Topic 2 Molecular Genetics: Molecular Genetics of Viruses

Question 1

• Consists of the following

Answer 1

1. Virus

Question 2

a. Nucleic Acid
b. Capsid
c. Capsomeres
d. Viral envelope

Answer 2

Parts of Virus

Question 3

• RNA or DNA that can be double or single stranded

Answer 3

a. Nucleic Acid

Question 4

• A protein coat that encloses the nucleic acid

Answer 4

b. Capsid

Question 5

• Assemble to form the capsid

Answer 5

c. Capsomeres

Question 6

• Surrounds capsid of some viruses and incorporates phospholipids and proteins obtained from the cell membrane of the host

Answer 6

d. Viral Envelope

Question 7

• A virus that only attacks bacteria, is usually specific to a type of cell via viral surface proteins binding to specific receptors on the host cell of the species.

Answer 7

2. Bacteriophage

Question 8

• Host range is a term used to define the range of organisms or species a virus can attack

Answer 8

Note

Question 9

• There are two cycles a virus can take when it needs to replicate

Answer 9

3. Viral Replication

Question 10

a. Lytic Cycle

b. Lysogenic Cycle

Answer 10

Types of Viral Replication

Question 11

• When the virus penetrates the host cell membrane and uses host machinery to produce nucleic acids and viral proteins that are then assembled to make new viruses
  a. These viruses then burst out of the cell and infect other cells
  b. DNA viruses - replicate by first replicating DNA and forming new viral DNA, which is then transcribed to produce viral proteins that combine with DNA to form new viruses
  c. RNA virus - RNA serves as mRNA which is translated into protein. This protein and RNA assemble to form a new RNA virus
  d. Retroviruses - single stranded RNA viruses that use reverse transcriptase to make a DNA complement of their RNA by hijacking the host cell’s replicating machinery. This RNA is then used to manufacture mRNA or enter the lysogenic cycle (becoming incorporated into the host DNA) (i) A common example of a retrovirus is HIV

Answer 11

a. Lytic Cycle

Question 12

• When viral DNA is incorporated into the DNA of the host cell; there are two phases to the lysogenic cycle:
  a. Dormant stage - the virus is referred to as a provirus (prophage if a bacteriophage) and remains inactive until an external stimuli triggers the virus
  b. When triggered, the virus enters the lytic cycle, and follows the same steps as mentioned in the previous bullet

Answer 12

b. Lysogenic Cycle

Question 13

• When a bacteriophage integrates itself into the host genome, it is a prophage, not an episome!

Answer 13

Note

Question 14

• Are not viruses or cells, but are infectious, mis-folded versions of proteins in the brain that cause normal versions of proteins to also become mis-folded. Prions are fatal, and are implicated in diseases such as Mad Cow disease, kuru, scrapie in sheep, and Creutzfeldt-Jakob disease

Answer 14

4. Porins

Question 15

• Very small (even smaller than viruses!) circular RNA molecules that infect plants. These do not encode for proteins, but replicate in host plant cells via host enzymes, and cause errors in the regulatory systems of plant growth

Answer 15

5. Viroids