BIOLOGY - CELLS AND THE IMMUNE SYSTEM

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What are antigens?
Molecules (usually proteins) that can generate an immune response when detected by the body
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Where are antigens found?
Usually on the surface of cells, including all body cells.
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What are foreign antigens?
Antigens that aren't normally found in the body. The immune system usually responds to these.
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How do antigens allow the immune system to identify pathogens?
All pathogens have antigens on their surface - these are identified as foreign by immune system cells, whcih repsond to detory them.
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What are pathogens?
Organisms that cause disease e.g bacteria, viruses & fungi.
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How do antigens allow the immune system to identify abnormal body cells?
Cancerous or pathogen-infected cells have abnormal antigens on their surface, which trigger an immune response
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What are toxins?
Poisons. Theyre also molecules, not cells. Some toxins are produced by bacteria. Toxins themselves are antigens, it doesnt have any on its surface
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How do antigens allow the immune system to identify toxins?
The immune system can response to toxins, as well as pathogens that release them
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How do antigens allow the immune system to identify cells from other individuals of the same species?
Cells from another person (through organ transplant or blood transfusion) will have some antigens that are different (foreign) which triggers an immune response - causing rejection of transplanted organs.
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How can you prevent the rejection of transplanted organs?
Drugs are taken to suppress the recipients immune system
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What is a phagocyte?
a type of white blood cell that carries out phagocytosis
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What is phagocytosis?
engulfment of pathogens
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Where are pahogcytes found?
in the blood and in tissues
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Explain phagocytosis? (1)
A ohagocyte recognises the foreign antigens on a pathogen
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Explain phagocytosis? (2)
The cytoplasm of the phagocyte mvoes round the pathogen, engulfing it
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Explain phagocytosis? (3)
The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
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Explain phagocytosis? (4)
A lysosome fuses with the phagocytic vacuole. The lysosomes break down the pathogen
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Explain phagocytosis? (5)
The phagocyte then presents that pathogens antigens - activates other immune system cells. It is acting as an antigen-presenting cell.
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What is a lysosome?
An organelle that contains enzymes called lysozymes
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What is a T-Cell?
A type of white blood cell involved in the immune response. Some types activate B cells and some kill pathogens directly.
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How is a T-cell activated?
It has receptor proteins on its surface that bind to complimentary sntigens presented to it by phagocytes
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Name the different types of T-cells?
Helper T cells (these also activate B-cells. Cytotoxic T cells.
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Explain how helper T-cells respond to antigens?
They release chemical signals that activate and stimulate pahgocytes and cytoxoic T-cells
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Explain how Cytotoxix T-cells respond to antigens?
They kill abnormal and foreign cells.
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What are B-cells?
A type of white blood cell involved in the immune response. They produce antibodies
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What are antibodies?
A protein produced by B cells in response to the presence of a pathogen
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Explain clonal selection?
When the antibody on the surface of a B-cell meets a complimentary shaped antigen, it binds to it. Together with the substances released from helper T-cells acitvates the B-cells.
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What happens when B cells are activated?
They divide into plasma cells
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What do plasma cells do?
They secrete loads of antibodies specific to the antigen
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What are monoclonal antibodies?
An antibody produced from a single group of genetically identical B cells.
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Explain agglutination?
When pathogens become ckumped together - this is because an antibody has two binding sites so can bind to two pathogens at the same time
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Explain how antibody destory pathogens
After agglutination has occured, phagocytes bind to the antibodies and phagocytose many pathogens at once. This causes the destruction of pathogens carrying this antigen in the body
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Explain the general structure of an antibody?
Theyre proteins - made up of chains of amino acids. The specificity of an antibody depends on its variable regions, which from antigen binding sites. each variable region is complimentary to a specific antigen. All antibodies have constant regions
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What is the cellular response?
The T-cells and other immune system cells that they interact with e.g phagocytes, form the cellular response
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What is the humoral response?
B-cells, clonal selection and the production of monoclonal antibodies form the humoral response
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What is the primary response?
When an antigen enters the body for the first time, it activates the immune system
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Why is the primary repsonse slow?
Because there arent many B-cells that can make antibody needed to bind to it.
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Explain the funciton of memory cells in the primary response?
They remember the specific antigen and will recognise it a second time round. They record the specific antibodies needed to bind to the antigen
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What is a memory cell?
A white blood cell that remains in the body & remembers how to respond to infections.
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What is the secondary response?
If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. Clonal selection will happen much faster.
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Explain the role of memory cells in the secondary response?
Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen.
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What is active immunity?
The type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
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What is natural active immunity?
This is when you become immune after catching a disease.
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What is artificical active immunity?
This is when you become immune after youve been given a vaccination containing a harmless dose of an antigen
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What is passive immunity?
The type of immunity you get from being given antibodies made by a different organism - your immune system doesnt produce any antibodies on its own
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What is natural passive immunity?
This is when a baby becomes immune due to the antibodies it recieves from its mother, through the placenta and in breast milk
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What is artifical passive immunity?
This is when you become immune after being injected with antibodies from someone else e.eg if you contract tetanus you can be injected with antibodies against tetanus, collected from blood donations
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What are the main differences between active&passive immunity?
Active requires exposure to an antigen. P does not. In A memory cells are produced, they are not in P. In P protection is immediate, whereas it takes a while in A.
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Explain how protection differs between acitve & passive immunity
In acitve, protection is long term because the antibody is produced in response to the complimentary antigen. In passive the protection is short term because the antibodies given are brokwn down.
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How do vaccine help avoid disease?
Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing the disease. You become immune without getting any symptoms.
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What is herd immunity?
Vaccines protect individuals that have them, and, because they reduce the occurence of the disease, those not vaccinated are less likely to catch the disease (less people to catch it off)
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How can vaccines be adminstered?
Taken orally or injected.
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What are the dsadvantages of oral vaccinations?
It could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood. Sometimes booster vaccines are given later onto make sure that more memory cells are produced.
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Outline one of the ethical issues surrounding the use of vaccines?
All vaccines are tested on animals before being tested on humans - some people disagree with animal testing. Animal based substances may be used to produce a vaccine - some may disagree.
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Outline another ethical issues surrounding the use of vaccines ?
Some people dont want to take the vaccine due to the risk of side effect, they are still protected because of herd immunity - some think this is unfair.
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Outline another ethical issues surrounding the use of vaccines?
If there was an epidemic of a new disease (e.g a new influenza virus) there would be a rush to recieve a vaccine and difficult decisions would have to be made about who would be the first to recieve it.
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What is antigenic variation?
When different antigens are formed due to changes in the gene of a pathogen
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Explain how antigenic variation changes the immune response?
When you're infected for the second time, the memory cells produced from the first infection wont recognise the different antigens. The immune system has to start and carry out a primary response against the new antigens.
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Give examples of some antigens that show antigenic variation?
Influenxa & HIV
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Explain how monoclonal antibodies can be useful for treating illnesses & medical diagnosis?
Antibody binding sites are very specific (unique tertiary structure). You can make monoclonal antibodies that bind to anything you want. e.g. a cell antigen or other substance. and they will bind to this (target) this molecule.
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Explain how monoclonal antibodies can be used in cancer treatment
Cancer cells have antigens (tumour makers) not found on body cells. MA have anti-cancer drugs attached to them. When the MA come into contact wiht cancer cells they will bind to the tumour markers. Drug only accumulates where there are cancer cells.
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What is the ELISA test?
The enzyme-linked immunosorbent assay. It allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody.
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Where can the ELISA test be used?
It can be used in medical diagnosis to test for pathogenic infections, for allergies or anything you can make an antibody for.
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Explain how the ELISA test works?
An antibody is used which has an enzyme attached to it, E can react with a substrate to produce a coloured product. Solution in the reaction vessel changes colour. The colour change demonstrates that the antigen/body is present in the sample.
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What is the DIRECT ELISA?
It uses a single antibody that is complimentary to the antigen you're testing for.
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Explain how a DIRECT ELISA works?
Antigens from a patient sample are bound to the inside of a well in a well plate. A detection antibody (with an enzyme attached to it).
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What is an indirect ELISA?
It is different because it uses two different antibodies
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What are the ethical issues surrounding monoclonal antibody therapy?
Animals are used to produce the cells from which the monoclonal antibodies are produced. Some disagree with the use of animals in this way.
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What is HIV?
Human Immunodeficiency virus - affects the human immune system. It eventually leads to AIDS
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What is AIDS?
Acquired Immune Deficiency Syndrome - a condition where the immune system deterioates and eventually fails
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Explain how HIV acts as a host cell?
It infects and eventually kills T-HELPER cells - they act as host cells for the virus.
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Explain how HIV develops into AIDS?
Without enough HELPER T-CELLS, the immune system is unable to mount an effective response to infections because other immune system cells dont behave how they should. HIV becomes AIDS when the HELPER T-CELL number reach a critically low level.
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Describe the initial infection of HIV?
HIV replicates rapidly (flu - like symptoms). After this, HIV replication drops to a lower level - LATENCY PERIOD. During latency period the infected person wont experince any symptoms.
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Explain the inital symptoms of AIDS?
Minor infections of mucous membranes (inside of the nose,ears & genitals) and recurring respiratory infections.
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Explain the later symptoms of AIDS?
As aids progresses the patinet becomes susceptible to more serious infections (chronic diarrhoea, tb). During later stages patients can develop a range of serious infections (toxoplasmosis of the brain) These infections are what kill aids patients.
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Explain the structure of HIV?
Spherical structure, Has a core of RNA and proteins. Outer coating of protein (caspid). Has an envelope - made of previous host cell membrane. Sticking out are attachment proteins - help HIV attach to the host helper T-cell.
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Give an example of a protien in the core of HIV?
Reverse transcriptase - this is needed for virus replication.
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Explain how antibiotics work?
They kill bacteria by interfering with their metabolic reactions. They target bacterial enzymes used in these reactions. They are designed to only target bacterial enzymes & ribosomes, not human ones.
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Explain why antibiotics cant treat viruses?
As viruses dont have their own enzymes and ribosomes (they use host cell ones). Antibiotics only target bacterial processes, not human ones.
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Explain how antiviral drugs work?
They are designed to target the few virus-specific enzymes that exist.
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Explain how HIV can be spread?
Through unprotected sexual intercourse, through infected bodily fluids (blood sharing from contaminated needles) and from a HIV +VE mother to her foetus.
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Card 2

Front

Where are antigens found?

Back

Usually on the surface of cells, including all body cells.

Card 3

Front

What are foreign antigens?

Back

Preview of the front of card 3

Card 4

Front

How do antigens allow the immune system to identify pathogens?

Back

Preview of the front of card 4

Card 5

Front

What are pathogens?

Back

Preview of the front of card 5
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TheRevision2016

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You have miss spelled phagocyte on slide 14

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