RetrovirusHIV StructureHelper T Cells Mechanism of infection

HIV

Retrovirus: Any group of RNA viruses which insert a copy of their genome into the DNA of the host cell in order to replicate.

BECAUSE they contain only RNA but they don’t contain DNA.

Retroviruses are unable to replicate outside of living host cells !!

HIV Structure: # HIV is an enveloped RNA virus. It acquires an outer envelope consisting of a lipid bilayer with spikes of glycoproteins gp41 and gp120.# Inside this envelope is a nucleocapsid, which surrounds a central core of protein. # Within this core, are two copies of single-stranded RNA (the virus genome). # Proteins and multiple molecules of the enzyme (Reverse transcriptase, Integrase, Ribonuclease H and Protease) also found in the core.

They strengthen the immune system response to infection by:

① Releasing chemicals that attract other white blood cells to the site of infection to attack invading bacteria or virus.

② Releasing chemicals that cause other white blood cells to multiply. These new white blood cells create markers called Antibodies which can identify the foreign invaders throughout the body.

Helper T Cells :

The mechanism of HIV infection:1- The virus enters the body then its surface proteins GP120 attach to CD4 and Co-receptors found on helperT Lymphocytes.

GP 120

2- The lipid membrane of the virus combines with the host cell’s membrane , while the viral core enters the host cell.

Viral core

Viral core

GP 120

3- The core uncoats allowing the viral genetic material which is RNA + Enzymes to enter the cytoplasm of the host cell.

4- The viral enzyme Reverse transcriptase copies the RNA into complementary DNA ( cDNA ).

RNA

5- The viral RNA is destroyed by another viral Enzyme called Ribonuclease H.

6- Reverse transcriptase then synthesizes a second DNA strand using the first as a template.

7- The double-stranded viral DNA enters the nucleus with several types of viral proteins including an Enzyme called Integrase.

Integrase

The Viral DNA

Nucleus

8- Integrase Enzymes splice the viral DNA into the host cell’s chromosomal DNA.

*The integrated viral DNA is known as Provirus*

9- The proviral DNA is transcripted into RNA which contains the code to produce the capsid proteins and other proteins needed for the viral assembly.

Transcripted viral RNA

10- In the spliced form RNA also codes for the envelope proteins ( GP 120 ) and other proteins.

The spliced RNA

*Envelope proteins are produced in the rough endoplasmic reticulum (rER) and then move through The Golgi body before arriving at the cell surface*

Envelope

proteins

11- Finally, viral RNA and associated proteins are packaged and bud off from the host cell surface. These proteins will then bind to the receptors on other immune cells facilitating the spread of infection through the body by destroying more Helper T Cells.

New HIV Cell

*Budding viruses are often exactly like the original particle that initially infected the host. In the case of HIV, however, the resulting viruses display a range of variations which makes treatment difficult*

So , HIV Sequence of Infection is:

1. ATTACHMENTGetting in

2. REVERSE TRANSCRIPTION From viral RNA to DNA

3. INTEGRATION, TRANSCRIPTION a. Viral DNA joins host DNAb. Making multiple viral RNAs

4. TRANSLATION Producing viral proteins

5. VIRAL PROTEASE Cleaving viral proteins

6. ASSEMBLY & BUDDING Getting out