Virus As Infectious Agents

Question 1

What are viruses?

Answer 1

An infectious agent which consists of nucleic acid contained within a protective protein coat that protects its genetic being
Infect prokaryotes and eukaryotes

Question 2

Difference between bacteria and virus

Answer 2

Viruses are not affected by antibiotics
Viruses are not “alive” : CANNOT replicate outwith a cellular environment – produced by assembly of preformed components : ‘obligate intracellular parasites’ : lack critical components (eg energy, machinery for self sufficient propagation)

Question 3

Vision (what are the virus particle structures)

Answer 3

Genome (virus nuclei acid) + capsid (virus-encoded proteins) make up nucleocaspid
Some viruses also have envelope (lipid belayer derived from cellular membranes)

Question 4

2 types of virus symmetry shapes

Answer 4

Icosahedral
Helical

Question 5

Describe properties of icosahedral shape of viruses

Answer 5

20 faces each face an equilateral triangle
axes of 2-, 3- and 5-fold rotational symmetry
Capsomer structure enclosing maximum volume
Formed from repeated subunits
Some are enveloped

Question 6

Describe properties of helical shape of virus

Answer 6

Coiled, telephone cord-like appearance
Provides protection for genome without need to encode multiple capsid proteins
All helical symmetry viruses are enveloped

Question 7

What is advantageous about a virus having symmetry?

Answer 7

Saves genetic space; few genes copied MANY times

Question 8

Function of the envelope in a virus

Answer 8

Protects genome from being harmed which would destroy its ability to make templates of itself
Facilitates binding & entry of viruses into cells and release of genome in cell

Question 9

Proteins/structures within envelope/capsid of virus are a major target of…

Answer 9

Immune response

Question 10

What are virus genomes

Answer 10

-Genetic “heritage”, biological material that they need to be able to replicate
-Codes for virus functions proteins) required for replication and interaction with host

Question 11

Virus genome properties
-made of…
-single or double stranded?
-shape? Segments?
-size

Answer 11

-DNA or RNA (never both)
-single or double
-linear or circular
-segmented or non segmented
-2-300kbp

Question 12

List the virus classification in order

Answer 12

Order—>family—>subfamily—>genus—>common species name

Question 13

What is viruses aim?

Answer 13

To reproduce its genetic material

Question 14

To multiply viruses must…

Answer 14

Infect cells

Question 15

Do all viruses exploit host cell in the same way to replicate?

Answer 15

Nah

Question 16

Name the steps of virus replication

Answer 16

1a) attachment
1b) penetration
1c) uncoating

2) gene expression and genome replication

3) assembly and exit

Question 17

Describe each step of virus replication

Answer 17

1a) attachment: virus anti receptors interact with cellular receptors
1b) penetration: receptor mediated endocytosis—> fusion with lipid bilayer of plasma membrane
1c) uncoating: partial/total disruption of virus particle to facilitate gene expression- can occur in cytoplasm or nucleus depending on site of replication
2) gene expression and genome replication: replicate in different cellular compartments depending on what type it is; most DNA viruses replicate in nucleus (not pox), most RNA viruses explicate in cytoplasm (not retro, orthodomy)
3) assembly and exit:exit by;
-simple release
-release by budding
-release by exocytosis which damages cell causing it to lyse