antigen definition
specific molecules often proteins on the surface of cells that identify them as foreign or self
During the process of phagocytosis, what is the specific role of the lysosome?
to fuse with the phagsosome and release lysozomes to hydrolyse the pathogen
why is cellular response important
-Targets viruses, which hide inside host cells, making them inaccessible to antibodies.
-Forms long-term immunity via memory T-cells.
Clonal expansion
- rapid mitotic dividion of t cells
why is Primary Response slow
The immune system must identify the antigen.
Specific B-cells must be activated and clone themselves (clonal selection and clonal expansion must take place).
Plasma cells produce antibodies, which take time to reach a high concentration.
Symptoms of infection occur as the pathogen spreads before it is eliminated.
After the infection is cleared, memory cells (both B and T memory cells) are produced and remain in the body.
why is secondary response fast
Memory B-cells quickly differentiate into plasma cells and produce antibodies.
Memory T-cells rapidly activate cytotoxic T-cells to destroy infected cells.
More antibodies are produced, and are produced more rapidly. They also remain in the bloodstream for longer.
The pathogen is eliminated before symptoms appear, meaning the person may not even realise they were infected.
what does the graph about primary and secondary response explain
There is very little delay or lag time before antibody production begins.
The antibody concentration increases more quickly.
The antibody concentration rises much higher.
The antibody concentration remains higher for longer.
This is the result of
Memory cells being present following the primary immune response.
what is the structure of antibodies
Antibodies are globular proteins made up of four polypeptide chains: two heavy chains and two light chains.
They have variable regions forming two specific antigen-binding sites.
They have constant regions which consist of very similar amino acid sequences in all antibodies.
Disulfide bonds maintain the antibody’s stable quaternary structure by holding the 4 polypeptide chains together.
Antibodies belong to a group of proteins called immunoglobulins (Ig).
what is agglutination
Antibodies have two antigen binding sites (allowing them to bind to antigens on two different pathogens), clumping pathogens together to make them easier for phagocytes to engulf.
how does vaccination lead to immunity
Vaccines contain antigens from a pathogen, which stimulate the immune system to produce a primary immune response, this is an example of artificial, active immuntiy.
These antigens may be on a dead or weakened pathogen or may just be the isolated antigen.
Live Attenuated Vaccines contain a weakened (attenuated) form of the pathogen that can replicate but does not cause disease. This could lead to infection in immunocompromised individuals.
Inactivated (Killed) Vaccines contain pathogens that have been killed by heat or chemicals but still have intact antigens. This type of vaccine often requires booster vaccines.
Once injected with the antigen, an immune response is triggered.
B-lymphocytes produce plasma cells that secrete antibodies.
Memory cells are produced, providing long-term immunity.
On secondary exposure, memory cells respond quickly and produce antibodies faster, preventing symptoms of disease.
How can vaccines prevent the spread of disease
When vaccinated individuals encounter the same pathogen, their immune system rapidly destroys it.
This reduces the chance of transmission of the pathogen to others.
Some pathogens require a large host population to survive, so reducing the number of susceptible individuals can eradicate diseases (e.g., smallpox).
what is herd immunity
When a large proportion of the population is vaccinated, non-vaccinated individuals are also protected.
The pathogen has fewer hosts, reducing its spread.
This is especially important for individuals who cannot be vaccinated, such as those with compromised immune systems.
Threshold for herd immunity varies between diseases (e.g., measles requires ~95% vaccination coverage).
challenges of antigenic variation
Some pathogens, like influenza and HIV, undergo frequent antigenic variation (changes in surface antigens), this is due to mutations in the genetic material of the pathogen.
This means memory cells from previous infections or vaccinations do not recognise the antigens of new strains.
Annual vaccines are required for diseases with high antigenic variation.
Pathogens like HIV evade the immune system by rapidly mutating.
what is active immunity
The immune system actively produces its own antibodies.
what is passive immunity
Antibodies are introduced from an external source.
Active immunity
Occurs when the immune system produces its own antibodies in response to an antigen.
Active immunity will lead to the production of memory cells.
Natural Active Immunity:
Acquired through infection by a pathogen.
Once recovered, a person has lifelong immunity.
Artificial Active Immunity:
Acquired through vaccination containing weakened or inactive pathogens.
Example: MMR vaccine – Stimulates the immune system to produce memory cells.
Passive immunity
Occurs when antibodies are introduced from an external source, such as pre-made antibodies extracted from human or animal blood, rather than being produced by the body.
Passive immunity does not lead to the production of memory cells.
Natural Passive Immunity:
Antibodies are transferred naturally from mother to baby.
Example: Breast milk contains maternal antibodies that protect the baby from infections.
Artificial Passive Immunity:
Pre-made antibodies are injected to provide immediate protection.
Example: Snake antivenom – Contains antibodies extracted from animals to neutralise venom.
HIv replication cycle - HIV cannot reproduce on its own; it hijacks host T-helper cells to replicate.
HIV’s attachment proteins bind to receptors on T-helper cells.
The viral envelope fuses with the host cell membrane, allowing HIV’s RNA and enzymes to enter the cell.
Reverse transcriptase converts viral RNA into DNA.
This step allows HIV’s genetic material to be inserted into the host cell genome.
Once the DNA is integrated into the host cells DNA, the viral DNA is called a provirus and remains dormant for some time.
When activated, the host cell uses the viral DNA to make new viral RNA.
Ribosomes translate this RNA into viral proteins and enzymes.
New HIV particles are assembled inside the host cell.
The new viruses bud off from the host cell, taking part of its membrane to form a new lipid envelope.
The host T-helper cell is destroyed, weakening the immune system.
impact on hiv for the immune system
HIV gradually reduces the number of T-helper cells.
Fewer T-helper cells = B-cells are not activated.
This compromises the immune response, making the individual vulnerable to infections.
Eventually, AIDS develops, leading to life-threatening infections and cancers.
monalconal antibodies
Monoclonal antibodies are identical antibodies with the same tertiary structure, produced by clones of a single B-lymphocyte.
They are designed to bind to one specific antigen, their antigen binding sites will be complementary to the same antigen.
treatment used form monolconal antibodies
Cancer therapy.
Different cells in the body have different surface antigens.
Cancer cells have antigens called tumour markers that are not found on normal body cells.
Monoclonal antibodies can be made that will bind to the tumour markers.
Anti-cancer drugs (eg. radioactive substances) can also be attached to the monoclonal antibodies.
This is then injected into the patient.
When antibodies come into contact with the cancer cells they will bind to the tumour markers.
This results in the drug accumulating in the body where there are cancer cells.
Therefore, the side effects of an antibody-based drug are lower than other drugs because they accumulate near cancer cells only. They don’t damage normal body cells.
what is the eliza test used for
ELISA is used to detect the presence and concentration of antigens or antibodies in a sample.
It relies on antigen-antibody interactions and an enzyme-linked reaction to produce a colour change, indicating a positive result.
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Carbohydrates25
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Polysaccharides22
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Lipids-trglycerides,phospholipids22
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Carbohydrate and Lipid test13
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Proteins85
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proteins0
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Digestion and Absorbtion16
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Mitosis14
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enxymes11
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nucleic acids31
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Januray mock test5
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Meselson and Stahl Watson and Crik2
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Transcription,Translaton,Slicing5
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immune system23
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Protein Synthesis20
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Gene diversity39
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DNA3
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Exchange surfaces2
