2C | Cells and the Immune System Flashcards
What is an antigen?
Antigens are molecules, usually proteins, that can generate an immune response when detected by the body.
What are antigens used to identify?
Pathogens
Abnormal body cells
Toxins
Cells from other individuals of the same species
What is a pathogen?
An organism that can cause disease.
What is an abnormal body cell?
Abnormal body cells are body cells produced by the individual that underwent some sort of mutation to become different, for example cancer cells often have different antigens.
Are toxins antigens?
Yes
Do cells from other individuals of the same species have different antigens to other people?
Yes, though not always
Describe how bacteria are destroyed by phagocytes.
A phagocyte recognizes the foreign antigens on a pathogen.
The cytoplasm of the phagocyte moves around the pathogen, engulfing it.
The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte.
The lysosome (an organelle that contains enzymes known as lysozymes) fuses with the phagocytic vacuole, meaning the enzymes can now interact with the pathogen. The lysozymes hydrolyse the pathogen.
The phagocyte then presents the pathogen’s antigens - it sticks the antigens on its surface to activate other immune system cells.
What is a phagocyte?
A phagocyte (e.g. a macrophage) is a type of white blood cell that carries out phagocytosis, which is the engulfment of pathogens.
They’re found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body.
Give 2 structures that a bacterial cell may have that a white blood cell will not have.
Flagella
Capsule
Plasmid
70S/smaller ribosomes
What is a T-Cell?
A T-cell is another type of white blood cell. It has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes, wherein it is activated.
What is a helper T-cell?
A helper T-cell is a type of white blood cell that releases chemical signals that activate and stimulate phagocytes and cytotoxic T-cells, as well as B-cells.
What are cytotoxic T-cells?
Cytotoxic T-cells are a type of white blood cell that release a chemical called perforin, which form holes in the cell membrane of cells it invades, causing it to leak to death.
What is a B-cell?
B-cells are a type of white blood cell. They’re covered with antibodies - proteins that bind to antigens to form an antigen-antibody complex.
Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens.
Where are B-cells matured?
Bone marrow
Where are T-cells matured?
Thymus gland
Explain the cell-mediated (cellular) immune response.
Firstly, an antigen presenting cell must be found, which can be in the form of a phagocyte, abnormal body cell, body cells from different individuals of the same species or toxins.
Helper T cells have receptors on their surface that fit exactly onto the antigens on antigen-presenting cells (their receptors have a complementary shape to the antigen).
The attachment of antigens to the T-cell receptors causes the T-cell to divide rapidly by mitosis to form many genetically identical (cloned) cells.
The T cells then undergo clonal selection, wherein the new cloned T-cells now either differentiate into Cytotoxic T cells, or stay as Helper T-cells to stimulate B cells for the humoral response or phagocytes for more phagocytosis to take place.
State 2 similarities between B-cells and T-Cells.
Both are a type of white blood cell
Both have a role in immunity and the immune response
State 2 differences between B-cells and T-Cells.
T-Cells are matured in the thymus gland, B-cells are matured in the bone marrow
T-cells are involved in the cellular response
B-cells are involved in the humoral response
Why is the response of T-cells and B-cells specific?
The cells only respond to specific antigens due to the specific shape of their receptors, compared to phagocytes which can respond to any antigen presenting cell.
List and describe the 3 roles played by helper T-cells.
- Are capable of differentiating into Cytotoxic T-cells that produce a chemical called perforin that forms holes into the cell membrane which causes an invading pathogen to leak to death
- Activate other phagocytes to engulf pathogens by phagocytosis
- Stimulate B cells to divide and secrete antibodies
List A to F:
https://media.discordapp.net/attachments/352951793187029005/829447144204140644/unknown.png
B = Light chain C = heavy chain A = antigen binding sites F = variable region E = constant region D = receptor binding site
Describe the structure of an antibody.
Antibodies are proteins synthesized by B-cells.
There is a massive variety of antibodies, with one antibody being complementary to one antigen due to the fact they are made from proteins.
They are made from 4 polypeptide chains, thus they are quaternary.
They have one pair of long chains - these are called ‘heavy’ chains. They are attached by disulfide bridges.
There is also a pair or shorter chains, called ‘light’ chains.
They also have variable regions, which varies between different antibodies.
Outside the variable region where the antigen binding site is, we have the constant region which makes up most of the antibody - this is the area of the antibody that is seen identically between all antibodies.
They also have a receptor binding site where they bind to B cells from.
Antibodies are specific - describe how.
Antibodies are specific, because they have antigen binding sites which are a highly specific shape, meaning they only attach to antigens with a complementary shape to them so they can bind to them by the antigen binding sites, wherein there are 2 of.
Describe why the antigen binding site is known as the variable region.
The reason why the antigen binding site is known as the variable region is because the antigen binding site varies between all antibodies, as each antibody is specific to a different antigen, their antigen binding sites must be a different shape to be complementary to the antigen to successfully bind onto it.
Describe why antibodies made of proteins, rather than carbohydrates or fats, are more likely to be effective against a wide range of diseases.
There must be a massive variety of antibodies as each responds to a different antigen, of which there are millions.
Only proteins have the diversity of molecular structure to produce millions of different types.
Explain how antibodies lead to the destruction of pathogens.
An antibody has two binding sites so can bind to two pathogens at the same time. This means that pathogens become clumped together.
This is called agglutination - this prevents pathogens from binding to the receptor on human cells. It also means that pathogens can recognize the foreign cells and phagocytose many pathogens at one time. This process leads to the destruction of pathogens carrying this antigen in the body at a much faster pace.
What is agglutination?
Agglutination refers to the fact that antibodies have 2 binding sites, and so they are able to bind to 2 pathogens at the same time which allow for pathogens to be clumped together.
Why is agglutination effective at hydrolyzing pathogens at a faster rate?
Agglutination means that many pathogens are clumped up in a small space, meaning that when the phagocyte undergoes phagocytosis, it is able to phagocytose many pathogens at once.
This means that disease is combatted at a much faster rate, as phagocytes would otherwise have to phagocytose one pathogen at a time.
Describe and explain the Humoral response.
Refer to the primary and secondary response in your answer.
When an antigen, for instance, a protein on the surface of a pathogen, foreign cell, damaged or abnormal cell, or a toxin, enters the blood, there will be one B-cell that has one antibody on its surface with a complementary shape to the antigen.
The antibody therefore attaches to this complementary antigen. The antigen enters the cell by a process called endocytosis and gets presented on its surface - it is now known as a processed antigen.
Helper T cells bind to these processed antigens and stimulate the B-cell to divide by mitosis to form a clone of identical B-cells (plasma cells), all of which produce the antibody that is specific to the foreign antigen - these are monoclonal antibodies -many copies of one antibody. This is called clonal selection.
The plasma cells secrete antibodies, usually into the blood plasma. These antibodies lead to the destruction of the pathogen and this is known as the primary immune response.
Memory cells are also produced by B-cells which live longer than plasma cells and do not produce antibodies directly, but if the same antigen is encountered again they divide rapidly into plasma cells and destroy the pathogen very quickly (clonal selection is much quicker). This is the secondary immune response.
List differences between the cellular and humoral response.
Humoral response involves the production of antibodies, cellular response involves no production of antibodies
Cellular response involves no use of B-cells, while humoral response is mostly B-cells
Cellular response is the 1st stage of the immune response, Humoral is 2nd
Cellular response is effective through individual cells, while Humoral response is effective through bodily fluids (usually blood plasma is needed to transport antibodies to desired areas).
Describe how the presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.
The virus antigen must exist in the environment with a B cell that has an antibody attached to it that is complementary to the virus antigen.
The antibody attached to the B cell will attach to the antigen on the virus and makes the antigen enter the cell by endocytosis, making it presented on its surface - this makes it a processed antigen.
A Helper T then cell binds to the antigen presenting cell by their receptor proteins.
This stimulates the B cell with the complementary antibody to divide by mitosis. This produces many clones with the same antibody shape known as plasma cells that release antibodies complementary to the virus antigen.
What are monoclonal antibodies?
Monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells).
This means that they are all identical in structure.
Why are antibodies specific?
They have an unique tertiary structure shown in their variable region where the antigen binding site is present.
Only one particular antigen will be able to fit into the binding sites from having a complementary shape, and so they can only work on an extremely specific range of, if not one, antigen.
Cancer cells are abnormal body cells and thus they have different shapes of antigens.
Drugs have been targeted to a particular cell type. Describe the process.
Cancer cells have antigens called tumour markers - they are not found on normal body cells.
Monoclonal antibodies can be made that will bind to the tumor markers.
You can also attach anti-cancer drugs to the antibodies.
When the antibodies come into contact with the cancer cells they will bind to the tumor markers.
This means the drug will only accumulate in the body where there are cancer cells, so the side effects of an antibody based drug are lower than other drugs because they accumulate near target cells.
Cancer drugs are able to be attached to antibodies which target specific antigens - the drugs then kill the cell the antibody is attached onto.
Describe why cancer drugs that also kill cells but aren’t attached to antibodies are less effective.
Cancer drugs that also kill cells but aren’t attached to antibodies cannot find the difference between a cancer cell, what it’s meant to kill, and a normal cell.
As a result of this, the cancer drug may be wasted and kill cells that are normal and this can cause more side effects.
Since the cancer drug is being used in areas that aren’t cancer cells, due to the fact it isn’t specific, the drug is also less efficient, as it kills less cancer cells.
Targeting a particular substance for medical diagnosis can be seen in pregnancy testing.
Describe the technique used.
Pregnancy tests detect the hormone hCG (Human chorionic gonadotropin). It is found in the urine of pregnant women.
Pregnancy tests take part on a test strip with an application area - the application area contains antibodies for hCG bound to a colored bead (blue).
When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
The urine moves up the stick to the test strip, carrying any beads with it.
The test strip contains antibodies to hCG that are stuck in place (immobili\ed).
If there is hCG present, the test strip turns blue because the immobilized antibody binds to any hCG- concentrating the hCG antibody complex with blue beads attached. If no hCG is present, the beads will pass through the test area without binding to anything, so it won’t go blue.
Describe what the ELISA test attempts to find out.
The ELISA test allows you to see if a patient has any antibodies to a certain antigen, or any antigen to a certain antibody.
It can be used for testing pathogenic infections, for allergies and just about anything you can find an antibody for.
In the ELISA test, an antibody attached to an enzyme is used.
Outline what the function of this is.
An antibody is used in the ELISA test that has an enzyme attached to it.
The antibody is used to carry the enzyme so it can react with a substrate to produce a colored product which would cause the solution in the reaction vessel to change color.
