Module 4: Section 1B

Question 1

Baltimore system of grouping viruses

Answer 1

• Developed by David Baltimore
• Classified into 7 different groups

Question 2

International committee on taxonomy of viruses (ICTV)

Answer 2

Places over 2000 viruses in 6 orders, several families and 349 different genera

Question 3

Class I: Double stranded DNA synthesis

Answer 3

mRNA synthesis and genome replication follow the same process as the DNA of the host

Question 4

mRNA synthesis - Class I

Answer 4

Transcription of dsDNA with host machinery and translation of mRNA into proteins

Question 5

Genome replication - Class I

Answer 5

Replication of dsDNA genome with host’s machinery

Question 6

Class II: Single-stranded DNA genome

Answer 6

• Genome can be a positive or negative strand
• First step is producing dsDNA using the ssDNA as a template

Question 7

mRNA synthesis - Class II

Answer 7

dsDNA product is transcribed into mRNA with host machinery

Question 8

Genome replication - Class II

Answer 8

dsDNA is produced and replicated with host machinery and then the two strands are separated, generating ssDNA

Question 9

Class VII: Reverse transcribing double stranded DNA genome

Answer 9

• dsDNA genome is first filled in then used to make an RNA template
• RNA template is used in RT process to make ssDNA

Question 10

mRNA synthesis - Class VII

Answer 10

dsDNA is transcribed to produce mRNA transcripts which are then translated into proteins

Question 11

Genome replication - Class VII

Answer 11

• positive ssRNA template is reverse transcribed into ssDNA with viral reverse transcriptase
• ssDNA strand is then completed to produce new partially dsDNA genomes

Question 12

Class VI: Retroviruses

Answer 12

• ssDNA is reverse transcribed from RNA genome
• dsDNA is made with DNA polymerase and is integrated into the host genome

Question 13

mRNA synthesis - Class VI

Answer 13

dsDNA integrated into host genome is transcribed into mRNA, which is then translated into proteins

Question 14

Genome replication - Class VI

Answer 14

• Positive ssRNA is transcribed into ssDNA by viral reverse transcriptase
• dsDNA is produced from the ssDNA and then integrated into the host genome with viral integrase
• positive ssRNA is transcribed from the integrated dsDNA to produce new genomes

Question 15

mRNA synthesis - Class IV

Answer 15

positive ssRNA genome can be used as mRNA that can then be translated into proteins

Question 16

Genome replication - Class IV

Answer 16

Positive ssRNA is used to produce negative ssRNA which is then used as a template to produce new positive ssRNA genomes

Question 17

mRNA synthesis - Class V

Answer 17

Negative ssRNA genome is used as a template to produce positive single stranded mRNA, which is then translated into proteins

Question 18

Genome replication - Class V

Answer 18

Negative ssRNA is used to produce positive ssRNA which is used as a template to produce new negative ssRNA genomes

Question 19

mRNA synthesis - Class III

Answer 19

• dsRNA is separated into two single strands
• Positive ssRNA can be used as mRNA, which is translated into viral proteins

Question 20

Genome replication - Class III

Answer 20

Positive ssRNA can be used as a template to produce new dsRNA genomes

Question 21

Antigenic drift

Answer 21

• Slow, ongoing point mutations, especially in HA/NA, that slightly change antigens and drive seasonal strain variation

Question 22

Reverse Transcriptase (RT)

Answer 22

Reverse transcriptase converts the viral RNA genome into DNA inside the host cell; it lacks proofreading, so errors often occur during HIV replication

Question 23

HIV - Integration

Answer 23

After HIV’s RNA is converted to DNA, the double-stranded viral DNA enters the nucleus with the enzyme integrase and is inserted into the host’s chromosome as proviral DNA

Question 24

Proviral DNA Function

Answer 24

The proviral DNA uses the host cell’s machinery to make viral mRNAs and new genomes, which are assembled into virions that bud from the cell