Cell Structure - Cell Recognition And The Immune System Flashcards
Describe what is meant by an antigen
An antigen is A foreign molecule that stimulates an immune response
They are often proteins or glycoproteins
State which cells and molecules enable the immune system to identity
Pathogens
Abnormal body cells
Toxins
Cells from other individuals in the same species
Describe the process of phagocytosis
- Phagocyte recognises antigen as foreign
- The pathogen is engulfed by the phagocyte
- Engined pathogen is contained inside a vesicle called a phagosome
- Lysosomes fuse with the phagosome and releases lysozymes into the phagosome
- Lysozymes hydrolyse the molecules
Describe the process of the cellular response
- Phagocyte engulfs the pathogen,hydrolyses it and presents the antigen on the surface of its membrane
- Helper t-cell with specific hcomplementary receptor, binds to and is activated
- The activated t-helper cell then releases chemical signals which further activate:
More phagocytes
Cytoxic t-cells which kill infected cells directly
Specific B-cells
Describe the process of the humoral response
- Specific B cells are activated by their specific T helper cell.
- B cells clone into memory cells and plasma cells
- Plasma cells secrete specific antibodies which bind to the foreign pathogen
Define the term monoclonal antibody
Antibodies with the same tertiary structure which are complementary to and bind to one type of antigen and come from the same type of B cell
Explain how antibodies lead to the destruction of pathogens
- When an antibody binds to an antigen it is known as an antigen-antibody complex
- This causes pathogens to lump together (agglutination)
- Many cells can now be engulfed by a phagocyte in one go
Describe the primary immune response
When the antigen infects the body for the first time
Antibodies are produced more slowly
There are less antibodies as it take time for clonal selection
Symptoms occur
Describe the secondary immune response
Produced due to the presence of specific memory B cells
Clonal selection occurs more quickly
Plasma cells produce many more antibodies at a faster rate
The infection is overcome before symptoms can occur
What is a vaccine?
Vaccines contain antigens from the pathogen
Vaccinations make an individual immune to a certain antigen
They create a primary response against an antigen so that memory B cells are formed with complementary antibodies without the symptoms of the pathogen itself
Describe the process by which a vaccine makes a person immune to a pathogen
- Vaccines contain antigens from the pathogen
- A phagocyte engulfs the antigen and presents it on its surface membrane
- A specific helper T cell with a complementary receptor protein binds to the antigen
- This helper T cell stimulates a specific B cell which divides by mitosis
- B cells clone into plasma cells which produce + secrete many antibodies
- The antibodies agglutinate the antigen and destroy it
- Memory B cells are produced so on a second exposure to the antigen, more antibodies are produced more quickly, destroying the pathogen before symptoms are displayed
Describe what herd immunity is and explain how it protects unvaccinated individuals in a population
If a majority of the population are vaccinated then most people cannot get the disease
Therefore those who are not vaccinated are also protected as there are less people to transmit the disease
Give 3 ethical issues regarding the use and production of vaccines
- The vaccine may have side effects and the risk and severity of the side effects can vary between vaccines
- Development and testing may involve use of animals
- People may be forced to have vaccines even if they do not agree with them
Describe what antigenic variability is and how it arises
Due to mutations in pathogen DNA, tertiary structure of antigen protein can change shape
In a second exposure, the antigen binding site of antibodies from the memory cells will not be complementary and a second response does not occur
Explain how antigenic variability reduces the effectiveness of vaccines
Vaccines become ineffective as antibodies produced as a result of the vaccine are no longer complementary
A new vaccine needs to be made each time the antigen changes which take time and is expensive
Contrast the differences between active and passive immunity
Active immunity:
- following exposure to an antigen, specific memory B cells are made which produce antibodies against antigen
Passive immunity:
- antibodies against the antigen are put straight into the body, the immune system does not make the antibodies
State the advantages of active immunity
Immunity is longer lasting
State the disadvantages of active immunity
- Take more time to make memory cells and become immune
- In natural active immunity you will get symptoms of the disease
- In artificial active immunity you can only administer the vaccine before getting the disease
State the advantages of passive immunity
- Can be given after exposure to antigen / pathogen
- Works straight away
State the disadvantages of passive immunity
- Short term as antibodies become broken down
- Short term as no memory cells are produced
Describe one use of monoclonal antibodies in treating disease
Treating cancer:
- monoclonal antibodies which have anti-cancer drug can be made complementary to the cancer cell antigen
- monoclonal antibodies bind only to cancer cells + kill them
- fewer healthy cells are damaged
Describe one use of monoclonal antibodies in diagnosing disease
Pregnancy tests:
- test strip contains hCG monoclonal antibody with a coloured dye attached
- urine flows along test strip and any hCG binds to monoclonal antibody
-hCG- antibody complexes with dye bind to fixed hCG antibody and build up on test line causing a coloured band to appear
- if no hCG present then antibodies flow to control line
- colour of test line changes confirming test worked correctly and is a negative result
Describe the stages involved in the ELISA test
- The antigen is bound to the bottom of a plastic well
- Sample is added + if antigen is present then it binds to antigen
- The well is washed to remove any unbound antibody
4.2nd antibody complementary to 1st is added and it has an enzyme attached to it - The well is washed again to remove unbound 2nd antibody
- Solution containing substrate is added
- Enzyme on 2nd antibody reacts to substrate, producing a colour change which is a positive result for the presence of antibody
Explain how HIV infects and replicates in helper t-cells
- The attachment protein on HIV binds to a complementary receptor on the helper T-cell
- The capsid enters the cell and releases the RNA into the cytoplasm
- Reverse transcriptase makes DNA from the HIV RNA
- Using the host cell’s enzymes and ribosomes for protein synthesis, viral proteins are made from the DNA
- New virus particles are formed from the proteins which bud from the cell and infect more helper T-cells
Explain how HIV causes AIDS
- HIV kills helper T-cells
- When helper T- cell numbers become low, the immune system starts to fail and serious infections can kill the patient
Why do antibiotics not kill viruses?
Antibiotics target parts of bacteria which are not found in a virus
Viruses are hard to kill because they replicate inside cells and have few drug targets
