cell recognition and the immune system- chapter 5

Question 1

what are some more specific longer lasting defense mechanisms and what does it involved

Answer 1

involves a lymphocyte

-cell mediated responses involving T lymphocytes
-Humoral responses involving B-lymphocytes

Question 2

how do lymphocytes recognise your own cells

Answer 2

• Lymphocytes need to be able to distinguish between the body’s own cells and molecules (self) and those that are foreign (non-self)
• Each type of cell has specific molecules on its surface that identify it
• Proteins have a massive variety and a highly specific tertiary structure, it is this variety that distinguishes one cell from another
• These protein molecules which allow the immune system to identify pathogens, non-self material (cells from other organisms of the same species), toxins and abnormal body cells

Question 3

what is the process of phagocytosis

Answer 3

• Chemical products of pathogens or dead, damaged and abnormal cells act as attractants causing phagocytes to move towards the pathogen (e.g. a bacterium)
• Phagocytes have several receptors on their cell-surface membrane that recognise and attach to chemicals on the surface of the pathogen.
• They engulf the pathogen to form a vesicle, known as a phagosome.
• Lysosomes move towards the vesicle and fuse with it.
• Enzyme called lysozymes are present within the lysosome, these destroy ingested bacteria by hydrolysis of their cell walls.
• The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte.

Question 4

what are phagocytes

Answer 4

a type of white blood cells that carry out phagocytosis

Question 5

how do lymphocytes recognise cells belonging to the body

Answer 5

• In the fetus, these lymphocytes are constantly colliding with other cells.
• Lymphocytes will collide almost exclusively with the body’s own material (self)
• Some of the lymphocytes will have receptors that exactly fit those of the bodys own cells.
• Those lymphocytes either die or are suppressed meaning the remaining ones are those that might fit foreign material (non-self).
• In adults, lymphocytes produced in the bone marrow initially only encounter self-antigens and any that show an immune response undergo programmed cell death (apoptosis)

Question 6

what are the two types of lymphocytes and explain them

Answer 6

• B lymphocytes (B cells) mature in the bone marrow. Associated with humoral immunity (immunity involving antibodies that are present in body fluids, or ‘humour’ such as blood plasma’
• T lymphocytes (T cells) mature in the thymus gland. Associated with cell-mediated immunity that is immunity involving body cells

Question 7

what is an antigen

Answer 7

• Any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response

-Usually proteins that are part of the cell-surface membranes or cell walls of invading cells or abnormal body cells.

Question 8

what does the presence of an antigen trigger

Answer 8

the production of an antibody as part of the body’s defence system

Question 9

how do T lymphocytes distinguish invader cells from normal cells

Answer 9

• 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 have different antigens on their cell-surface membrane
• Cancer cells are different from normal body cells and present antigens on their cell-surface membrane.

Question 10

what are cells that display foreign antigens

Answer 10

antigen-presenting cells

Question 11

why is there a vast number of T cells

Answer 11

as the receptors on each T cell respond to a single antigen

Question 12

what are the stages in the response of T lymphocytes to infection by a pathogen (5 steps)

Answer 12

1. Pathogens invade body cells and are taken in by phagocytes.
2. The phagocyte places antigens from the pathogen on its cell-surface membrane
3. Receptors on a specific helper T cell (TH cell) fit exactly onto these antigens.
4. This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells.
5. The cloned T cells:
   a) Develop into memory cells that enable a rapid response to future infections by the same pathogen.
   b) Simulate phagocytes to engulf pathogens by phagocytosis.
   c) Stimulate B cells to divide and secrete their antibody.
   d) Activate cytotoxin T cells (Tc cells)- which produce a protein called perforin that makes holes in the cell-surface membrane.

Question 13

what is the roles of B cells in immunity (7 steps)

Answer 13

1. The surface antigens of an invading pathogen are taken up by a B cell.
2. The 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. The 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 pathogen’s surface.
6. The antibody attaches to antigens on the pathogen and destroys them.
7. Some B cells develop into memory cells. These can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibiotics. This is the secondary immune response

Question 14

what are monoclonal antibodies

in each clone, what do the cells produced develop into

Answer 14

Many different B cells make clones, each of which produces its own type of antibody.
As each clone produce one specific antibody these antibodies are referred to as monoclonal antibodies

plasma cells or memory cells

Question 15

describe plasma cells and their responsibility

Answer 15

secrete antibodies usually into blood plasma.
These cells survive for only a few days, but each can make around 2000 antibodies every seconds.
These antibodies lead to the destruction of the antigen and are responsible for the immediate defence of the body against infection.
The production of antibodies and memory cells is known as primary immune response.

Question 16

describe memory cells and their responsibility

Answer 16

are responsible for the secondary immune response.
They can live up to decades.
When they encounter the same antigen at a later date, they divide rapidly and develop into plasma cells and more memory cells

Question 17

what is the structure of HIV

what group does HIV belong to

Answer 17

• 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 two single strands of RNA and some enzymes.
• One of these enzyme is reverse transcriptase which catalyses the production of DNA from RNA.

retroviruses

Question 18

describe HIV replication

Answer 18

• HIV enters the blood stream and circulates around the body.
• A protein on the HIV readily binds to a protein called CD4, most frequently found on helper T cells.
• The protein capsid fuses with the cell-surface membrane. The RNA and enzymes of HIV enter the helper T cell.
• The HIV reverse transcriptase converts the virus’s RNA into DNA which is then moved into the T cells nucleus where it is inserted into the cell’s DNA.
• The HIV DNA creates messenger RNA using the cell’s enzymes.
• The mRNA passes out of the nucleus through a nuclear pore and uses the cell’s proteins synthesis mechanism to make HIV particles.
• The HIV particles break away from the helper T cell with a piece of the cell-surface membrane surrounding them which forms their lipid envelope

Question 19

how does HIV cause the symptoms of AIDS

Answer 19

• HIV causes aids by killing or interfering with the normal functioning of helper T cells.
• Without a sufficient number of help T cells, 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 become infected and destroyed.

Question 20

what is the ELIZA test

how is the ELIZA test carried out

Answer 20

Uses antibodies to not only detect the presence of a protein in a sample but also the quantity. It is extremely sensitive and so can detect very small amounts.

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 two to bind together.
4. Wash the surface to remove excess antibody
5. Add a second antibody that has an enzyme attached to it that binds with the first antibody.
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 colour that develops

Question 21

why are antibiotics ineffective against viral diseases like AIDS

Answer 21

Antibiotics inhibit certain enzymes required for the synthesis and assembly of the peptide cross-linkages in bacterial cells walls. This weakens the walls, making them unable to withstand pressure. This means water enters naturally by osmosis, the cell bursts and the bacterium dies.

Viruses lack their own metabolic pathogens and cell structures which means antibiotics are ineffective because there is nothing to disrupt. Viruses also have a protein coat rather than murein cell wall and so do not have sites where antibiotics work.

Question 22

what is passive immunity

Answer 22

• Produced by the introduction of antibodies into individuals.
• No direct contact with the pathogen or antigen is necessary.
• Immunity is acquired immediately.
• Antibodies are not being produced by the individuals so they are not replaced when broken down and no memory cells are formed.

Question 23

what is active immunity

what are the 2 types of active immunity and describe them

Answer 23

• Produced by stimulating the production of antibodies by the individuals own immune system.
• Direct contact with the pathogen or its antigen is necessary.
• Immunity takes time to develop but is generally long-lasting

*Natural active immunity- results from an individual becoming infected with a disease under normal circumstances. Body produces its own antibodies.
*Artificial active immunity- forms the basis of vaccination which involves inducing an immune response in an individual without them suffering symptoms of the disease

Question 24

what is a vaccine

Answer 24

• Is the introduction of the appropriate disease antigens into the body via injection or by mouth. Intention is to stimulate an immune response against a particular disease.
• These antigens stimulates an immune response.
• This immune response is small but produces memory cells which remain in the blood allowing a greater and more immediate response to a future infection with the pathogen.

Question 25

what are 5 features of a successful vaccination programme

Answer 25

• must be economically available in sufficient quantities to immunise most of the vulnerable population.
• Few side effects
• Means of producing, storing and transporting the vaccine
• Means of administering the vaccine properly at the appropriate time.
• Must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity

Question 26

why might vaccinations not eliminate a disease (6)

Answer 26

• Vaccination fails to induce immunity in certain individuals.
• May develop the disease immediately after vaccination but before their immunity levels are high enough.
• The pathogen may mutate frequently so its antigens change suddenly. This antigenic variability happens with the influenza virus.
• So many varieties of particular pathogen that it is almost impossible to develop a vaccine that is effective against them all i.e. common cold.
• Certain pathogens ‘hide’ from the body’s immune system i.e. cholera.
• Individuals may have objection to vaccination for religious, ethical or medical reactions.

Question 27

what are the ethics behind using vaccines (6)

Answer 27

• Production of past and future vaccines rely on the use of animals.
• Vaccines have side effects.
• Who should we test the vaccines on?
• Should we trail a new vaccine with unknown health risks only in a country where the targeted disease is common?
• To be fully effective the majority (all) of the population should be vaccinated. Should it be compulsory?
• Should expensive vaccination programmes continue when a disease is almost eradicated?

Question 28

what is the ethical use of monoclonal antibodies (3)

Answer 28

• Production involves the use of mice to produce both antibodies and tumour cells.
• There have been some deaths associated with their use in the treatment of multiple sclerosis.
• Testing for the safety of new drugs presents dangers.

Question 29

how are monoclonal antibodies used in medical diagnosis

Answer 29

• Used in the diagnosis of influenza, hepatitis and chlamydia infection as they produce a much more rapid result.
• Important in diagnosing certain cancers i.e. men with prostate cancer often produce more of a protein (PSA) by using monoclonal antibodies that interact with this antigen it is possible to obtain a measure of the level of PSA in the blood.

Question 30

how are monoclonal antibodies used in pregnancy testing

Answer 30

Monoclonal antibodies present on the test strip of a home pregnancy testing kit are linked to coloured particles. If hCG is present in the urine it binds to 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.

Question 31

how are monoclonal antibodies used in treating cancer

Answer 31

• Monoclonal antibodies can be used to treat cancer in a number of ways but the most successful so far is direct monoclonal antibody therapy
  Monoclonal antibodies are produced that are specific to the 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 cancel cells and block the chemical signals that stimulate uncontrolled cell growth.
• Herceptin- monoclonal antibody used to treat breast cancer, these are highly specific and not toxic leading to a treatment with less side effect.
• Indirect monoclonal antibody therapy which involves attaching a radioactive or cytotoxic drug to the monoclonal antibody.

Question 32

how do antibodies lead to destruction of the antigen (2 ways)

Answer 32

• Cause agglutination of the bacterial cells, this makes it easier for phagocytes to locate them.
• Serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 33

what is an antigen-antibody complex

Answer 33

each antibody has two identical binding sites, which are complementary to a specific antigen to form one

Question 34

what is the antigen made up of

Answer 34

• Made up of four polypeptide chains.
• The chains of one part are long and are called heavy chains, while the chains of the other pair are shorter and are known as light chains.
• The binding site is different on different antibodies and is therefore called the variable region.
• The rest of the antibody is known as the constant region.