3.2.4 Cell Recognition And The Immune System

Question 1

Antigens

Answer 1

Specific molecules in the surface of every cell. These molecules include proteins and enable immune system to identify pathogens, cells from other organisms of the same species, abnormal body cells, toxins

Question 2

Effect of antigen variability on disease and disease prevention

Answer 2

Foreign antigens are detected by the body which generates an immune response

Question 3

Process of phagocytosis

Answer 3

Phagocyte moves towards pathogen via chemotaxis
Phagocyte engulfs pathogen to from phagosome
Phagosome fuses with lysosome to form phagolysosome
Lysozyme digests pathogen
Phagocyte absorbs products from pathogen hydrolysis

Question 4

Cellular response

Answer 4

Phagocyte places antigens from pathogen on cell surface
Receptors on TH cell fit exactly into antigens
Activates T cell + produces cytokines
which simulate T cell to rapidly undergo mitosis
Cloned T cells differentiate into activated T cells
These produce protein called perforin that makes holes in cell membrane so perforated cell becalmed permeable to all substances and the cell dies
Cloned T cells simulate B cells to divide and secrete their antibody
Cloned T cells simulate phagocytes to engulf pathogens by phagocytosis
Develop memory cells that enable a rapid response to future infections

Question 5

T cell

Answer 5

T lymphocyte (white blood cell) 
Has receptor proteins on its surface that bind to complementary antigens presented by phagocytes to activate T cell

Question 6

Helper T cells

Answer 6

TH cells
Release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells
Work with B-cells to produce antibodies

Question 7

Cytotoxic T cells

Answer 7

Tc cells
Kill abnormal and foreign cells
Secrete lymphokines and interferons

Question 8

B cells

Answer 8

B-lymphocytes (type of white blood cell)
Covered in antibodies
Each B cell has different shaped antibody on membrane that bind to specific antigens

Question 9

Antibodies

Answer 9

Proteins that bind to antigens to form antigen-antibody complex

Question 10

Clonal selection

Answer 10

Antibody on B cell surface meets complementary antigen and binds.
With the substances released from helper T cells activated the B cells.
Activated B cell divides into plasma cells

Question 11

Immunity

Answer 11

The ability to be resistant to injury, particularly by poisons, foreign proteins and invading parasites, due to the presence of antibodies

Question 12

Immunoglobulin

Answer 12

An antibody synthesised by plasma cells derived from B-lymphocytes in response to the presence of a specific antigen

Question 13

The immune system

Answer 13

This consists of a number of lymphoid organs linked by lymphatic vessels and capillaries.

The lymphoid organs house billions of lymphocytes which are responsible for identifying and eliminating infectious parasites.

Question 14

Lymphocytes

Answer 14

Large lymphocytes are formed from stem cells in the bone marrow.
The B-lymphocytes make antibodies (humoral response) and are found in the lymphoid organs The T- lymphocytes develop in the thymus, and are concerned not only with cellular immunity but also with the regulation of the humoral response by the B-lymphocytes.

Question 15

Phagocytes

Answer 15

The cells can wander around the body by amoeboid action and will congregate in huge numbers at a site of infection in order to engulf any microbial material. Phagocytes are attracted to sites of infection by chemotaxis.

Question 16

Memory cells

Answer 16

Are programmed to remember the original invading antigen. They remain stored in the lymphoid tissue and if the same antigen is encountered again it is destroyed before disease symptoms occur.

Question 17

Plasma B-cells

Answer 17

Secrete antibodies into the circulation. The antibodies are specific to the pathogenic antigen, which is destroyed

Question 18

Memory B-cells

Answer 18

These are programmed to remember the specific antigen and to respond very rapidly should the body be challenged by that antigen on a subsequent occasion, thus preventing further infection

Question 19

Structure of antibodies

Answer 19

two pairs of polypeptide chains.
2 identical heavy
2 identical light two identical halves held together by disulphide (S-S) bonds. Heavy and light chain also held together by disulfide bridges
Top of chain is variable region

Question 20

Describe how HIV is replicated after entering human cell

Answer 20

Reverse transcriptase 
Enzymes use HIV RNA to make DNA
DNA joined to host cell’s DNA
DNA used to make HIV RNA and capsid at host’s ribosomes 
Assembly of new virus