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Biology Immunity A-level
AQA Biology A-level
Terms in this set (41)
The means by which the body protects itself from infection. It is the main reason why some people are unaffected by certain pathogens.
Who are more vulnerable to infection
The young, elderly and those who are unhealthy
Non specific immunity
Response is immediate and the same for all pathogens e.g. physical barrier (such as skin) or phagocytosis
Response is slower and specific to each pathogen e.g. cell-mediated response (T lymphocytes) and humoral response (B lymphocytes).
Type of white blood cell responsible for the immune response. To defend the body from invasion by foreign material they must be able to distinguish the body's own cells and those that are foreign (non-self). They become activated in the presence of antigens. There are 2 types: T lymphocytes and B lymphocytes.
Cells have specific proteins on their surface that have huge variety and a highly specific tertiary structure- this helps distinguish one cell from another. Also the proteins allow the immune system to identify pathogens, non-specific material, toxins and abnormal body cells.
Mechanism by which cells engulf particles (usually pathogens) to form a vesicle or vacuole.
A type of cell within the body capable of engulfing particles (undergoing phagocytosis). They provide an important defence against the pathogens that manage to enter the body.
A microorganism that causes disease.
Stages of phagocytosis
1- Phagocyte is attracted to pathogen by chemical products of pathogen, it moves along concentration gradient
2- Phagocyte has a lot of receptors on cell-surface membrane that attach to chemicals on surface of pathogen
3- Lysosomes within phagocyte migrate towards phagosome formed by engulfing bacterium
4- Lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium
5- The hydrolysis products of the bacterium are absorbed by the phagocyte
A molecule that triggers an immune response by lymphocytes. It is any part of an organism or substrate that is recognized as non-self (foreign) by the immune system and a immune response is stimulated. They are usually part of the cell-surface membranes or cell walls.
Cells that display foreign antigens on their surface
Type of what blood cell that is produced in the bone marrow but matures in the thymus gland. They coordinate the immune response and kill infected cells. They are associated with cell-mediated immunity which involves body cells. They are also called T cells
Type of white blood cell that is produced and matures within the bone marrow. They produce antibodies as part of their role in immunity. They are involved in humoral immunity which involves antibodies that are present in body fluids. They are also called B cells
Role of T cells in cell-mediated immunity
1- Pathogens invade body cells or taken up by phagocytes
2- Phagocyte places antigens from pathogen on its cell-surface membrane
3- Receptors on a specific helper T cell fit exactly onto these antigens (each T cell responds to a different antigen)
4- This attachment activated T cells to divide rapidly by mitosis and form a clone
5- The cloned T cells either develop into memory cells and enable rapid response in future, stimulate phagocytes to engulf pathogen, stimulate B cells to divide and secrete their antibody or activate cytotoxic T cells
How cytotoxic T cells kill infected cells
They kill abnormal cells and body cells that are infected by pathogens by producing a protein called perforin that makes holes in the cell-surface membrane. The holes means the membrane becomes freely permeable to all substances and as a result the cell dies. It is most effective in viruses as they replicate inside cells and so it stops them from multiplying and infecting more cells
Humoral immunity information
There are many types of B cells and each produces a specific antibody that responds to one specific antigen- they are complementary. This then stimulates division by mitosis and a clone is formed and more specific antibodies are created. Each clone develops into either plasma or memory cells. The antigen enters the B cell by endocytosis and gets presented on the surface.
They secrete antibodies into blood plasma. They only survive for a few days, but each make around 2000 antibodies each second. These antibodies lead to the destruction of the antigen. These cells are responsible for the immediate defence of the body against infection- primary immune response.
They are responsible for the secondary immune response. They live longer than plasma cells. They do not produce antibodies directly, but circulate in the blood and tissue fluid and when they encounter the same antigen later on, they divide rapidly and develop into plasma cells and more memory cells. The new memory cells circulate in readiness for any future infection and so therefore provide long term immunity against the original infection (infection in destroyed before it can cause any harm- we are unaware).
Role of B cells in humoral immunity
1- Surface antigens of an invading cell are taken up by a B cell by endocytosus
2- B cell processes antigens and presents them on its surface
3- Helper T cells attach to processed antigens on B cell
4- B cell is now activated to divide by mitosis to give a clone of plasma cells and memory cells
5- The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogen's surface
6- antibody attached to antigens on pathogen and destroys them
7- Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies.
A protein produced by lymphocytes in response to the presence of the appropriate antigen. They have a specific binding site synthesised by B cells. Each one has 2 specific binding sites which are complementary to a specific antigen. When they combine they form an antigen-antibody complex.
Structure of an antibody
They have 4 polypeptide chains. One pair are long and called heavy chains, the other pair are shorter and called lighter chains. The binding site is different each antibody and is called a variable region. Each binding site has a sequence of amino acids that form a specific 3-D shape that binds directly to a specific antigen. The rest of the antibody is the constant region which binds to receptors on cells.
An antibody produced by a single clone of cells.
They are identical copies of antibodies that have been made in laboratories.
Functions of monoclonal antibodies
- They are very specific so can be used to target specific substances and cells for example cancer cells. The best way to treat cancer is direct monoclonal antibody therapy- monoclonal antibodies are given to a patient and attach themselves to the receptors on their cancer cells and block the chemical signals that stimulate their uncontrolled growth.
- Medical diagnosis- They diagnose infections much quicker than convectional methods of diagnosis. They are important in diagnosing certain cancers. For example with prostate cancer in men they produce more prostate specific antigen so using monoclonal antibodies which interact with the antigen, you can measure the level of PAS in a sample of blood- this gives an early warning.
-Pregnancy testing- Monoclonal antibodies are on the test strip and are linked to coloured particles. If human chorionic gonadatrophin (hCG), which is released by the placenta when a women is pregnant, is present it binds with these antibodies. The hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody creating a coloured line
Ethics of using monoclonal antibodies
- Production of monoclonal antibodies involves the use of mice e.g. production of tumour cells involves inducing cancer in mice.
- Some deaths have been associated with their treatment of multiple sclerosis. Patients should have full knowledge of the risks and benefits of these drugs before giving consent
-Testing for the safety of new drugs presents certain dangers.
It is produced by the introduction of antibodies into individuals from an outside source. No direct contact with the pathogen in needed to induce immunity, it is acquired immediately. As antibodies are not produced by the individual, no memory cells are formed and so there is no lasting immunity. e.g. anti-venom given to victims of snake bites
It is produced by stimulating the production of antibodies by the individual's own immune system. Direct contact with the pathogen or its antigen is necessary and immunity takes time to develop. There are 2 types.
Natural active immunity
It results from individuals becoming infected with a disease under normal circumstances. The body produces its own antibodies and may continue to do so for many years.
Artificial active immunity
It forms the basis of vaccination (immunisation) and involves inducing an immune response in an individual, without them suffering the symptoms of the disease.
The introduction of a vaccine containing appropriate disease antigens into the body, by injection or mouth, in order to induce artificial immunity because memory cells will be produced and will remain n the blood. They are only a precaution and not a treatment.
Features of a successful vaccination programme
- It must be economically available in sufficient quantities to immunise most of the vulnerable population
- Must be no/ few side effects as unpleasant side-effects may discourage individuals in the population from being vaccinated
-Means of producing, storing and transporting the vaccine must be available, it usually includes technologically advanced equipment, hygienic conditions and refrigerated transport.
-Must be a means of administering the vaccine properly at the appropriate time. This means training staff with appropriate skills throughout the population
-It must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity
It arises when a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population
Vaccines do not always work
Even if the criteria for a successful vaccination are met it can still prove extremely difficult to eradicate a disease because:
- vaccinations can fail to induce immunity in certain individuals
- individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent it.
- pathogen may mutate frequently so its antigens change suddenly meaning vaccines suddenly become ineffective as new antigens are no longer recognised by immune system. As a result the immune system doesn't produce antibodies to destroy the pathogen
-may be some varieties of a particular pathogen that is almost impossible to develop a vaccine that is effective against them all.
-some pathogens 'hide' from the body's immune system, either by concealing themselves inside cells, or by living in places out of reach.
some may have objections to vaccination for religious, ethical or medical reasons
Ethics of vaccines
- production of new ones often involves animals
- they have side effects that could cause long term harm
- lots of questions on how they should be carried out, who they should be carried out on
- they are expensive
Structure of the human immunodeficiency virus (HIV)
On the outside is a lipid envelope, embedded in which are peg-like attachment proteins. Inside the envelope is a protein layer called the capsid that encloses 2 single strands of RNA and enzymes. One of these enzymes is reverse transcriptase which catalyses the production of DNA from RNA- the reverse is carried out by transcriptase. HIV belongs to a group of retroviruses because of it.
Replication of HIV
Since HIV is a virus it cannot replicate itself, instead it uses genetic material to instruct the hosts cell's biochemical mechanisms to produce the components required to make new HIV. How it does this: - A protein on the HIV readily binds to a protein called CD4 which is most likely a T cell
- the protein capsid fuses with the cell-surface membrane and the RNA and enzymes of HIV enter the helper T cell
- HIV reverse transcriptase converts HIV's RNA into DNA which is then moved into the helper T cell's nucleus where it's inserted into the cell's DNA
- HIV DNA nucleus creates messenger RNA using cell's enzymes. This mRNA contains instructions for making new viral proteins and the RNA to go into the new HIV
- mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles
- HIV particles break away from the helper T cell with a piece of its cell-surface membrane surrounding them which forms their lipid envelope
How HIV causes symptoms of AIDS
HIV causes AIDS by killing or interfering with the normal functioning of helper T cells. T cells are important in cell- mediated immunity so without a sufficient number of them the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill cells infected by pathogens. Memory cells may also be infected or destroyed. Therefore the body is unable to produce an adequate immune response and becomes susceptible to other infections.
ELISA (enzyme linked immunosorbant assay) test
Uses antibodies to detect presence of a protein in a sample and the quantity. It is sensitive so can detect very small amounts of a molecule.
how do cytotoxic t cells kill infected cells
produce a protein called perforin
makes holes in the cell surface membrane
so it becomes permeable to all substances, and bursts
prevents replication inside cells ie viruses
process by which a cell takes material into the cell by infolding of the cell membrane
action of memory cells
secondary immune response
circulate the blood
when they encounter the same antigen they divide to produce plasma and memory cells
memory circulate again while plasma produce antibodies to destroy the pathogen
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