Viruses, structure, growth and taxonomy

Question 1

Why are viruses filterable

Answer 1

Because they’re small

Question 2

Structure of viruses

Answer 2

• Simple
• nucleic acid
• proteins
• Some have lipids

Question 3

Properties of viruses

Answer 3

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

Question 4

Where does replication occur in a eukaryotic cell of a virus

Answer 4

Nucleic acid and protein synthesis may be in different parts of host cells

Question 5

What do mature virus particles have

Answer 5

Nucleic acid (genome)
Protein coat (capsid)
Some have lipid coat (envelope)

Question 6

Different type of nucleic acids that viruses can have

Answer 6

DNA or RNA

Question 7

What can the nucleic acid in a virus have

Answer 7

Negative polarity or positive polarity

Question 8

How are positively polar nucleic acids different from negatively polar nucleic acids

Answer 8

Positive ones can go straight to ribosome and build proteins

Negative ones have to be copied to complementary sequence so it can be positive and go to the ribosome

Question 9

Functions of protein within a viral cell

Answer 9

• Formation of capsid
• Attachment (specific interaction between viral ligand and cellular receptors)

(viral ligands are proteins on surface)

Question 10

Whats tropism

Answer 10

Ability to only inject certain types of cell

Question 11

what do many viral proteins do to cell function and how is this useful

Answer 11

Interfere with it (e.g. have protein to stop apoptosis as cells would normally start apoptosis if they are infected)

Question 12

What is the lipid envelope derived from

Answer 12

Host cell membranes

Question 13

What does the lipid envelope contain

Answer 13

external attachment proteins

Question 14

How are viruses classified

Answer 14

Families—> genea—> strains

Question 15

Is RNA in viruses double or single stranded

Answer 15

Can be both. The single stranded RNA can be -ve or +ve

Question 16

What can the capsid be like in a virus

Answer 16

Isocahedral/helical

Question 17

First 3 steps of viral replication

Answer 17

1) attachment
2) Entry (via endocytosis for some or via fusion by those with lipids on surface
3) Uncoating (where the nucleic acid leaves the lipid envelope and capsid)

Question 18

How does uncoating happen

Answer 18

When endocytosed int the cell, becomes vesicle. Vesicle goes to the lysosome and lysosome releases nucleic acid

Question 19

Steps of how copies of the genome are produced in a viral cell

Answer 19

Macromolecular synthesis

• MUltiple copies of viral genome and proteins
• Needs to produce +ve single stranded RNA (i.e. mRNA)

Question 20

For viruses with -ve single stranded RNA, what must they contain and why

Answer 20

Contain genome which codes for RNA polymerase so you can make complementary +ve strand of -ve RNA

Question 21

What do viruses that have double stranded DNA need to do

Answer 21

Eukaryote will produce +ve RNA

Question 22

What do viruses with single stranded DNA need to do

Answer 22

Synthesis of complementary strand to make double stranded DNA and so cell can then transcribe it

Question 23

What does a retrovirus do

Answer 23

Single stranded +ve RNA—-> Reverse transcriptase turns it into single stranded DNA and then there is synthesis of the other strand of DNA

Question 24

Why are retroviruses beneficial

Answer 24

Turns RNA to DNA which incorporates in host cell chromosome so whenever the cell divides, virus is part of it

Question 25

5th and 6th step of virus replication

Answer 25

6) assembly
7) release;
- Budding (yields enveloped virus)
- Cell lysis (cytolysis)