Using a well labeled HIV structure, justify how HIV infection occurs and the biochemical disorders that result from such an infection.
Answers
Explanation:
HIV stands for Human Immunodeficiency Virus, a pathogen that works by attacking the human immune system. It belongs to a class of viruses called retroviruses and more specifically, a subgroup called lentiviruses, or viruses that cause disease slowly. 1
HIV cannot replicate on its own, so in order to make new copies of itself, it must infect cells of the human immune system, called CD4 cells. CD4 cells are white blood cells that play a central role in responding to infections in the body. 2
Over time, CD4 cells are killed by HIV and the body’s ability to recognise and fight some types of infection begins to decline. If HIV is not controlled by treatment, the loss of CD4 cells leads to the development of serious illnesses, or ‘opportunistic infections’. In people with normal CD4 cell levels, these infections would be recognised and cleared by the immune system. 3
Experiencing a collection of these infections is the most advanced stage of HIV, which is when a person is also said to have AIDS (Acquired Immune Deficiency Syndrome). Effective testing and treatment of HIV means that the large majority of people living with HIV do not reach this stage. 4
The structure of HIV
HIV is called a retrovirus because it works in a back-to-front way. Unlike other viruses, retroviruses store their genetic information using RNA instead of DNA, meaning they need to ‘make’ DNA when they enter a human cell in order to make new copies of themselves.
HIV is a spherical virus. The outer shell of the virus is called the envelope and this is covered in spikes of the ‘glycoproteins’ gp120 and gp41, which allow HIV to lock onto the CD4 receptor on CD4 T cells and enter the cell. 5
Diagram illustrating The structure of HIV
Inside the virus envelope is a layer called the matrix. The core of the virus, or nucleus, is held in the capsid, a cone-shaped structure in the centre of the virion. The capsid contains two enzymes essential for HIV replication, the reverse transcriptase and integrase molecules. It also contains two strands of RNA – which hold HIV’s genetic material. 6
HIV’s RNA is made up of nine genes which contain all the instructions to make new viruses. Three of these genes – gag, pol and env – provide the instructions to make proteins that will form new virus particles. For example, env provides the code to make the proteins that form the envelope, or shell, of HIV. gag makes the structural proteins such as the matrix and the capsid, and pol makes the enzymes that are essential for making new viruses.
The other six genes, known as tat, rev, nef, vif, vpr and vpu, provide code to make proteins that control the ability of HIV to infect a cell, produce new copies of virus or release viruses from infected cells.