Question

13. The envelope of a virus is derived from the host's                                                                                   

A. nucleic acids   

B. membrane structures          

C. cytoplasm       

D. genome

14. Specificity of viruses to different types of cells is due to______sites on the host cell.                  

A. prophage                   

B. receptor               

C. transduction                                                                                                             

D. penetration              

E. transcription

15. In the growth curve of plaque-forming units, the time from infection until lysis is known as_________.    A. Eclipse period   

B. Rise period              

C. Burst period            

D. Latent period

16. Negative-sense ssRNA viruses require which of the following enzymes for their replication?                                                                                                                                                                                                                                                                          

A. DNA polymerase                                                            

B. Lysozyme                                                                                                                        

C. RNA-dependent RNA transcriptase                           

D. Reverse transcriptase

Answer 1

13. Membranes are made up of mainly of lipids, proteins and sugars. Biological membranes are also called phospholipid bilayer due to the 2 layers of lipid molecules present. Virus makes use of this cell membrane to make itself an envelope such that it's able to enter the host.The viral envelope fuses with the host's membrane which allows the capsid and viral genome to enter and infect the host.Thus the envelope of a virus is derived from the host's :

Option B. Membrane structures.

14.There are attachment proteins in the capsid or glycoproteins embedded in the viral envelope that helps in the attachment of the virus to a specific receptor site on the host cell membrane. This specificity of attachment to the host by the virus determines which cells can be infected by which virus. Thus, Specificity of viruses to different types of cells is due to receptor sites on the host cell.So, the answer is:

Option B. receptor.

15. In eclipse period, no mature virus progeny is produced.At the end of eclipse period, the mature phages start accumulating intracellularly until they are released by cell lysis. The time from infection until lysis is known as Latent Period. Rise period is when the number of free phages released into the medium through lysis keeps on increasing until it reaches a constant number at the end of the replication cycle.Thus, the time from infection until lysis is known as:

Option D. Latent period.

16. For replication Negative-sense ssRNA viruses need a RNA polymerase to form a positive sense RNA. For this they make use of their own RNA replicase also called RNA-dependent RNA-polymerase. This helps in the formation of positive RNA template strands through complementary base pairing that is necessary for it's replication. It has been seen in several cases that the RNA-dependent RNA-polymerase(RdRP) switches from a replicase to a transcriptase due to the presence of a complete dsRNA genome in the polymerase complex at completion of replication process that might be inducing this conformational change. Thus, Negative-sense ssRNA viruses requires RNA-dependent RNA-transcriptase enzyme for their replication. So, the answer is:

Option C. RNA-dependent RNA transcriptase.