Viruses, Structure, Growth and Taxonomy

Question 1

Size of Viruses

Answer 1

Small (20-250nm)

Question 2

Microscope needed to see viruses vs bacteria

Answer 2

Light microscope shows only bacteria but electron microscope shows both

Question 3

Obligate vs facultative intracellular paracsites

Answer 3

Obligate cannot reproduce outside host cells - so basically viruses

Facultative can reproduce either inside or outside cells like some bacteria (e.g. mycobacteria or some fungae)

Question 4

Capsid

Answer 4

Protein shell of a virus that encloses its genetic material; consists of oligomeric structural subunits called protomers;

It is different to an envelope as that is a membrane made of lipids

Question 5

Describe nucleic acids of viruses

Answer 5

DNA (may be double or single stranded circular or linear)
3kb-200kb (kilo base)

RNA (ds or ss; ss may be +ve or -ve polarity; linear or segmented)
5kb-10kb

Question 6

Helical vs Icosahedral Capsid

Answer 6

Capsids have a form of symmetry::

Icosahedral far more prevalent

Question 7

Roles of Viral Proteins

Answer 7

Capsid/Capsid Formation

Attachment between viral ligand and cell receptor to determine viral tropism

Enzymes mostly involved in macromolecular synthesis

Interference with cell function (e.g. apoptosis or immune function)

Question 8

Factors to consider in viral taxonomy

Answer 8

Nature of genetic material

Nature of capsid

Enveloped or not

Size and shape

Question 9

Steps in viral replication

Answer 9

Attachment to cell receptor

Entry (endocytosis or membrane fusion)

Uncoating

Macromolecular synthesis (multiple copies of virl genome and protein, requires mRNA)

Assembly

Release (Budding, cell lysis)

Question 10

Virion

Answer 10

Entire virus particle consisting of capsid and nucleic acids ++

Question 11

Positive and Negative sense RNA

Answer 11

Positive is very similar to mRNA so can be directly translated but negative is complimentary so must be converted to positive by an RNAP before translation

Question 12

The Baltimore classification of viral replication and how they become mRNA

Answer 12

Viral classification strategy based on genome and replication strategy

Question 13

Reverse Transcriptase

Answer 13

RNA dependent DNAP::

It is a DNAP that transcribes single-stranded RNA into DNA

Question 14

Retrovirus

Answer 14

Virus that uses RNA as its genetic material; it makes a DNA copy of its genome once infecting and inserts that INTO the host cell’s DNA (part of why HIV is so hard to cure)