure, if present) Size of virus particle (range from 30-400nm across; related viruses tend to be similar in size. Considered to be the most important criterion. How mrna is produced by a virus is central to the baltimore virus classification.

Related Questions

QUESTION 1: The rabies virus primarily affects the nervous system. The specificity that the rabies virus has for neuronal host cells is primarily dictated by __________________________.

A. the helical shape of its viral capsid

B. the type of nucleic acid used for its viral genome (single-stranded, antisense RNA)

C. the spikes that protrude from its viral envelope

D. the segmented nature of its viral genome

QUESTION 2: Which of the following genome types has been observed in viruses? To be marked correct, you'll need to select all true statements, as there may be more than one correct answer.

A. Single-stranded RNA

B. Single-stranded DNA

C. Double-stranded RNA

D. Protein-based

QUESTION 3: Choose the correct statement about viral evolution.

A. RNA and DNA viral genomes evolve at equal rates.

B. Cellular genomes mutate at a faster rate than viral genomes due to their large size and increased chance of replicative mistakes.

C. DNA viruses mutate faster than RNA viruses because thymine is more susceptible to mutation than uracil.

D. RNA viruses mutate faster than DNA viruses due to a lack of proofreading replicative enzymes.

QUESTION 4: Your elderly patient is affected by shingles. After careful observation, you note that the virus responsible for the infection has an icosahedral capsid, is enveloped, and has double-stranded linear DNA as its genetic material. Based on this information, in which of the following viral families would you group this viral pathogen?

QUESTION 5: Which of the following is a key difference between lytic and lysogenic bacteriophage replication cycles?

A. Lysogenic bacteriophages release via host cell lysis, whereas lytic bacteriophages bud off from the host cell membrane.

B. The lytic replication cycle ends with host cell lysis and release of newly formed bacteriophage particles, whereas lysogenic replication leads to prophage formation.

C. Lytic replication requires an uncoating step, whereas in lysogenic replication, the bacteriophage's nucleic acid is directly injected into the host cell.

D. Whereas lytic replication enables the infection of several hosts, lysogenic replication only allows for infection of a single host cell.

QUESTION 6: Which of the following is an unsuitable culture method for an animal virus?

A. Direct inoculation of virus onto blood agar

B. Live animal inoculation

C. Tissue culture method

D. Injection of virus into embryonated eggs

28. Which two of the following statements is NOT true?

A) Eukaryotes have larger genomes and more genes than prokaryotes

B) Multicellular eukaryotes have larger genomes and more genes than single celled eukaryotes

C) Genes derived from both bacteria and archaea can be found in eukaryote genomes

D) Most eukaryotic genomic DNA is packaged into linear chromosomes

E) Mitochondrial genomes of eukaryotes are circular .

F) They include LINES, SINES, and Alu elements

G) They can cause mutations

H) Transposons are associated with genetic diseases

I) Transposon movement is restricted to meiosis

J) Special repeated elements found in the telomeres are beneficial to humans

The DNA of bacteriophage l is a linear double-stranded molecule that has complementary single-stranded ends. These molecules can form closed circular molecules when two âcohesiveâ ends on the same molecule join, and they can form linear dimers, trimers, or longer molecules when sites on different molecules are joined.

a) What conditions should be chosen to ensure that l phage DNA molecules form closed circular monomers, as opposed to dimers, trimers, etc?

b) Under certain, l phage DNA molecules are infective. When a very low concentration of l phage DNA is incubated with DNA polymerase I and the four deoxyribonucleoside triphosphates, the infectious activity of l phage DNA is destroyed. Brief treatment of l phage DNA with bacterial exonuclease III, an enzyme that removes 5â-mononucleotides from the 3â-ends of double-stranded DNA molecules, also destroys infectivity, but subsequent treatment of the DNA with DNA polymerase and nucleotide substrates can restore infectivity. What does this tell you about the structure of the cohesive ends of the DNA? Explain the effects of the two enzymes.

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MICR 2420 Lecture 7: MICR 2420 Lecture 7

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