topic 2 - HIV and viruses Flashcards
cgp (topic 2C) 54 - 55
what does HIV stand for
human immunodeficiency virus
what does HIV lead to
acquired immune deficiency syndrome - AIDS
what is HIV
a virus which can weaken a person’s immune system by destroying helper t cells
what cells do HIV target
helper t-cells - which act as host cells for the virus
why does HIV effect the immune system so badly
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
when do people infected with HIV develop AIDS
when the helper t-cell numbers in their body reach a critically low level
name four structures of HIV
(1) attachment proteins
(2) capsid
(3) envelope
(4) reverse transcriptase
what does the HIV core contain
the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase - which is needed for virus replication)
what is the HIV envelope and what’s it made out of
an extra outer layer - made of membrane stolen from the cell membrane of a previous host cell
what sticks out of the HIV envelope
loads of copies of an attachment position that help HIV attach to the host helper t-cell
where does HIV reproduce
inside the cells of the organism it has infected - HIV replicated inside the helper t-cells of the host
why does HIV use host cells
it doesn’t have the equipment (such a enzymes and ribosomes) to replicate on its own - so it used those of the host cells
what’s the first step of how HIV replicates
the attachment protein attaches to a receptor molecule on the cell membrane of the host helper t-cells
what’s the second step of how HIV replicates
the capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm
what’s the third step of how HIV replicates
inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
what’s the fourth step of how HIV replicates
from this, double stranded DNA is made and inserted into the human DNA
what’s the fifth step of how HIV replicates
host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
what’s the sixth step of how HIV replicates
the viral proteins are assembled into new viruses, which bud from the cell and go to infect other cells
when are people with HIV classed as having AIDS
when symptoms of their failing immune system start to appear or their helper t-cell count drops below a certain level
how long is the length of time between infection with HIV and the development of AIDS
it varies between individuals but without treatment it’s usually around 10 years
what are the initial symptoms of AIDS
minor infections of mucous membranes (e.g the inside of the nose, ears and genitals) and recurring respiratory infections
what happens as AIDS progresses
the number of immune system cells decreases further - patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis
what happens during the last stages of AIDS
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
what are factors that affect progression of HIV and AIDS and survival time with AIDS
existing infections, the strain of HIV they’re infected with, age and access to healthcare
why don’t antibiotics work against viruses
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
what are most antiviral drugs designed to target
the few virus specific enzymes (enzymes that only the virus uses) that exist
how are antiviral drugs designed to target HIV
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
what is the antiviral drug for HIV called
reverse-transcriptase inhibitors
is there a cure for HIV
no but antiviral drugs can be used to slow down the progression of HIV infection and AIDS in an infected person
what is the best way to control HIV infection in a population
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
