Cell recognition and the immune system

Question 1

Describe how the immune system identifies its own cells

Answer 1

Each type of cell has specific molecules (proteins) on it cell surface. On its own cells these are self antigens which the immune system doesn’t make antibodies.

Question 2

How do pathogens trigger the immune system?

Answer 2

The non-self antigens on its cell surface membrane will trigger the productions of antibodies

Question 3

What type of cells does the immune system identify?

Answer 3

-Pathogens
-cells from other organisms of the same species
-abnormal body cells
-cancer cells

Question 4

Define antigen

Answer 4

A protein molecule found on the cell surface membrane of cells that stimulates an immune response.

Question 5

What is antigen variability

Answer 5

the ability of pathogens to change their surface antigens ( normally through a mutation in their genetic material)

Question 6

What is the effect of antigen variability on disease prevention (vaccines)

Answer 6

Vaccine becomes ineffective as the new antigens are no longer recognised by the immune system which means it doesn’t produce the antigens to destroy the pathogen.

Question 7

Explain phagocytosis (steps)

Answer 7

-Pathogen with antigens on its surface
-Phagocyte is attracted to pathogen through its receptors on its surface and attaches to the antigens
-Phagocyte engulfs the pathogen forming a phagosome
-Lysosome fuses with the phagosome and releases a lysozome enzyme which hydrolyses the pathogen
-The product of the hydrolysis are absorbed by the pathogen.

Question 8

Describe T lymphocytes response to a foreign antigen (steps)

Answer 8

-phagocytosis
-Phagocyte presents the antigens onto its cell surface membrane (APC)
-Specific receptors on the helper T cells attach to the antigen
-This activates the helper T cell to divide by mitosis to form clones.
-Some of these clones differentiate into memory cells which stay in the blood and allow a quicker response if re-infected with the same pathogen.
-Some remain as helper T cells and activate phagocytosis, activate cytotoxic T cells and stimulate B cells to divide.

Question 9

Describe the response of B lymphocytes to a foreign antigen (steps)

Answer 9

-Antigen of pathogen are taken up by the B cell and presented onto its cell surface membrane
-Helper T cell is binds to the antigens and activates the B cell (clonal selection)
-The activated B cell then divides by mitosis to form clones (clonal expansion)
-Some differentiate into memory B cells which remain in the blood and can differentiate into plasma cells if re-infected with the same pathogen.
-Some differentiate into plasma cells which produce the specific antibodies for (/complementary to) the antigen.

Question 10

What defence mechanism is slower

Answer 10

specific

Question 11

what defence mechanism is immediate

Answer 11

non-specific

Question 12

Give examples of non-specific defence mechanisms

Answer 12

-physical barrier (skin)
-Phagocytosis

Question 13

Give examples of specific defence mechanisms

Answer 13

-Cell mediated immunity
-Humoral immunity

Question 14

T lymphocytes

Answer 14

-Type of white blood cell
made in bone marrow
-mature in thymus gland
-involved in cell mediated immunity

Question 15

B lymphocyte

Answer 15

-type of white blood cell
-made and matures in bone marrow
-involved in humoral immunity

Question 16

What are the differences between humoral response and cell mediated immunity

Answer 16

-cell mediated immunity involved T cells, whereas humoral response mainly involves B cells
-Cell mediated immunity doesn’t produce antibodies but humoral response does
-Cell mediated immunity is the first stage of the immune response whereas humoral response is the second stage.
-Cell mediated immunity is effective through cells, whereas humoral response is effective through body fluids

Question 17

Define antibody

Answer 17

-A protein with receptors that have a complementary shape to bind to a specific antigen

Question 18

Describe the structure of an antibody

Answer 18

-quaternary structure
-has disulphide bridges, variable region, antigen binding sites and short and long chains

Question 19

What is the role of the disulphide bridges in an antibody

Answer 19

To hold/join together the 4 polypeptide chains

Question 20

Why is the primary immune response slower

Answer 20

time taken for antigen presentation, clonal selection, clonal expansion and differentiation of B cells into plasma cells and then the production of antibodies is slower as there are no memory cells

Question 21

Why is the secondary immune response faster

Answer 21

The memory cells allow clonal expansion of the correct B cell to happen quickly which allows faster differentiation into plasma cells which secrete more antibodies faster.

Question 22

How do antibodies destroy pathogens?

Answer 22

-An antigen-antibody complex is formed
-Antigen binding site on the antibody is specific and will only bind to the antigen with the complementary shape
-Agglutination (clumps of bacterial cells form)
-Acts as markers for phagocytes to engulf them

Question 23

Define a vaccine

Answer 23

Contains antigens from the pathogen and stimulates the production of antibodies and memory cells against the target pathogen without causing the disease

Question 24

How do vaccines prevent a person from developing a certain disease

Answer 24

-produces a primary immune response
-memory B cells are made
-Exposure to the pathogen means memory cells differentiate into plasma cells faster so the antigens are made more quickly and in large numbers before symptoms can occur

Question 25

Define herd immunity

Answer 25

A form of immunity that occurs when the vaccination of a significant portion of the population provides a measure of protection for individuals who have not developed immunity
makes it less likely to spread

Question 26

What is active immunity

Answer 26

The individual produces their own antibodies as they have had direct contact with the pathogen

Question 27

What is passive immunity

Answer 27

The individual receives antibodies

Question 28

What is the difference between natural and artificial active immunity

Answer 28

natural active immunity is when a person has become infected by the disease, artificial is through the basis of immunization/ vaccines

Question 29

What is the difference between natural and active passive immunity

Answer 29

Natural is where the antibodies pass across placenta for fetus or breast milk for babies, artificial is where ready made antibodies are given to a person

Question 30

What are the differences between active immunity and passive immunity
-Memory B cells
-Antibodies outside source
-Long term/short term
-takes time/fast acting

Answer 30

-Active immunity involves memory B cells, passive immunity doesn’t
-Active immunity is where the antibodies are not introduced by outside source, passive immunity they are
-Active immunity is long term, passive immunity is not
Active immunity takes time to develop, passive immunity is fast acting

Question 31

What does HIV stand for

Answer 31

Human immunodeficiency virus

Question 32

What is the structure of HIV

Answer 32

-Genetic material (RNA)
-attachment protein (allows attachment to the receptor of the host cell/ helper T cell
-Lipid envelope (phospholipid bilayer)
-Capsid (encloses the enzyme and the 2 strands of RNA)
- reverse transcriptase enzyme

Question 33

What cells does HIV infect and destroy

Answer 33

Helper T cells

Question 34

Describe how HIV is replicated

Answer 34

-Attachment proteins attach to receptor molecules on the cell membrane of the helper T cell
-The capsid is released into the cell, where it un-coats and releases the genetic material (RNA) into the cell cytoplasm
-Inside the cell, reverse transcriptase enzyme is used to make complementary strand of DNA from the viral RNA template
-Double strand DNA is made and inserted into the human DNA
-Host cell enzyme are used to make viral proteins from the viral DNA ( found within the human DNA)
-The viral proteins are assumed into new viruses bud from the cell