Virus Structure Growth And Taxonomy

Question 1

Size

Answer 1

Small;
20-250nm;
Electron microscopy;
Filterable agents

Question 2

Structure

Answer 2

Simple;
Nucleic acids
Proteins;
Lipids;
No organelles;

Question 3

Metabolism

Answer 3

Metabolically inert;
Rely on host cell;
Obligate intracellular parasites;

Question 4

Replication

Answer 4

Independent synthesis of component parts;
May be in different parts of cell;
Under separate control;
Subsequent assembly into new particles;

Question 5

Viral components include

Answer 5

Nucleic acid (genome);
Protein coat (capsid);
Lipid envelope;

Question 6

Viral component:nucleic acid

Answer 6

DNA and RNA;

DNA:
Double and single stranded;
Circular or linear;
3kb to 200kb;

RNA:
Double or single stranded;
Linear or segmented;
5kb to 10kb;
Positive or negative polarity

Question 7

Viral component: proteins

Answer 7

Capsid formation - symmetry - helical or icosahedral;
Attachment - interaction between viral ligand and cellular receptor;
Determines viral tropism;
Enzymes - macromolecular synthesis;
Interference with cell function - to stop apoptosis, to avoid immune recognition;

Question 8

Viral components: lipid envelope

Answer 8

Derived from host cell membranes;
Must have external attachment proteins;
Stripping of envelope leads to loss of infectivity;
Enveloped viruses - more fragile;

Question 9

Virus classification

Answer 9

Nature of genetic material;
Nature of capsid;
Size and shape;
Families, genera, strains;
Enveloped or not?

Question 10

Viral replication

Answer 10

1. Attachment - viral ligand/cellular receptor;
2. Entry - endocytosis; fusion;
3. Uncoating;
4. Macromolecular synthesis -
   Multiple copies of viral genome;
   Multiple copies of viral protein -
   Requires production of positive single stranded rna (mRNA);
   Baltimore classification;
5. Assembly
6. Release
   Budding (yields enveloped virus);
   Cell lysis;