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2.6Cell Structure

Vaccines, Disease and Monoclonal Antibodies — AQA A Level Biology 7402 Revision Notes & Topical Questions

5 min read 12 parts Lesson 36 of 47 Unit quiz

📚 AQA A Level Biology 7402 Hub / Topical Revision
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Lesson summary

Vaccines, Immunity Types and HIV — AQA A LEVEL BIOLOGY 7402 notes: Explain how vaccines give protection, distinguish active and passive immunity, and describe HIV infection.Vaccines introduce pathogen antigens (or genetic material that codes for the antigens) into the body.

  • Herd immunity
  • reverse transcriptase
  • retrovirus
  • Worked example 1
  • Worked example 2
  • Worked example 3

Section 1 of 12Vaccines and herd immunity

Vaccines introduce pathogen antigens (or genetic material that codes for the antigens) into the body. This triggers a specific immune response in which T helper cells activate plasma cells to release antibodies and memory cells are produced, giving a faster and stronger secondary response. Vaccination produces active immunity.

Herd immunity occurs when enough people are vaccinated to stop the spread of infection. It reduces the number of susceptible individuals, so unvaccinated people (such as babies or those with weakened immune systems) are protected. The more infectious a disease, the higher the proportion of the population that must be vaccinated.

Section 2 of 12Active and passive immunity

Active immunityPassive immunity
SourceBody produces its own antibodies after stimulation by antigensAntibodies received from another organism
Memory cellsPresentAbsent
DurationLong termShort term
NaturalExposure to a pathogen (infection)Antibodies passed via the placenta or colostrum/breast milk
ArtificialVaccinationAntibodies manufactured and injected or transfused (e.g. monoclonal antibodies)

In active immunity the body produces the antibodies, whereas in passive immunity the body is given them.

Section 3 of 12HIV structure and replication

HIV (human immunodeficiency virus) has an RNA genome, a capsid, a lipid envelope with attachment proteins, and the enzyme reverse transcriptase. It is a retrovirus: its genetic material is RNA rather than DNA, and reverse transcriptase converts RNA into DNA, which can then be transcribed by the host cell. The steps are:

1
Viral RNA enters the cell.
2
Viral reverse transcriptase produces a DNA copy of the viral RNA.
3
The DNA copy is inserted into the chromosomes of the cell.
4
Each time the cell divides it copies the viral DNA, and new virus particles are made.

Section 4 of 12HIV infection and AIDS

HIV infects helper T cells, damaging the immune system.

1
Initial infection often causes mild flu-like symptoms, followed by a latent period with no obvious symptoms.
2
As helper T cells decline, B cell activation, antibody production and phagocytosis are reduced.
3
When the immune system can no longer respond to pathogens the person develops AIDS.
4
Opportunistic infections (for example TB) can then occur and can be fatal.
5
There is currently no cure, but antiviral drugs can slow virus replication.

Section 5 of 12Worked examples

  1. Explain how vaccination protects against infection. [4]4 marks

  2. Explain why herd immunity protects unvaccinated people. [2]2 marks

  3. Explain why HIV leads to weakened immunity. [3]3 marks

Section 6 of 12Monoclonal antibodies

Monoclonal antibodies (mAbs) are identical antibodies produced from a single B cell clone.

They are highly specific and bind to one particular antigen.
Targeting medication
Uses include targeting medication (drug delivery),
  • where a drug is attached to an antibody that binds to antigens on cancer cells so the drug reaches the target cells,
  • and diagnosis, for example in the pregnancy test and in tests for HIV.
You must be able to explain why mAbs are specific, how they are used in drug targeting, and give examples of diagnostic uses.
You are not expected to know how they are produced.

Section 7 of 12ELISA

ELISA (Enzyme-Linked Immunosorbent Assay) uses antibodies to detect the presence and quantity of a specific antigen or antibody in a sample such as blood plasma.

ELISA
An antibody linked to an enzyme binds to the target; when substrate is added, the enzyme catalyses a reaction forming a coloured product,
  • so the solution changes colour.
If there is a colour change, the antigen or antibody of interest is present.
An indirect ELISA test can be used to test whether a patient has antibodies to HIV: patient plasma is added to wells coated with HIV antigen; if antibodies are present they bind; a second enzyme-linked antibody binds to them; washing removes unbound material and the substrate gives a colour.

Section 8 of 12Ethical issues

1
Vaccines are first tested on animals, which some view as unethical.
2
Clinical trials raise questions of consent and risk.
3
Some people object to compulsory vaccination, and there is a balance between individual choice and herd immunity.
4
Monoclonal antibody treatments are often expensive, raising concerns about fair access, especially in lower-income countries or health systems.

Be ready to outline ethical issues, particularly animal welfare, consent and access to treatment.

Section 9 of 12Evaluating studies: MMR and autism

In 2005 a study examined the incidence of autism in 30 000 children in Yokohama, Japan between 1988 and 1996. The MMR vaccine was introduced in 1989 and stopped being given in 1993. The number of children diagnosed with autism by age 7 per 10 000 continued to increase even after the vaccine stopped, so the data do not support a link between the vaccine and autism.

When evaluating the methods or results, consider repeatability (enough repeats; same person getting similar results), reproducibility (others getting similar results with the same method) and validity (does the data answer the question and were variables controlled), plus sample size and possible bias.

Section 10 of 12Worked examples

  1. Explain why monoclonal antibodies can be used to deliver a drug to cancer cells. [3]3 marks

  2. Explain the colour change in an ELISA test. [2]2 marks

  3. Evaluate the Yokohama study as evidence that MMR does not cause autism. [3]3 marks

Section 11 of 12Key terms

TermMeaning
VaccinePreparation containing antigens that stimulates immunity
Herd immunityProtection of a population when enough people are immune
Active immunityImmunity from making your own antibodies
Passive immunityImmunity from receiving antibodies
RetrovirusVirus with an RNA genome that uses reverse transcriptase
Reverse transcriptaseEnzyme that makes DNA from an RNA template
TermMeaning
Monoclonal antibodyIdentical antibody from a single B-cell clone
ELISAEnzyme-linked immunosorbent assay
RepeatabilitySame person getting similar results again
ReproducibilityDifferent scientists getting similar results
ValidityWhether data answer the question and variables are controlled

Section 12 of 12Exam technique

1
Saying vaccines contain antibodies - they contain antigens (passive immunity uses antibodies).
2
Confusing HIV with AIDS - AIDS is the later stage.
3
Saying passive immunity gives memory cells.
4
Forgetting to name the cells (plasma and memory) in the answer.
Avoid these mistakes
Thinking monoclonal antibodies are produced by many different B cells - they come from one clone.
Calling ELISA a test for the antibody only - it can detect antigens or antibodies.
Giving ethical points without specifying who is affected.

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