HIV and the ELISA test

Question 1

What does HIV stand for?

Answer 1

human immunodeficiency virus

Question 2

What does AIDS stand for?

Answer 2

acquired immune deficiency syndrome

Question 3

Explain the relationship between HIV and AIDS

Answer 3

HIV stops your immune system from working properly which means your body can longer defend itself, which is called AIDS

Question 4

What are body fluids with high concentrations of HIV?

Answer 4

blood
semen
vaginal fluids
breast milk
pus from sores

Question 5

What are body fluids with low concentrations of HIV?

Answer 5

sweat
tears
urine
saliva

Question 6

Why is HIV called a retrovirus?

Answer 6

it’s genetic material is RNA

Question 7

Describe the structure of HIV

Answer 7

on the outside there is a lipid envelope with attachment proteins embedded in it
inside there is a protein capsid that encloses two single strands of RNA and enzymes called reverse transcriptase

Question 8

How does HIV replicate?

Answer 8

-the attachment protein attaches to a receptor molecule on the cell membrane of the host helper T cell
-the capsid is released into the cell where it uncoats and releases the genetic material into the cell’s cytoplasm
-inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral DNA template
-from this the double stranded DNA is made and inserted into the human DNA
-host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
-the viral proteins are assembled into new viruses, which bud from the cell and go onto infect other cells

Question 9

Why is there no vaccination for HIV?

Answer 9

HIV genome is very variable

Question 10

What does ELISA stand for?

Answer 10

enzyme linked immunosorbent assay

Question 11

What do antiretroviral drugs do for a patient after they already have HIV?

Answer 11

slow down the replication of the virus by blocking the reverse transcriptase enzyme, slowing the progression of HIV- AIDS

Question 12

What is AIDS?

Answer 12

lots of infections due to a lack of T helper cells

Question 13

What is the point of an ELISA test?

Answer 13

to see if a patient has:
any antibodies to a specific antigen
OR
any antigens to a specific antibody

Question 14

Why does the solution in an ELISA test change colour if the result is positive?

Answer 14

because an antibody is used with an enzyme attached
then the antibody will bind to the antigen if present, so won’t be washed away
then when the substrate is added, the enzyme-substrate complexes are formed which causes the colour change

Question 15

How can the quantity of an antibody/antigen present be determined from an ELISA test?

Answer 15

by the intensity of the colour change- potentially colorimetry?

Question 16

Explain the steps to an ELISA test, with antigens

Answer 16

-antigens from a patient are bound to the inside of a well in a well plate
-a detection antibody (with an enzyme attached) that is complementary to the antigen of interest is added
-if the correct antigen is present, the antibody will bind to it
-the wells are washed thoroughly to ensure nothing else could trigger a positive response for the colour change
-substrate is added

Question 17

How does an ELISA test work with antibodies?

Answer 17

-an antigen is bound to the bottom of a well in a well plate
-patient sample is added, if the complementary antigen is present it will bind to the antigen
-the well is washed thoroughly to remove any unbound antibodies
-a secondary antibody is added that has an enzyme attached
-well is washed again
-substrate is added

Question 18

How do pregnancy tests work?

Answer 18

pregnant women have the hCG hormone in their urine
hCG binds to mobile monoclonal antibodies with coloured beads attached
the urine moves up the stick via diffusion, and then the hCG binds to the immobilised monoclonal antibodies which concentrates the beads so the strip turns blue

the rest should also bind the control strip to show the test has worked