Virus tutorial - Essay question 2 (HIV structure/function)

1.    The viral genome of HIV consists of two linear (+) single-stranded RNA, which carries the genetic information of the virus. [1]

2.    It has an cone-shaped capsid made up of capsid proteins/capsomeres to protect the viral genome and enclose two reverse transcriptase molecules, HIV protease and integrase. [1]

      (***Note: some diagrams of HIV are wrong. All 3 TYPES of enzymes are enclosed within the capsid protein.)

       (***Note: contrary to pictures of HIV, there are actually more than 1 protease and 1 integrase in each capsid so don't say that there is 1 only. To be safe, just exclude the numbers in your answer when you are talking about protease and integrase.)

3.    The viral nucleocapsid is surrounded by an envelope derived from the surface membrane of the host cell. There are glycoprotein spikes, gp 120 and gp41, embedded in the envelope. [1]

4. gp120 binds specifically to a complementary cell surface receptor protein CD4 on the surface of a T lymphocyte. gp41 helps in the fusion between the viral envelope with the host cell membrane.    

 

5.    Entry of the virus into the host cell occurs through fusion of the viral envelope with the host cell membrane, or receptor-mediated endocytosis (RME). [1]

6.    The internalised viral capsids are readily digested and removed by host cellular enzymes to release the viral (-) single-stranded RNA and viral enzymes (eg. reverse transcriptase and integrase).

7.    In the cytoplasm, the released reverse transcriptase (with RNA-dependent DNA polymerase)  uses the (+) single-stranded RNA as a template to synthesize a complementary single-stranded DNA (cDNA) during reverse transcription. Reverse transcriptase (DNA-dependent DNA polymerase) also subsequently converts cDNA to a linear double-stranded DNA. [1]

     (***Note: it is ok not to mention the type of polymerase as REVERSE TRANSCRIPTASE is the keyword/marking point).

8.    The double-stranded viral DNA migrates to the nucleus of the host cell and and is integrated into the the host genome by integrase, forming a provirus. [1]

            (***Note: Provirus refers to the integrated phage genome only, and does not include the bacterial host genome.)

9.    When the host cells are activated, the integrated provirus is transcribed into viral mRNA molecules within host cell nucleus. This viral mRNA serves as new viral genomes and for translation into viral polyproteins in the host cell cytoplasm. [1]

10.    HIV protease then cleaves the viral polyproteins to form functional proteins (capsid proteins, viral envelope glycoproteins, and viral enzymes - protease/reverse transcriptase/integrase). [1]