Lecture 2 HIV
General global distribution of HIV infections.
Epidemics not confined to one specific place in the world so it becomes a Pandemic = HIV virus
is an example of a pandemic
General temporal trends in HIV infection rates.
Not proportionate around the world though
The impact of this disease isn’t felt equally or uniformly around the world
Prevalence Adults with HIV + , mostly the sub-saharan Africa, (south Africa etc) and Russia
43 years old on average to live before they die
60% of the infected hiv people are living in sub-saharan Africa
90% + of <15 year old children living with HIV are located in Sub-saharan Africa
People with HIV is gradually increasing over time
Factors that explain why no cure or universal vaccine has been developed for HIV/AIDS.
Constantly changing continues to evolve over time so even if we do find some kind of
cure right now it may not work anymore over time.
Conspiracy theories, maybe it’s because if a cure is developed, many people with the
infection will want to take the cure instead of consistent treatment so the companies that
offer the HIV treatment would lose money because of the developed cure that would only
be needed to be taken once in a person’s lifetime.
Our immune system doesn’t carry any defenses for HIV
There are multiple different strains of HIV because it keeps on changing so a drug or a
vaccine that defends one of these strains may not work for the other types.
Reasons why viruses are not considered “alive”.
Where would viruses fit in the tree of life? NO WHERE… but why?
Because viruses are not ALIVE!
They cannot self-reproduce, they can reproduce but in order to do so they need a host
(parasites), they don’t have their own metabolic processes because they are not formed by
Being cell-based/cellular is a necessity to be considered as alive.
Viruses are not cells, they’re much smaller than cells
Reasons why anti-viral drug therapies often have serious side effects.
In order for a virus to reproduce, they have to get into a cell/host cell to reproduce.
They use the host’s cells metabolism to reproduce
So if an anti-viral drug is taken, we can’t inhibit the virus without also killing the host
This is because the virus is using the host cells machinery/metabolic processes, and so by
taking the anti-viral drugs to kill the virus, damage will occur to the host cells that are
infected with the virus which will result in some serious side effects. Doctors don’t recommend or prescribe these anti-viral drugs very often, because they
cause serious side effects (collateral damage)
Major steps in life cycle of HIV.
Retroviruses unlike every cell-based life, retroviruses like HIV do not store their
genetic information in the form of DNA, instead it’s stored as RNA.
So, in order to intergrate themselves into the hot cell, it has to go through a step called
Using RNA as a template to synthesize DNA.
No proofreading processes associated with reverse transcription
Reverse transcription has a huge rate of errors, like for example adding a wrong base to
the chain results into mutation, mutation rate in HIV is a million times higher than
mutation rate in humans.
There’s a high mutation rate due to reverse transcriptase
What’s reverse transcriptase? Usually the life cycle of a living cell is synthesized from
the genetic information in the form of DNA. It is transcribed to RNA which is than
translated to protein with the help of ribosomes on the endoplasmic reticulum. As you
can see, this life cycle is uniform, meaning the process cannot go backwards from protein
to synthesize DNA. But the process called “Reverse Transcriptase” is an extra step to the
life cycle. It is used for viruses for example to reproduce, by reverse transcribing their
genetic information which is in the form of RNA to DNA in order to undergo a regular
life cycle. DNARNAProtein. This is the main reason why viruses are not considered
as being living organisms because they can’t self-reproduce. They need a host cell’s
metabolic processes in order to undergo reverse transcriptase and then reproduce.
Difference between Retrovirus and a normal virus
o Retrovirus has to go through reverse transcription in order to obtain DNA and
o Normal virus, most of them, already have their genetic information in the form of
DNA so they can transcribe them to RNA and then translate them to proteins.
Specific role of integrase and reverse transcriptase in retroviral life cycle.
Retroviral life cycle:
Virion = HIV particle, enters the host cell and injects its genome (RNA) and the few
proteins that it has into the host cell.
One of the viral enzymes “reverse transcriptase” reverse transcribes the viral RNA into
Why the viral RNA has to become viral DNA? … Because it needs to be DNA in order to
enter the host’s chromosomes.
Another one of the retrovirus enzymes is “Intergrase” which is a splicing enzyme, inside
the nucleus of the host the viral DNA gets inserted into the host’s genome/chromosome
At that point, the hosts cell physiology is hijacked, the viral DNA is transcribed to viral
RNA and then translated into viral protein which are new virions assemble at the surface
of the host cell, they bud off or lyse (exit the host cell by killing it) to infect other host
cells. Takes down the hosts immune system by replicating itself, and if the virus doesn’t kill the
host cell as it exits, the infected host immune cells will be recognized by other immune
cells and taken down that way.