[Unit 5.7] | The Human Immunideficiency Virus (HIV)

Question 1

Describe the structure of HIV.

Answer 1

• Lipid envelope
• With attachment proteins embedded in it

• Capsid
• Containing RNA & Reverse Transcriptase

Question 2

What is the role of reverse transcriptase?

Answer 2

Uses RNA to create DNA.

Question 3

Describe the process of HIV replication.

Answer 3

1. Attachment proteins bind to a receptor on the surface of a helper T cell.
2. Capsid fuses with the membrane and releases RNA and reverse transcriptase into the cell.
3. Reverse transcriptase creates a single-stranded DNA molecule that complements its RNA template
4. It then converts it into a double stranded molecule before inserting it into the host’s nucleus.
5. Ribosomes and enzymes are used to create copies of viral proteins and the viral genome.
6. Viral proteins & genomes are assembled to form new virions.

Question 4

Describe the progression of AIDS symptoms.

Answer 4

• Initial severe flu-like symptoms.

• Long latency period (up to 10 years).

• Low helper T cell count in blood.

• Immune system produces a weakened response against pathogens that most people would be immune to.

Question 5

What does ELISA mean?

Answer 5

Enzyme-Linked Immunosorbent Assay

Question 6

Define immunosorbent.

Answer 6

• Denoting techniques that involve the absorption of antibodies by insoluble preparations of antigens.

Question 7

How can ELISA be used?

Answer 7

• Medical Diagnosis
• Research Purposes
• Detection of molecules complementary to antibodies
• To determine the quantity of antigens in a sample

Question 8

What is the difference between direct and indirect ELISA?

Answer 8

• Direct uses one type of antibody, indirect may use multiple.

• Both yield a colour change, but indirect can yield different intensities based on the amount of antigen present.

Question 9

Describe the process of a (direct) ELISA test.

Answer 9

1. Apply antigen sample to a surface & wash off excess.
2. Add antibody (with enzymes attached) & wash to remove excess unbound antibodies.
3. Add the colourless enzyme substrate and observe a coloured product forming if any antibodies have bound to antigens.

(In indirect, the first antibodies do not have enzymes. The antibodies that bind to the first have enzymes attached.)