3.2 cells- immunity

Question 1

what is the process of phagocytosis

Answer 1

1. During phagocytosis, the phagocyte first recognises a foreign marker on the pathogen’s outer membrane, called the antigen
2. Small non-specific protein molecules called opsonin’s then attach to the antigen
3. The phagocyte can then bind to the opsonin attached to the pathogen antigen- allowing the phagocyte to get closer to the pathogen
4. The pathogen is then engulfed and enclosed in a large vacuole called a phagosome
5. The phagosome then fuses with lysosomes which are vesicles containing digestive enzymes called lysozyme. This causes the lysozymes to be released and they break down the pathogen
6. There are a few special cells like macrophages that do not completely destroy the pathogen and instead save the pathogen antigen. They put the pathogen antigen on a special protein complex.
7. This then moved to the cell surface membrane so other immune cells can recognise the pathogen antigen. The cells that do this are called antigen presenting cells

Question 2

what is an antigen

Answer 2

Any part of an organism or substrate that is recognised as non-self by the immune system and stimulates an immune response.
Are usually proteins that are part of the cell-surface membranes or cell walls of invading cells

Question 3

what is an antigen

Answer 3

Any part of an organism or substrate that is recognised as non-self by the immune system and stimulates an immune response.
Are usually proteins that are part of the cell-surface membranes or cell walls of invading cells

Question 4

cell mediated immunity

Answer 4

Lymphocytes respond to an organisms own cells that have been infected by non-self material from different species. Respond to cells from other individuals of the same species because they are genetically different. These therefore have a different antigen of the cell-surface membrane from the antigen on the organisms own cells.

Question 5

why can T lymphocytes tell if a cell is an invader cell

Answer 5

• Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogens antigens on their own cell-surface membrane.
• Body cells invaded by a virus present some of the viral antigens on their own cell surface membrane.
• Transplanted cells from individuals of the same species have different antigens on their cell-surface membrane
• Cancer cells are different from normal body cells and present antigens on the cell-surface membranes

Question 6

what is the cell mediated immunity response

Answer 6

• Pathogens invade the body cells or are taken in by phagocytes
• Phagocytes place antigens from the pathogen on its cell-surface membrane
• Receptors on a specific helper T cell, fit exactly onto these antigens
• This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells

Question 7

in the process of cell mediated immunity, what do the cloned T cells do

Answer 7

1. Develop into memory cells that enable a rapid response to future infections by the same pathogen
2. Stimulate phagocytes to engulf pathogens by phagocytosis
3. Stimulate B cells to divide and secrete their antibody
4. Activate cytotoxic T cells

Question 8

in the process of cell mediated immunity, what do the cloned T cells do

Answer 8

1. Develop into memory cells that enable a rapid response to future infections by the same pathogen
2. Stimulate phagocytes to engulf pathogens by phagocytosis
3. Stimulate B cells to divide and secrete their antibody
4. Activate cytotoxic T cells

Question 9

how do cytotoxic T cells kill infected cells

Answer 9

Kill abnormal cells and body cells that are infected by pathogens, by producing a protein called perforin that makes hole in the cell-surface membrane.
The holes means that the cell surface membrane becomes permeable to all substances and the cell dies as a result.

Question 10

what are lymphocytes

Answer 10

The body has specific responses that react to certain antigens, they are slower in action at first but can provide long-term immunity.
This depends on a type of white blood cell called a lymphocyte that are produced by stem cells in the bone marrow.

Question 11

why are B cells called B cells

Answer 11

B lymphocytes ( B cells) are called so because they mature in the bone marrow. Are associated with humoral immunity.

Question 12

why are T cells called T cells

Answer 12

T lymphocytes ( T cells) are so called because they mature in the thymus gland. Are associated with cell-mediated immunity.

Question 13

what is humoral immunity

Answer 13

Is so called because it involves antibodies and antibodies are soluble in the blood and tissue fluid of the body.
Each B cell starts to produce a specific antibody that responds to a antigen. When an antigen enters the blood or tissue fluid, there will be a B cell who has an antibody on its surface whose shape is complementary to that of the antigen and so attaches to the antigen.

Question 14

what is clonal selection part of humoral immunity

Answer 14

The antigen enters the B cell by endocytosis and gets presented on its surface. Helper T cells bind to these processed antigens and stimulates the B cell to divide by mitosis to form a clone of identical B cell that produce the correct antibody that is specific to the antigen.
Is called clonal selection.

Question 15

what do humoral immunity clones make

Answer 15

Toxins act as an antigen and so many different B cells makes clones, each of which produces its own antibodies. These antibodies are referred to as monoclonal antibodies.
In each clone, the cells produced develop into one of 2 types of cell:
Plasma cells
Memory cells

Question 16

what is plasma cells

Answer 16

the primary immune response
secrete antibodies usually into blood plasma.
Survives for a few days but each can make around 2,000 antibodies each second during its brief lifetime. These antibodies lead to the destruction of the antigen. Are responsible for the immediate defence of the body against infection

Question 17

what is memory cells

Answer 17

the secondary immune response.
Live considerably longer than plasma cells.
Don’t produce antibodies directly but circulate in the blood and tissue fluid. When they encounter the antigen, they divide rapidly and develop into plasma cells and more memory cells. The plasma cells produce the antibody needed to destroy the pathogen and the new memory cells circulate the blood.

Question 18

what is the process of humoral immunity

Answer 18

1. Surface antigens of an invading pathogen are taken up by a B cell
2. B cell processes the antigens and presents them on its surface
3. Helper T cells attach to the processed antigens on the B cell thereby activating the B cell
4. B cell is now activated to divide by mitosis to give a clone of plasma cells
5. The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
6. The antibody attaches to antigens and destroys them
7. Some B cells develop into memory cells that can respond to further infections by the same pathogen

Question 19

what are antibodies

Answer 19

Are proteins with specific binding sites synthesised by B cells. When the body is infected by non-self material, a B cell produces a specific antibody. This specific antibody reacts with an antigen on the surface of non-self material by binding to it.
Each antibody has 2 identical binding sites. The antibody binding sides are complementary to a specific antigen. The specific binding sites are called the antigen-antibody complex.

Question 20

what is the structure of antibodies

Answer 20

Made up of 4 polypeptide chains. A pair of chains are long and are called heavy chains and the other pair are shorter and are known to be light chains
[see physical flashcard for diagram

Question 21

what is the variable region

Answer 21

antibody-antigen complex is different on different antibodies

Question 22

how do antibodies ‘destroy’ antigens

Answer 22

Don’t destroy antigens directly but prepare them for destruction. Different antibodies lead to the destruction of antigens in a number of ways.

Question 23

how do antibodies break down bacterial cells

Answer 23

Cause agglutination of bacterial cells. In this way, clumps of bacterial cells are formed, making it easier for the phagocytes to locate them as they are less spread out
Then serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 24

what are monoclonal antibodies

Answer 24

Each antigen will induce a different B cell to multiply and form a clone of itself. Each of these clones will produce a different antibody. It is even better if a single type of antibody can be isolated and cloned. Such antibodies are known as monoclonal antibodies

Question 25

how are monoclonal antibodies used in medical diagnosis

Answer 25

Are an invaluable tool in diagnosing disease with over a hundred different diagnostic products based on them. Used for the diagnosis of influenza, hepatitis and chlamydia infections where they produce a more rapid result than conventional methods. Important in diagnosing certain cancers E.g. men with prostate cancer often produce more of a protein called prostate specific antigen (PSA), leading to unusually high levels of it in the blood. By using monoclonal antibodies that interacts with the antigen, it is possible to obtain a measure of the levels of PSA in the blood. While a higher level than normal of PSA isn’t a diagnosis in itself, it gives an early warning of its possibility and the need for further tests

Question 26

how can monoclonal antibodies be used for treatment

Answer 26

As an antibody is very specific to a particular antigen, monoclonal antibodies can be used to target specific substances and specific cells. 1 type of cell they can target is cancer cells. Can be used to treat cancer in a number of ways. The most successful is direct monoclonal antibody therapy, the other method is indirect monoclonal antibody therapy.

Question 27

what is direct monoclonal antibody therapy

Answer 27

Monoclonal antibodies are produced that are specific to antigens on cancer cells. These antibodies are given to a patient and attach themselves to the receptors on their cancer cells They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrollable growth

Question 28

what is indirect monoclonal antibody therapy

Answer 28

which involves attaching a radioactive or cytotoxic drug to the monoclonal antibody. When the antibody attaches to the cancer cells, they kill them.

Question 29

what are ethical issues with monoclonal antibodies

Answer 29

Production involves the use of mice, which are used to make both antibodies and tumour cells. Involves deliberately inducing cancer Has been used to successful treat a number of diseases including cancer and diabetes. Has also been deaths associated with use in the treatment of multiple sclerosis. Testing for the safety of new drugs presents certain dangers,

Question 30

what is active immunity

Answer 30

Produced by stimulating the production of antibodies by the individuals own immune system. Direct contact with the pathogen or antigen is necessary. Immunity takes time to develop and is generally long-lasting and is of 2 types: natural active immunity artificial active immunity

Question 31

what is natural active immunity

Answer 31

Natural active immunity- results form an individual becoming infected with a disease under normal circumstances

Question 32

what is artificial active immunity

Answer 32

Artificial active immunity- forms the basis of vaccination. Involves inducing an immune response in an individual, without them suffering the symptoms

Question 33

what is passive immunity

Answer 33

Produced by the introduction of antibodies into individuals from an outside source, no direct contact with pathogen or antibody is necessary to induce immunity. Immunity is acquired immediately. As the antibodies aren’t being produced by the individual, the antibodies aren’t replaced when they are broken down and no memory cells are produced, so there is no lasting immunity.

Question 34

what is herd immunity

Answer 34

Arises when a sufficiently large population has been vaccinated to make it difficult for a pathogen to spread within that population.

Question 35

what is vaccinations

Answer 35

The introduction of the appropriate disease antigens into the body either by injection or by mouth. The intention is to stimulate an immune response against a disease. It contains 1 or more types of antigen from the pathogen. Produces a slight response. Memory cells are produced.

Question 36

what are the ethical issues with vaccinations

Answer 36

The production of existing and new vaccines often involve animals Vaccines have side-effects that may sometimes cause long-term harm To what extent should individuals be asked to accept risk in the interest of public health?

Question 37

what is the structure of HIV

Answer 37

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 strands of RNA and some enzymes One of the enzymes is reverse transcriptase ( catalyses the production of DNA from RNA- reverse reaction to transcriptase) [See physical flashcard for diagram]

Question 38

what is the process of HIV replication

Answer 38

1. HIV enters bloodstream and circulates around the body 2. A protein on the HIV readily binds to a protein called CD4. while this protein occurs on a number of cells, HIV most frequently attaches to T helper cells 4. The protein capsid fuses with the cell-surface membrane. The RNA and enzymes of HIV enter the helper T cell 5. HIV reverse transcriptase converts the viruses RNA into DNA 6. Newly made DNA is moved into T helper cell’s nucleus where it is inserted into the cell’s DNA. HIV DNA in the nucleus makes mRNA using the cell’s enzymes. 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 cell’s protein synthesis mechanism to make new HIV particles, 7. HIV particles break away from helper T cell with a piece of its cell-surface membrane surrounding them which makes the lipid envelope

Question 39

why must HIV replicate in the way it does

Answer 39

Cannot replicate itself and so uses genetic material to instruct the host cell’s biochemical mechanisms to produce the components required to make a new HIV

Question 40

how does HIV cause AIDS

Answer 40

Cannot replicate itself and so uses genetic material to instruct the host cell’s biochemical mechanisms to produce the components required to make a new HIV

Question 41

what is the ELISA test

Answer 41

Enzyme linked immunosorbent assay. Uses antibodies to detect the presence of a protein in a sample and the quantity. Extremely sensitive and so can detect very small amounts of a molecule.

Question 42

how does the ELISA test work

Answer 42

1. Apply the sample to a surface to which all the antigens in the sample will attach 2. Wash the surface several times to remove any unattached antigens 3. Add the antibody that is specific to the antigen we are trying to detect and leave the 2 to bind together. 4. Wash the surface to remove excess antibody 5. Add a 2nd antibody that binds with the 1st antibody. The 2nd has an enzyme attached it. 6. Add the colourless substrate of the enzyme. The enzyme acts on the substrate to change it into a coloured product. 7. The amount of the antigen present is relative to the intensity of the colour that develops.