Immune System

Question 1

Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable to immune system to identify:

Answer 1

— Pathogens
— Cells from other organisms of the same species
— Abnormal body cells
— Toxins

Question 2

Antigen definition?

Answer 2

Antigens are proteins that are usually part of the cell-surface membranes or cells walls of invading cells, they are recognised as non-self (foreign) by the immune system and stimulates an immune response

Question 3

What are the stages of phagocytosis?

Answer 3

— Phagocyte is attracted to the pathogen by chemoattractants. It moves towards the pathogen through a concentration gradient.
— The phagocyte has several receptors on its cell-surface membrane that attach to chemicals on the surface of the pathogen
— Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium
— The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium
— The hydrolysis products of the bacterium are absorbed by the phagocyte

Question 4

What’s the response of a T lymphocyte to a foreign antigen (cell-mediated response)?

Answer 4

— Helper T cell binds to the complementary antigen presented on the antigen-presenting cell
— Helper T cells are stimulated and divide by mitosis
— Helper T cells also release interleukins, which stimulate B cells to divide to plasma cells to produce antibodies, phagocytosis by phagocytes, and cytotoxic T cells to kill infected cells
— Antigen-presenting cell is performed and presents antigens from the pathogen
— Helper T cells become memory cells

Question 5

Response of B-lymphocytes to a foreign antigen (humoural response)?

Answer 5

— B cells are activated by the binding of the antigen to receptors on its cell membrane
— Helper T cell binds to the antigen on B cells to stimulate it
— B cell divides by mitosis
— This also forms memory cells
— This forms plasma cells that produces antibodies

Question 6

Antibody definition?

Answer 6

Antibodies are proteins with a specific binding site that is synthesised by B cells and bind to foreign antigens.

Question 7

What structures does an antibody have?

Answer 7

— 2 antigen binding sites
— Light chain
— Hevay chain
— receptor binding site
— Variable region
— Constant region

Question 8

How does an antibody lead to the destruction of an antigen?

Answer 8

— They cause agglutination of the bacterial cell. In this way clumps of bacteria cells are formed, making it easier for the phagocyte to locate them as they are less spread-out within the body
— They then become markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 9

The roles of plasma and memory cells in producing the primary and secondary immune response?

Answer 9

B and T cells are made into memory and plasma cells to secrete antibodies because it recognises the foreign antigen. This enables you to fight off the infection very quickly, before the pathogen can divide and start to cause the damage and symptoms of the disease.

Question 10

What’s passive immunity?

Answer 10

Passive immunity is where antibodies are obtained from another organism. They provide short-term immunity. Antibodies are not replaced and no memory cells are formed.

Question 11

What is active immunity?

Answer 11

Active immunity is where antibodies are made by the immune system in response to an infection. Memory cells will remain behind afterwards. Generally long-lasting and is of 2 types: natural active immunity and passive active immunity.

Question 12

What is natural active immunity?

Answer 12

Natural active immunity results from an individual becoming infected with a disease under normal circumstances. The body produces its own antibodies and may continue to do so for many years.

Question 13

What is artificial active immunity?

Answer 13

Forms the basis of vaccination. It involves inducing an immune response in an individual, without them suffering the symptoms of the disease.

Question 14

What is herd immunity?

Answer 14

It’s when a large proportion of the population have been vaccinated to make it difficult the pathogen to spread within the population.

Question 15

What structure does the HIV virus have?

Answer 15

— Attachment protein
— Capsid
— Lipid envelope
— Matrix
— Reverse transcriptase enzyme
— RNA (genetic material)

Question 16

Replication of HIV?

Answer 16

— Following an infection HIV enters the bloodstream and circulates around the body
— A protein on the HIV binds to a protein called CD4
— The protein capsid fuses with the cell-membrane. The RNA and enzymes of HIV enter the helper T cells
— The HIV reverse transcriptase coverts the virus’s RNA into DNA
— The newly made DNA is moved into the T-helper cells nucleus where it’s inserted into the cells DNA
— The HIV DNA in the nucleus creates mRNA using the cells enzymes. This mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV
— The mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles
— The HIV particles break away from the helper T cell with a piece of its cell-surface membrane surrounding them which forms their lipid envelope

Question 17

How does HIV causes symptoms of AIDS?

Answer 17

HIV attacks the T helper cells. AIDS affects the normal functioning of helper T cells. As a results those infected with HIV are unable to respond effectively to other pathogens. It’s the infections, rather than HIV, that ultimately causes ill health and eventually death.

Question 18

What is the procedure of the ELISA test?

Answer 18

— Apply the sample to a surface, for example a slide, to which all the antigens in the sample will attach
— Wash the surface several times to remove any unattached antigens
— Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together
— Wash the surface to remove excess antibody
— Add a second antibody that binds with the first antibody. This second antibody has an enzyme attached to it.
— Add the colourless substrate of the enzyme. The enzyme acts on the substrate to change it into a colourless product
— The amount of the antigen present is relative to the intensity of the colour that develops

Question 19

How are monoclonal antibodies used in targeting medication to specific cells types by attaching a therapeutic drug to an antibody?

Answer 19

— 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 uncontrolled growth

Question 20

What are the ethical issues associated with the use of monoclonal antibodies?

Answer 20

— Involves inducing tumour cells in mice
— There have been deaths and multiple organ failure associated with monoclonal antibodies

Question 21

What are T lymphocytes?

Answer 21

Lymphocytes which migrate to the thymus gland for a period of maturation before migrating to the lymph nodes.

Question 22

What are B lymphocytes?

Answer 22

Lymphocytes which mature in the bone marrow and then migrate to the lymph nodes. B cells produce antibodies.

Question 23

When might a normal cell become an antigen-presenting cell?

Answer 23

— A pathogen such as a virus can gain entry to a normal healthy cell
— As foreign proteins start to be made in the host cell, some of the. Will be presented in the surface membrane

Question 24

What is a cytotoxic T cell?

Answer 24

— Cytotoxic T cells are activated by T helper cells. They divide rapidly.
— Cytotoxic T cells attack and destroy any infected cells. They produce a chemical called performing that makes holes in the cell surface membrane

Question 25

When an antigen binds to a receptor on a T cells, the T cell becomes activated and differentiates into different types of T cells. What are these T cells and what are their functions?

Answer 25

— Cytotoxic T cells kill foreign cells by making holes in their surface membranes
— T helper cells activate B cells and regulates the immune response
— T memory cells remain in the body from previous infections to enable a faster immune response if the body is re-infected

Question 26

What is the action of B lymphocytes?

Answer 26

— One B cells will have an antibody receptor specific to one foreign antigen. These will have a complementary shape.
— The antigen enter the B cell, is processed, and presented on the surface.
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