topic 2 - HIV and viruses

Question 1

what does HIV stand for

Answer 1

human immunodeficiency virus

Question 2

what does HIV lead to

Answer 2

acquired immune deficiency syndrome - AIDS

Question 3

what is HIV

Answer 3

a virus which can weaken a person’s immune system by destroying helper t cells

Question 4

what cells do HIV target

Answer 4

helper t-cells - which act as host cells for the virus

Question 5

why does HIV effect the immune system so badly

Answer 5

helper t-cells send chemical signals that activate phagocytes, cytotoxic t-cells and b-cells so they’re very important in the immune system - without helper t-cells the immune system is unable to mount an effective response to infections because other immune system cells don’t behave how they should

Question 6

when do people infected with HIV develop AIDS

Answer 6

when the helper t-cell numbers in their body reach a critically low level

Question 7

name four structures of HIV

Answer 7

(1) attachment proteins
(2) capsid
(3) envelope
(4) reverse transcriptase

Question 8

what does the HIV core contain

Answer 8

the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase - which is needed for virus replication)

Question 9

what is the HIV envelope and what’s it made out of

Answer 9

an extra outer layer - made of membrane stolen from the cell membrane of a previous host cell

Question 10

what sticks out of the HIV envelope

Answer 10

loads of copies of an attachment position that help HIV attach to the host helper t-cell

Question 11

where does HIV reproduce

Answer 11

inside the cells of the organism it has infected - HIV replicated inside the helper t-cells of the host

Question 12

why does HIV use host cells

Answer 12

it doesn’t have the equipment (such a enzymes and ribosomes) to replicate on its own - so it used those of the host cells

Question 13

what’s the first step of how HIV replicates

Answer 13

the attachment protein attaches to a receptor molecule on the cell membrane of the host helper t-cells

Question 14

what’s the second step of how HIV replicates

Answer 14

the capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm

Question 15

what’s the third step of how HIV replicates

Answer 15

inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template

Question 16

what’s the fourth step of how HIV replicates

Answer 16

from this, double stranded DNA is made and inserted into the human DNA

Question 17

what’s the fifth step of how HIV replicates

Answer 17

host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA

Question 18

what’s the sixth step of how HIV replicates

Answer 18

the viral proteins are assembled into new viruses, which bud from the cell and go to infect other cells

Question 19

when are people with HIV classed as having AIDS

Answer 19

when symptoms of their failing immune system start to appear or their helper t-cell count drops below a certain level

Question 20

how long is the length of time between infection with HIV and the development of AIDS

Answer 20

it varies between individuals but without treatment it’s usually around 10 years

Question 21

what are the initial symptoms of AIDS

Answer 21

minor infections of mucous membranes (e.g the inside of the nose, ears and genitals) and recurring respiratory infections

Question 22

what happens as AIDS progresses

Answer 22

the number of immune system cells decreases further - patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis

Question 23

what happens during the last stages of AIDS

Answer 23

patients have very low number of immune system cells and can develop a range of serious infections such as toxoplasmosis of the brain (a parasite infection) and candidiasis of the respiratory system (fungal infection) - it’s these serious infections that kill AIDS patients, not HIV itself

Question 24

what are factors that affect progression of HIV and AIDS and survival time with AIDS

Answer 24

existing infections, the strain of HIV they’re infected with, age and access to healthcare

Question 25

why don’t antibiotics work against viruses

Answer 25

antibiotics kill bacteria by interfering with their metabolic reactions - they target the bacteria enzymes and ribosomes used in these reactions - bacterial enzymes / ribosomes are different from human enzymes / ribosomes - antibiotics are designed to only target the bacteria ones so they don’t damage human cells
viruses don’t have their own enzymes/ ribosomes - they use the ones in the host’s cells - as human viruses use human enzymes / ribosomes to replicate, antibiotics can’t inhibit them as they don’t target human processes

Question 26

what are most antiviral drugs designed to target

Answer 26

the few virus specific enzymes (enzymes that only the virus uses) that exist

Question 27

how are antiviral drugs designed to target HIV

Answer 27

HIV uses reverse transcriptase to replicate - human cells don’t use this enzyme so drugs can be designed to inhibit it right affecting the host cell

Question 28

what is the antiviral drug for HIV called

Answer 28

reverse-transcriptase inhibitors

Question 29

is there a cure for HIV

Answer 29

no but antiviral drugs can be used to slow down the progression of HIV infection and AIDS in an infected person

Question 30

what is the best way to control HIV infection in a population

Answer 30

by reducing its spread - HIV can be spread via unprotected sexual intercourse, through infected bodily fluids and from a HIV positive mother to her foetus - not all babies from HIV postitive mothers are born infected with HIV - taking antiviral drugs during pregnancy can reduce the chance of the baby being HIV positive