HIV LIFE CYCLE SIMPLIFIED

1. QUESTION: USING MOLECULAR BIAS
DISCUSS THE HIV CYCLE
NAME : MUSONDA MULENGA
REG NO : 18/BSB/BU/R/0003
LECTURER: WINSTON KABISWA
COURSE: MOLECULAR BIOLOGY

2. OBJECTIVES
 INTRODUCTION
 DEFINATION OF HIV AND CYCLE
 SEVEN STAGES OF HIV LIFE CYCLE
 HIV REPLICATION CYCLE
 CONCLUSION
 REFERENCES

3. INTRODUCTION
 The human immunodeficiency virus[HIV] is a lent virus[a subgroup of retrovirus]that
causes HIV infection.
 HIV gradually destroy the immune system by attacking and killing a type of white blood
cell called CD4 cell
 HIV leads to low levels of CD4+ T cells through a number of mechanisms.

5. HIV REPLICATION OR LIFE CYCLE
 Refers to how the HIV virus reproduces using the genetic makeup of the host cell[human cell].
Which begins when HIV fuses with the surface of the host cell. a caspid containing the virus genome and proteins, then
enters the cell.
 The shell of the caspid disintegrates and the HIV protein called reverse transcriptase transcribes the viral RNA into
DNA.

6. CONT…..
 The viral DNA is transported across the nucleus,where the HIV protein integrates the HIV
DNA into the hosts DNA.
 The hosts normal transcription machinery transcribes HIV DNA into multiple copies of
new HIV RNA.
While the cell uses other copies of the RNA to make new HIV proteins.

7. CONT……….
 The new viral RNA and HIV proteins move to the surface of the cell.
Where a new ,immature HIV forms.
 Finally the virus is released from the cell,and the HIV Protein called protease cleaves newly synthesized polyproteins
to create a mature infectious virus.

9. SEVEN STAGES OF HIV CYCLE
1. Viral attachment
2. Binding and fusing
3. Viral uncoating
4. Transcription and translation
5. Integration
6. Assembly
7. Maturation and budding

11. Viral Attachment
 Once HIV enters the body (typically through sexual contact, blood exposure, or mother-to-child transmission), it
seeks out a host cell in order to reproduce. The host in the case is the CD4 T-cell used to signal an immune defense.
 In order to infect the cell, HIV must attach itself by way of a lock-and-key type system. The keys are proteins on the
surface of HIV which attach to a complimentary protein on the CD4 cell much in the way a key fits into a lock. This
is what is known as viral attachment.

12. Binding and Fusion
 Once attached to the cell, HIV injects proteins of its own into the cellular fluids (cytoplasm) of the T-cell. This
causes a fusion of the cell membrane to the outer envelope of the HIV virion. This is the stage know as viral fusion.
Once fused, the virus is able to enter the cell.

13. Viral Uncoating
 HIV uses its genetic material (RNA) to reproduce by hijacking the genetic machine of the host cell. In doing so, it can
churn out multiple copies of itself. The process, called viral uncoating, requires that the protective coating
surrounding the RNA must be dissolved. Without this step, the conversion of RNA to DNA (the building blocks for a
new virus) cannot take place.

14. Transcription and Translation
 Once in the cell, the single-stranded RNA of HIV must be converted to the double-stranded DNA. It accomplishes
this with the help of the enzyme called reverse transcriptase.
 Reverse transcriptase uses building blocks from the T-cell to literally transcribe the genetic material in reverse: from
RNA to DNA. Once converted DNA, the genetic machine has the coding needed to enable viral replication.

16. Integration
 In order for HIV to hijack the host cell's genetic machinery, it must integrate the newly formed DNA into the nucleus
of the cell. Drugs called integrase inhibitors are highly capable of blocking the integration stage by blocking the
integrase enzyme used to transfer the genetic material.

17. Assembly
 Once integration has occurred, HIV must manufacture protein building blocks that it uses to assemble new virus. It
does so with the protease enzyme, which chops protein into smaller bits and then assembles the pieces into new, fully
formed HIV virions. A class of drugs called protease inhibitors can effectively block the assembly process.

18. Maturation and Budding
 One the virions are assembled, they go through the final stage in which the mature virions literally buds from the
infected host cell. Once released into free circulation, these virions go on to infect other host cell and begin the
replication cycle yet again.
 There are no drugs that can prevent the maturation and budding process.
 The average life span of virus-producing host cells is short, around two days. Each infected cell can produce an
average of 250 new HIV virions by before it fails and dies.

20. references
UNAIDS/WHO policy statement on HIV testing(PDF)5th October 2006.
JM Appel (June 2006)
Weiss RA (May 1993)
Kumar, vinay (2012)
HIV Latency(2011
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