A2.3 Viruses (HL)

Question 1

Why are there many types of viruses?

Answer 1

they did not come from a single common ancestor

Question 2

What does convergent evolution mean?

Answer 2

share some common features as they evolved to do similar functions

Question 3

Describe the features/similarities between viruses

Answer 3

• small size
  
  • most are 20 to 300nm in diameter
• fixed size
  
  • will not grow like other organisms
• no cytoplasm and no (or very few) enzymes
  
  • e.g. reverse transcriptase of the HIV virus

Question 4

What genetic material do viruses have?

Answer 4

• double or single stranded DNA (aka DNA virus)
• double or single stranded RNA (aka RNA virus)

Question 5

Does virus use the universal genetic code

Answer 5

Yes

• still uses the universal genetic code like other organisms on earth
  
  • ATGC (DNA)
  • AUGC (RNA)

Question 6

A single stranded RNA virus can do what? (Describe)

Answer 6

• use its RNA directly as a messenger RNA (mRNA) that is translated by the host cell to make viral proteins (positive-sense RNA virus)
  
  • requires another enzyme to convert its RNA into mRNA, which is then used by the host cell (negative-sense RNA virus)
  • converts its RNA into double stranded DNA and then use it to make mRNA (retrovirus)

Question 7

What is a “capsid”

Answer 7

a protein coat that encloses the genetic material of the virus

Question 8

What is a “naked capsid”

Answer 8

no membrane or envelope outside the protein coat

Question 9

What is a “enveloped capsid”

Answer 9

has a cell membrane that surrounds the protein coat

Question 10

How can you tell whether a virus has an enveloped capsid or not

Answer 10

whether they have an envelope depends on how the virus replicates

Question 11

What does bacteriophage do and give an example

Answer 11

attacks ONLY bacteria

example: bacteriophage lambda

Question 12

Describe the lytic cycle

Answer 12

AERTSLS
1. attachment
2. dna entry
3. dna replication
4. dna transcription
5. protein synthesis
6. lysis
7. spread

the virus attaches to a host cell

binds to a receptor - access to attach

inject dna or rna into the cell, depending on what genetic material it has

takes genetic material from virus

make copies of virus

cells use own resources

cause cell membrane of cell to rupture - viral copies go and infect other cells

Question 13

Describe the lysogenic cycle

Answer 13

AEIC

1. attachment
2. dna entry
3. integration
4. cell division

inject genetic material - stays hidden in the host genetic material

when host makes new cell

replicates both own and viral genetic material

daughter cells do the same

becomes problem when virus triggered to go into the lytic cycle

Question 14

List the 7 steps of the lytic cycle

Answer 14

1. attachment
2. dna entry
3. dna replication
4. dna transcription
5. protein synthesis
6. lysis
7. spread

Question 15

List the 4 steps of the lysogenic cycle

Answer 15

1. attachment
2. dna entry
3. integration
4. cell division

Question 16

Which cycle is bacteria lambda able to go through

Answer 16

bacteria lambda has the ability to go thru both lytic and lysogenic

Question 17

Why does a virus have an envelope

Answer 17

• a virus usually forms the envelope when it bursts a cell
• the phospholipid that makes the cell membrane might cover the virus
• this is more common in viruses that affect animal cells because the envelope would help the virus infect the animal host cell
• viruses that infect bacteria or plant cells are usually non-enveloped. why?

Question 18

Is coronavirus enveloped or naked

Answer 18

enveloped

Question 19

Is bacteriophage lambda enveloped or naked

Answer 19

naked

Question 20

Is HIV enveloped or naked

Answer 20

enveloped

Question 21

What are Retrotransposons?

Answer 21

• sequences of nucleotides that occur widely in the genomes of eukaryotes
• when it is transcribed to produce RNA, this RNA is translated and several enzymes are produced
• enzymes make more DNA copies of the transposon by reverse transcription of the RNA
• then insert these copes into the cell’s chromosomes in random positions