Pack 6 - Cell recognition and immune system Part 1

Jacob Shepherd
Mind Map by Jacob Shepherd, updated more than 1 year ago
Jacob Shepherd
Created by Jacob Shepherd about 4 years ago


Information about the immune system

Resource summary

Pack 6 - Cell recognition and immune system Part 1
1 Important definitions:
1.1 A pathogen is an organism that causes a disease
1.2 An antigen is the protein shape on the outside of a cell that stimulates an immune response
1.3 An antibody is a large y-shaped protein molecule that has a specific shape, complimentary to that of one particular antigen
2 Cell identification
2.1 All types of cells have specific molecules on their surface that can be used to identify them
2.1.1 This allows the immune system to identify cells as being self or non-self
3 Defence mechanisms:
3.1 Non-specific mechanisms
3.1.1 Primary defences (barriers to pathogen entry) 1. The skin The cells of the epidermis 2. Mucous membranes Goblet cells produce sticky mucus which traps pathogens 3. HCl in the stomach This denatures proteins/enzymes of pathogens and kills them 4. Tears in the eyes Contains lysozymes this hydrolyses peptidoglycan in bacterial cells 5. Wax in ear canals Traps pathogens
3.1.2 Phagocytosis When physical barriers are breached by pathogens the non-specific immune response takes place Pathogens or infected body cells release a chemical alarm causing the dilation of local blood vessels causing the area to become warm and red The permeability of the capillaries also increases causing swelling This means phagocytic white blood cells move to the area REMEMBER 1. Phagocytes are attracted by chemicals produced by pathogens 2. Phagocyte attaches to pathogen 3. It engulfs the pathogen to form vesicles called phagosomes 4. Lysosomes in phagocytes fuse with phagosomes 5. Hydrolytic enzymes released from lysosomes hydrolyse pathogens 6. Soluble products of digestion are absorbed into the cytoplasm of phagocytes
3.2 Specific Immune Response
3.2.1 This is a response to detection of pathogens or antigens that involves white blood cells called B lymphocytes and T lymphocytes B cells and T cells B lymphocytes originate and mature in the Bone marrow T lymphocytes originate in the bone marrow and mature in the thymus B and T cells have specialised receptor molecules on their cell surface membranes Each cell is capable of recognising one specific shape of antigen Each has different protein receptor molecules on its surface complimentary to the shape of one specific antigen There are not many lymphocytes specific to one antigen Clonal Selection is: The lymphocyte with complimentary protein receptors to those of the pathogen/antigen will be "selected" and stimulated to divide to build up numbers to a level where they can be effective in destroying the pathogen
3.2.2 Cell mediated immunity - T cells T cells respond to an organisms own cells that have been infected by a pathogen 1. Phagocytes and infected body cells place some of the pathogen's antigens on their cell surface - called antigen presentation 2. The helper T cells with the specific receptor for the antigen come into contact with the infected cells and the receptor on the T helper cells binds with the antigen, this is the selection of the correct T lymphocyte 3. This stimulates the selected T cell to divide rapidly by mitosis 4. These cloned T helper cells will: Form T memory cells Stimulate phagocytosis Stimulate B cells to divide and produce antibodies Activate cytotoxic cells 5. Activated cytotoxic T cells kill infected cells by producing a protein called perforin that makes holes in the cell surface membrane This makes the CSM permeable and water and solutes enter/exit freely Ideal for killing virus'
3.2.3 Humoral Immunity - B cells B cells respond to infection by producing antibodies, antibodies are proteins that are soluble in the blood and tissue fluid of the body 1. An antigen enters the blood 2. There will be one B cell that has an antibody on its surface whose shape fits the antigen, the shapes of the antibody and antigen are complementary 3. The specific B cells take in these antigens by endocytosis and present them on the surface of the cell 4. Specific T helper cells attach and stimulate this B cell to divide by mitosis to form a clone of B cells that will produce antibodies to that specific antigen This process is called clonal selection 5. B cells develop into: Plasma cells These cells secrete antibodies into the blood plasma this is the primary response B memory cells These an enable an increased and more rapid response to a second exposure to infection (secondary response)
4 Multiplication of pathogens:
4.1 Bacteria multiply by binary fission
4.2 Virus multiplication:
4.2.1 They enter the host cell and use the host cell's DNA replication and protein production to produce new viral particles
5 Antibody structure
5.1 Made up of:
5.1.1 A constant region
5.1.2 Four polypeptide chains (two light two heavy) held together by disulphide bridges
5.1.3 A variable region, this has a specific shape due to its amino acid sequence. The shape of the variable region and antigen are complementary to each other, this is the antigen binding site
5.1.4 A hinge region that enables antibodies to attach to more than one antigen
5.2 4 polypeptide bonds = quaternary structure
5.2.1 Antigen binding site = tertiary structure Primary structure determines how polypeptide chains fold
6 Agglutination
6.1 Antibodies bind to antigens at the ANTIGEN BINDING SITE at the tip of the variable region
6.1.1 This prepares pathogens for destruction
6.2 Pathogens clump together (loads of antibodies joining to pathogens which join together) and can no longer attack host cells
6.2.1 The clumps are engulfed by phagocytic cells
7 Responses
7.1 Primary Response:
7.1.1 This is the first time the immune system encounters a pathogen, the initial selection of the correct B cell and subsequent cloning take time as there is only one B cell specific to the antigen
7.1.2 Antibodies are secreted into the blood Antibodies attach to and destroy pathogens and any antigens they produce Individual plasma cells only survive for a few days and memory cells survive for a long time
7.2 Secondary response
7.2.1 This is a much greater and quicker response because of the memory cells This is because the memory cells remaining in the cells increase the chance of the B cells of the correct type meeting the pathogen
8 Vaccination
8.1 Vaccination produces immunity to specific diseases by exposing someone to antigenic material that has been rendered harmless
8.2 Active immunity
8.2.1 This is produced by the stimulation of antibodies and memory cells by the body's immune system
8.2.2 Natural active immunity = response by the immune system to infection
8.2.3 Artificial active immunities = response by the immune system to vaccination
8.3 Passive immunity
8.3.1 Produced when antibodies are introduced from an outside source Antibodies are not replaced by the body and no memory cells are produced
8.3.2 Maternal antibodies are passed to foetus from the mother across the placenta Anti-venom given to snake-bite victims
8.4 Herd immunity
8.4.1 When a large proportion of the population is vaccinated it is hard for the pathogen to spread
8.5 Ethics
8.5.1 Development involves animals
8.5.2 Is it fair to make the vaccine compulsory in order to be effective?
8.5.3 Should expensive vaccines continue when a diseases is nearly eradicated
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