What you need to know
- 6.6How HIVHuman immunodeficiency virus: an RNA retrovirus that infects T helper cells and can lead to AIDS. infects human cells, causing symptoms that may result in death.
Infection and consequence, not a treatment plan, test result or personal history. ART and U=U are enrichment, not 6.6 recall. Antibodies and T killer cells are 6B.
By the end, you should be able to…
- State that HIV infects T helper cellA T cell that binds to an antigen-presenting cell and releases cytokines that activate B cells and T killer cells. (CD4A receptor glycoprotein on T helper cells that HIV binds to.).
- Outline RNARibonucleic acid: a single-stranded polynucleotide with ribose and uracil. mRNA, tRNA and rRNA take part in protein synthesis. → DNADeoxyribonucleic acid: a double-stranded polynucleotide that carries the genetic code. by reverse transcriptaseAn enzyme from retroviruses, such as HIV, that makes DNA using RNA as a template. and insertionA mutation in which one or more extra bases are added to the DNA sequence. as a provirusViral DNA, such as HIV DNA, that has been inserted into a host cell’s chromosome..
- Explain death via collapse of specific immunity and opportunistic infectionAn infection that rarely causes disease in healthy people but does when the immune system is weakened, as in AIDS. such as TB.
Build your understanding
A virus that targets the coordinator
HIVHuman immunodeficiency virus: an RNA retrovirus that infects T helper cells and can lead to AIDS. is an enveloped RNARibonucleic acid: a single-stranded polynucleotide with ribose and uracil. mRNA, tRNA and rRNA take part in protein synthesis. virus (6A 1). It infects T helper cellA T cell that binds to an antigen-presenting cell and releases cytokines that activate B cells and T killer cells. lymphocytes, which carry CD4A receptor glycoprotein on T helper cells that HIV binds to. receptors, and can also infect some macrophages. Binding CD4 is the specified-level docking step; you do not need a second receptor name unless a question gives it.
The particle fuses, RNA and reverse transcriptaseAn enzyme from retroviruses, such as HIV, that makes DNA using RNA as a template. enter, and reverse transcriptase copies viral RNA into DNADeoxyribonucleic acid: a double-stranded polynucleotide that carries the genetic code.. integraseA viral enzyme that inserts viral DNA into the host cell’s DNA. inserts that DNA into the host genome as a provirusViral DNA, such as HIV DNA, that has been inserted into a host cell’s chromosome.. That is latencyA period when a virus stays in a host cell without making new viruses or causing symptoms. at the molecular scale: the information can sit there, copied when the cell divides, without a burst of particles every hour.
From infection to AIDS
New particles can later be assembled and bud from the T helper cell, killing or exhausting that cell population. As T helper numbers fall, specific immune responses collapse. AIDS names that late stage: opportunistic infectionAn infection that rarely causes disease in healthy people but does when the immune system is weakened, as in AIDS. and some cancers can then kill, because the coordinators of the immune response are missing. Untreated, that is how 6.6 reaches death.
TB is a named partner infection: latent M. tuberculosis can leave tubercleA mass of infected macrophages and other cells walled off in the lungs in tuberculosis. when T helper control fails. That is why 6A 7 and 6A 8 belong together. Do not write a CD4 numerical threshold as required recall; clinics use counts, the specification uses the cell type and the consequence.
Not a recipe
Antiretroviral therapy can suppress viral load; NIH and HIV.gov describe that as treatment that is not a cure. Those sentences are enrichment so you do not write “HIV always kills quickly”. They are not a prescribing protocol and not a 6.6 list of drug names.
Entry into the body uses 6.7 routes: blood, sexual fluids, punctures. This lesson is what happens after the virus has a T helper cell to infect.
NOT: HIV is not a bacterium caught like TB droplets. AIDS is the late stage of HIV infection, not a different virus.
- HIV can also infect some macrophages
- The provirus is copied when the host cell divides
- TB can reactivate when T helper control fails
- A CD4 count threshold is not required recall
- Treatment that suppresses the virus is enrichment, not a cure and not a drug list
Two traps this diagram blocks
- Do not call AIDS a separate virus.
- Do not omit reverse transcriptase when explaining how HIV becomes a provirus.
From the diagram alone
Question
Describe how HIV infection of T helper cells can lead to death. [4]
Show a model answer
HIV binds CD4, and reverse transcriptase copies its RNA into DNA that is inserted as a provirus. New particles are later produced and T helper numbers fall. Without those cells, specific immune responses collapse, and opportunistic infections can then kill.
| Feature | M. tuberculosis | HIV |
|---|---|---|
| Type | Bacterium | Enveloped RNA virus |
| Cell infected | Macrophage in the lung | T helper (CD4) |
| Persistence | Inside cells / tubercles | Provirus in the genome |
| Path to death | Lost alveolar surface; spread | Lost specific immunity; opportunistic infection |
Make your reasoning visible
Name reverse transcriptase
RNARibonucleic acid: a single-stranded polynucleotide with ribose and uracil. mRNA, tRNA and rRNA take part in protein synthesis. → DNADeoxyribonucleic acid: a double-stranded polynucleotide that carries the genetic code. is the unusual step that lets HIVHuman immunodeficiency virus: an RNA retrovirus that infects T helper cells and can lead to AIDS. insert as DNA.
Death is opportunistic
HIV kills by destroying T helpers, so other organisms (or cancers) can then kill the person.
Key explanations
- New particles can later bud from the cell. T helper cellA T cell that binds to an antigen-presenting cell and releases cytokines that activate B cells and T killer cells. numbers fall, so cytokine help for B cells and T killers is lost.
- AIDS is that late stage. opportunistic infectionAn infection that rarely causes disease in healthy people but does when the immune system is weakened, as in AIDS., including reactivation of TB, and some cancers can then kill.
- HIV is not inhaled like TB, and it is not itself a bacterium.
Avoid this misconception
The claim: HIV is a bacterium you catch like TB droplets, and AIDS is a different virus.
The correction: HIV is a virus. AIDS is the late stage of untreated HIV infection when T helper numbers have collapsed. TB is a separate bacterium that can exploit that collapse.
Put the course of HIV infection in order
HIV infects T helper cells. Order the course of infection, from the virus binding to one cell to the collapse of the immune response.
Order the steps
What to do
- Reorder the cards below: drag a card (on a touch screen, drag its number), tap a card then tap where it goes, or use the ↑ and ↓ arrows at its right.
- Press Check under the cards to mark each one green (right place) or red; the count shows how many are right.
- Stuck? Hint first outlines the first wrong place, then gives a clue, then places that step for you.
- Shuffle mixes the cards again; Start again returns them to the starting order. Keyboard: Space picks up, arrow keys move, Space drops.
Put the course of an untreated HIV infection in order.
0 of 8 in the right place
Antiretroviral drugs slow these steps and most treated people never develop AIDS. The time spent as a provirus varies from months to many years.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Which human cells does HIV infect, and which surface receptor does it bind?
Show suggested answer
T helper cells (and some macrophages), binding CD4.
Practice question
Retrieval and explanation · suggested answer
Describe how HIV genetic information becomes part of a T helper genome.
Show suggested answer
Reverse transcriptase makes DNA from viral RNA; integrase inserts that DNA as a provirus.
Practice question
Retrieval and explanation · suggested answer
Explain how untreated HIV infection can result in death.
Show suggested answer
Destruction of T helper cells collapses specific immunity (AIDS), so opportunistic infections such as TB, or some cancers, can kill the host.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Using 6A 2 language, identify latency in HIV, then say why a later TB infection is a 6.6 consequence rather than a second virus causing AIDS.
Show a hint
Provirus versus opportunistic bacterium.
Explore the reasoning
Latency is the provirus remaining in T helper DNA without constantly making particles. AIDS is the late HIV stage. TB is a bacterium that can reactivate when T helpers are gone; it does not become HIV and it does not redefine AIDS as a TB virus.
Recall this lesson
Lesson recall questions
Question 1 of 5: Name the bacterium that causes tuberculosis and the organ it typically infects first.
TB and HIV infection
Practice question
Retrieval and explanation · suggested answer
Name the bacterium that causes tuberculosis and the organ it typically infects first.
Lesson: 6A 7: Case Studies of Disease: Tuberculosis
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
HIV is the virus; AIDS is a stage
6A · Case Studies of Disease: HIV/AIDSNIH HIVinfo defines HIV as the virus that causes HIV infection and AIDS as the most advanced stage if untreated. Medicines can suppress virus in blood but do…Specification 6.6Read & use the scienceClose article
Why this matters
NIH HIVinfo defines HIV as the virus that causes HIV infection and AIDS as the most advanced stage if untreated. Medicines can suppress virus in blood but do not cure the infection. That distinction stops two errors: treating AIDS as a separate pathogen, and treating 6.6 as a drug list. No one on this site is asked for a test result or a history. A clinical viral-load measurement and a CD4-cell count answer different questions: one concerns virus in blood, the other a key immune-cell population. Neither should be used to infer a stranger’s health from appearance.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 6.6 understand how Mycobacterium tuberculosis and human immunodeficiency virus (HIV) infect human cells, causing symptoms that may result in death
Use the science
Why is “AIDS virus” a sloppy name in a 6.6 answer?
Explore a possible response
AIDS is the late stage of HIV infection. The virus is HIV. Using two names as two organisms hides the T helper mechanism.
Explore the source
Antiretroviral drugs interrupt a life cycle
6A · Case Studies of Disease: HIV/AIDSNIH HIVinfo explains that HIV infects CD4 T cells and uses several intracellular steps to make new viruses. Antiretroviral combinations block different steps, greatly reducing viral multiplication. This…Specification 6.6Read & use the scienceClose article
Why this matters
NIH HIVinfo explains that HIV infects CD4 T cells and uses several intracellular steps to make new viruses. Antiretroviral combinations block different steps, greatly reducing viral multiplication. This is not the science-fiction idea of a drug that simply destroys every viral particle on contact. Lower viral load helps protect immune function, but treatment does not erase every infected cell. A clinical viral-load test and a CD4 count give related but different information. The Unit 4 answer should still explain why loss of T helper cells weakens immune responses; naming a medicine alone does not explain the symptoms.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 6.6 understand how Mycobacterium tuberculosis and human immunodeficiency virus (HIV) infect human cells, causing symptoms that may result in death
Use the science
Why could viral load fall after treatment while the patient still needs ongoing treatment?
Explore a possible response
Replication has been suppressed, but infected reservoir cells can remain; a low blood viral load is not proof of eradication.
Explore the source
- The HIV life cycleNIH HIVinfo