HIV

Question 1

What is the structure of HIV?

Answer 1

• Lipid envelope = extra outer layer made up of membrane taken from host cell membrane
• Attachment proteins = embedded in envelope, complementary to recepor proteins on the membrane of T cells
• Capsid = outer protein coat enclosing 2 single strands of RNA and enzymes needed for viral replication

Question 2

Where does HIV replication occur?

Answer 2

inside the helper T cells of the host as it cannot replicate on its own

Question 3

What is the process of HIV replication?

Answer 3

1.) HIV is transported around in the blood until the attachment proteins on the HIV attaches to a CD4 receptor on the cell membrane of the host helper T cell
2.) the HIV protein capsid fuses with the helper T cell membrane allowing the genetic material (RNA) and enzymes to enter the cell into the cytoplasm
3.) the HIV enzyme reverse transcriptase makes a DNA copy of the viral RNA genome
4.) the DNA copy is then inserted into the host cells DNA and when the cell reproduces, it manufactures the genome of the HIV virus including the RNA genome which passes out of nuclear pores which is used by the cells ribosomes to assemble HIV protein coat
5.) the viral proteins are assembled to form a bud which breaks off to become a new HIV virus which is surrounded by the host cell membrane

Question 4

How does HIV cause symptoms of AIDS?

Answer 4

• when the virus replicates in the helper T cells it effects the normal functioning immune system
• the virus kills the cell as they leave and infect T helper cells can be killed by killer T cells
• this reduces the T helper cells available which means they cannot activate the correct B cell which leaves the person vulnerable to disease/ cancer

Question 5

Why do antibiotics not work with viruses?

Answer 5

• viruses replicate inisde of cells making it hard to destroy them without harming host cells
• antibiotics kill bacteria by interfering with their metabolic reactions by targeting the bacterial enzymes and ribosomes used in these reactions - these are different from human enzymes and ribosomes so antibiotics are designed to only target to bacterial ones so they don’t harm human ones
  –> viruses have different mechanisms to replicate and no cell so wall so it cant be destroyed by antibiotics and rely on host cells to carry out metabolic activity as they lack their own metabolic pathway and organelles (enzymes and ribosomes)
• antiviral drugs are deigned to target few virus specific enzymes
• viruses are in host cell the majority if the time so antibiotics cant get to the virus to have an effect

Question 6

How can we control HIV infection?

Answer 6

• protected sexual intercourse
• not sharing infected bodily fluids e.g. not sharing needles
• taking antiviral drugs during pregnancy to resduce chance of baby being HIV positive (if mother is HIV positive)