Part 3

Question 1

Describe the central dogma of viruses?

Answer 1

• sometimes bacteria have a genome that is composed of DNA or RNA and it can be either single/double stranded. So this creates a problem when trying to put all bacteria under one central dogma pathway.
• It will not be the same for all viruses.
  This is where the Baltimore classification system

Question 2

How is the Baltimore Classification System used to group bacteria?

Answer 2

• there are three broad categories viruses can be placed into:
• DNA viruses: have a DNA genome and use the host cells DNA polymerase to replicate their genome and the hosts RNA polymerase to transcribe their genome
• ——————————————————————————- RNA viruses: have RNA genome, either single or double stranded. Use a special RNA polymerase, RNA dependent RNA polymerase.
• Reverse-transcribing viruses: carries viral enzymes that is called reverse transcriptase, that is capable of using RNA as a template to make DNA.
• There are two sub categories, that differ in what their initial genome is.

Question 3

Describe the sub-categories of the DNA viruses?

Answer 3

• class 1: single stranded DNA genome
• class 2: doubled stranded DNA genome
  ( they use the host cells DNA polymerase to replicate the viral genome and the host cell also provides RNA polymerase to make the mRNA for the viral genome.-papilloma virus)

Question 4

Describe the sub-categories of the RNA viruses?

Answer 4

• • Have an RNA genome and Use a special RNA polymerase, RNA dependent RNA polymerase, that they provide.
• This is an enzyme, that uses RNA as a template to make a complementary to make anther RNA.
  ( we’ve only studied RNA polymerase that is DNA dependent.)
  ——————————————————————————–
• ## Class 3: double stranded RNA genome.
• ## Class 4: single stranded plus genome, which means it is sequence as the mRNA, so the viral genome can be translated directly by the cell. It is technically an effective mRNA . But to make more copies of the viral genome you need RNA dependent RNA polymerase.
• Class 5: single stranded minus genome, which would be like Ebola, Measles. The minus strand indicates that is not the same sequence as the mRNA, but it is complementary. This also carries RNA dependent RNA polymerase.

Question 5

Describe the sub-categories of the Reverse-transcribing viruses?

Answer 5

class 6: retro viruses-has an enzyme called reverse transcriptase and has an RNA genome. It also contains a plus. This indicates that it has the same sequence as the mRNA.
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class 7- double stranded DNA genome, but the carry around the same reverse transcriptase. Hep-B is an example but are also found in lots of plant viruses.

Question 6

What is reverse transcriptase?

Answer 6

• an enzyme that uses RNA as a template to make DNA. (RNA dependent DNA polymerase.)
• createes cDNA, then geos back in the other direction and degrades the RNA and synthesis the complementary cDNA to make a double stranded molecule.

Question 7

What is cDNA?

- what are its purposes, both in theory and most commonly.

Answer 7

DNA that has been made from an RNA template.

• in theory be used for the following: be used directly as a template for transcription, or be used as a template for RNA polymerase to make more copies of the viral genome.
• MOST COMMONLY: this will be inserted into the host cells genome and then remain latent, and later be used to be transcribed to start making the viral mRNA which is used to make more copies of the viral genome.

Question 8

Do viruses use sexual reproduction?

Answer 8

They have the ability to share genetic information between strains, if two related strains infect a host cell at the same time, which is known as GENOMIC REASSORTMENT.
- very common in viruses like the flu.

Question 9

Describe the influenzas virus example and how it relates to genomic reassortment?

Answer 9

• slightly different strains of influenza viruses come to a host cell, they differ slightly in their genetic composition, but there both capable of infecting the same type of host cell.
• both genomes are copied to make mRNA and proteins.
• when the new viral particles are made they are in a mixture or a recombination of the two original strains.
• This type of recombination generates a much more pathogenic genome.

Question 10

How do new virions escape once they have assembled?

enveloped

Answer 10

• virion pushes up against the cell membrane and triggers an exocytosis event, or to bud off a little piece. This is how the virus picks up its phospholipid bilayer as it exists the cell.
  ( BUDDING)

Question 11

How do new virions escape once they have assembled?

non-enveloped

Answer 11

• they exit via a process called bursting: The virions brake the membrane or the cell wall and then they are shed outside the cell into the surrounding environment.