12.7 Immunology

Question 1

Each type of cell has specific molecules on its plasma cell-surface membrane which help to identify it. These molecules included proteins. What do they enable the immune system to identify?

Answer 1

• Pathogens
• Cells from other organisms of the same species
• Abnormal/cancerous body cells
• Toxins

Question 2

What is an antigen?

Answer 2

A foreign protein that stimulates the generation of antibodies/stimulates an immune response.

Question 3

What is the effect of antigenic variability on disease and disease prevention?

Answer 3

• The secondary immune response is effective as most pathogens have the same antigens on their surface, so they are recognised by memory cells upon reinfection.
• Some antigens mutate/change shape so the pathogen won’t be recognised by memory cells from the previous infection.
• An individual won’t have immune cells with complementary receptors (there will be a different primary and tertiary structure due to mutation).
• An individual’s body will not be able to initiate a secondary response.

Question 4

State two ways that pathogens cause harm/disease.

Answer 4

• Can produce toxins which directly damage tissue.
• Can sometimes replicate inside and destroy host cells.

Question 5

Explain phagocytosis.

Answer 5

• Phagocyte has several receptors complementary to the antigens on the surface of the pathogen, allowing the phagocyte to engulf the pathogen.
• Pathogen is engulfed by phagocyte.
• Lysosomes fuse with the phagosome formed and lysozymes hydrolyse the pathogen into soluble pieces.
• Phagocyte becomes an antigen presenting cell, presents antigens on cell surface membrane.
• Hydrolysis products of bacterium absorbed by phagocyte and released by exocytosis.

Question 6

Explain the cell-mediated response.

Answer 6

• An antigen-presenting cell has antigens on its cell surface membrane. T cells with specifically complementary receptors bind to these antigens
• This stimulates the rapid mitosis of the T helper cells into more T helper cells, cytotoxic killer T cells and memory T cells.
• Memory T cells are part of the secondary response and upon reinfection, these rapidly divide by mitosis to fight off infection.

Question 7

Explain the humoral response.

Answer 7

• T helper cells bind and release cytokines which attract phagocytes and B cells to the area of infection.
• T helper cells bind to specific B cells and stimulate B cells to rapidly divide by mitosis to form clones of plasma B cells (clonal selection).
• Plasma B cells produce antibodies which are a specifically complementary shape to the antigens, so they attach to the antigen and destroy the pathogen.
• Memory B cells are also produced which produce antibodies faster upon reinfection.

Question 8

What is the role of the antigen-presenting cells in the cell-mediated response?

Answer 8

Antigen-presenting cells activate the T helper cells and enable them to rapidly divide by mitosis to produce more T helper cells (cytotoxic killer T cells and memory T cells) which will release cytokines and attract more phagocytes.

Question 9

What is the role of the T helper cells in stimulating cytotoxic killer T cells, B cells and phagocytes?

Answer 9

• Specific T helper cell binds to the antigen-presenting cell, which releases cytokines that attract phagocytes to the area of infection.
• Release cytokines that activate cytotoxic killer T cells.
• Activates specifically complementary B cells.
• Forms memory T cells.

Question 10

What is the role of the cytotoxic killer T cells?

Answer 10

• Locate and destroy infected body cells that present the correct antigen
• Bind to antigen-presenting cells
• Release perforin which creates holes in the cell surface membrane and destroys APC.

Question 11

Define the term antibody.

Answer 11

• An antibody is a specifically complementary protein to an antigen which is produced by plasma B cells. It is made in response to the foreign antigen.

Question 11

Define the term antibody.

Answer 11

• An antibody is a specifically complementary protein to an antigen which is produced by plasma B cells. It is made in response to the foreign antigen.

Question 12

Explain the antibody structure.

Answer 12

• A quaternary structure made of 4 polypeptide chains.
• Y shaped
• Constant region- the main part of the antibody and is the same in all antibodies.
• Variable region- has a different primary structure and therefore different tertiary structure.
• Variable region- have a different primary structure and therefore a different tertiary structure. The binding site is specific and different for each antibody.
• Specific antibodies are only complementary to one antigen and form a permanent antibody-antigen complex.

Question 13

Describe and explain the role of antibodies in stimulating phagocytosis.

Answer 13

• *Agglutination= specific antibodies bind to antigens on pathogens- clump them together. Pathogens attract phagocytes.
• *Opsonisation= binds to antigens and marks pathogens so phagocytes recognise and destroy pathogens efficiently.

Question 14

What is the role of a plasma cell in producing primary immune responses?

Answer 14

Produce and secrete vast quantities of specific antibodies into the blood plasma.

Question 15

What is the role of memory cells in producing secondary immune responses?

Answer 15

• Aren’t involved directly in destroying the invading pathogens.
• Role of the memory cell is to remain in circulation in case of future reinfection by the same pathogen.
• Rapidly activated and rapidly divide by mitosis.
• Differentiate into plasma cells and more memory B cells
• Plasma cells produce lots of specific antibodies for invading pathogens in a short period of time.-

Question 16

What is the role of a vaccine?

Answer 16

• Contains dead, inactive, weakened, or attenuated pathogens.
• Initiates primary response leading to the formation of memory B cells.
• Upon reinfection, the secondary response is stimulated.

Question 17

What is herd immunity?

Answer 17

• If enough individuals in the population are vaccinated there is little chance of disease spreading, therefore even non-vaccinated are protected.
• Immunise the majority of the population.

Question 18

What are vaccination ethics?

Answer 18

• Side effects- usually mild/cause fewer complications than the disease itself- but could be severe/permanent.
• Should vaccinations be compulsory?
• Who should vaccinations be tested on?
• Are they 100% effective long-term?

Question 19

Describe the difference between active and passive immunity.

Answer 19

• Active involves exposure to antigen, passive is no contact with an antigen.
• Active immunity involves memory cells and passive does not.
• Active involves the production of antibodies by plasma/memory cells
• Passive involves antibodies introduced to the body from outside/named source.
• Active is long-term protection because antibodies are produced in response to antigens.
• Passive is short-term because the antibody given is broken down.
• Active can take time to develop/work whereas passive is fast acting/immediate.

Question 20

Explain the structure of HIV.

Answer 20

• Glycoproteins/Attachment proteins specific to receptors on T helper cells on viral lipid envelope.
• Capsid containing the viral RNA and reverse transcriptase.

Question 21

How does HIV replicate in T helper cells?

Answer 21

• Attachment proteins on HIV bind with a receptor protein on T helper cells.
• Capsid fuses with the CSM of the T helper cell.
• Releases genetic info into T helper cells.
• Reverse transcriptase converts viral RNA into cDNA.
• Viral cDNA inserted into human DNA.
• The person is now infected.
• Viral DNA is transcribed into viral RNA and then translated to produce HIV proteins.
• Infected T helper cells manufacture new HIV particles.
• Particles break away from T helper cells with a section of the host cell surface membrane, forming their lipid envelope with specifically complementary T helper receptors embedded.
• Over time this leads to a reduction in the number of T helper cells

Question 22

Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections.

Answer 22

• High viral load leads to increased destruction of helper T/CD4 cells;
• Less activation of B cells/cytotoxic T cells/phagocytes;
• Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
• (Less able to) destroy other microbes/pathogens OR (Less able to) destroy mutated/cancer cells;

Question 23

Why are antibiotics ineffective against viruses?

Answer 23

• Antibiotics prevent bacteria from forming normal cell walls and target 70s ribosomes.
• Viruses use host cell organelles to carry out the metabolic activity.
• Antibiotics kill bacteria.
• Viruses and bacteria replicate in different ways and have different structures

Question 24

What are the uses of monoclonal antibodies?

Answer 24

• Research
• Pregnancy tests/ELISA tests
• Medical diagnosis
• Targeting drugs
• Killing specific cells

Question 25

What are the ethical issues associated with monoclonal antibody usage?

Answer 25

• Mice are used to produce monoclonal antibodies.
• Genetically engineered.

Question 26

Explain the use of antibodies in the ELISA tests.

Answer 26

1. (First) antigen binds/attaches /complementary (in shape) to monoclonal antibody foxed to surface of test well;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen;
4. Washed so any unbound antibodies with enzyme washed away;
5. (Substrate/solution added) and colour changes;

Question 27

State why some antibodies are referred to as monoclonal

Answer 27

(Antibodies) produced from a single clone of B cells / plasma cells;
OR

(Antibodies) produced from the same B cell / plasma cell;

Question 28

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why.

Answer 28

• Specific) primary structure / order of amino acids;
• (Specific) tertiary / 3D structure / shape;
• (So) Only binds to / fits / complementary to one antigen;