Biology infection and viruses urgent 😳Watch
Rhinoviruses cause the common cold, in actuality, the common cold is caused by a variety of viruses. The stages in which the cold virus attacks the cells on the inside of a human nose are as follows;
Stage 1: Virus attaches to protein receptor on host cell membrane.
Stage 2: RNA of virus is released in to cell as protein capsid is lost.
Stage 3: RNA read at ribosome forming three enzymes, (D, F and G)
Stage 4: New viruses formed using enzymes D and F
Stage 5: Viruses released as host cell membrane deteriorates as the result of the action of enzyme G
Suggest why the enzymes D and F are required in stage 4?
Firstly, I want to identify what enzymes D, F and G are. Since rhinoviruses are I believe retroviruses (enveloped ssRNA viruses) there will of course be three proteins of significance.
I think that enzyme D is reverse transcriptase, which catalyses the transcription of retrovirus RNA into DNA. It does so by using host nucleotides to converts the viral RNA template to a single stranded DNA molecule, which in turn is reverse transcribed to form double stranded DNA from an RNA template. It reads from 5' to 3' forming complementary DNA.
The enzyme F I believe is a protein of importance called integrase, an enzyme which integrates viral DNA into the host cell, by forming covalent bonds between its DNA and the genetic information (DNA) of the host cell it infects. Integrase travels with the double stranded DNA through a nuclear pore to the nucleus of the host cell to locate the host chromosome to allow the virus to insert itself into the host chromosome.
This is called the provirus stage.
Stage 4 I think is assembly (in terms of the lytic cycle). However, the host cell believes this to be normal DNA so it synthesises RNA via transcription, where the mRNA exits the cell nucleus into the cytoplasm where it undergoes translation to produce new proteins like capsids proteins and the three original viral proteins.
The enzymes D and F are thus required at this stage in order to reverse transcribe the viral RNA into double stranded DNA and to integrate this viral DNA with the host cell DNA to produce new viral proteins.
How does enzyme G catalyse the breakdown of the host cell membrane in stage 5
The third enzyme here, G, is protease. These new viruses are called immature viruses since they are missing their capsid. Consequently, they will bud off from the host cell membrane, the mature viruses will thus have envelopes derived from portions of the host cell membrane. In order to achieve this the enzyme protease catalyses the rate of proteolysis, being the breakdown of proteins into smaller amino acids or polypeptides.
I would really appreciate some help and advice regarding my answers.