Cell Recognition & the Immune System (AQA A Level Biology): Flashcards
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Define antigen.
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Define antigen.
An antigen is a surface molecule present on cells, viral particles, or toxins that enables the body to identify self and non-self.
True or False?
Only proteins on the cell surface can act as markers for cell recognition.
False.
While surface proteins such as glycoproteins are common markers, glycolipids can also act as markers for cell recognition.
The body distinguishes between its own cells (‘self’) and foreign cells (‘non-self’) using on the surface of cells.
The body distinguishes between its own cells (‘self’) and foreign cells (‘non-self’) using specific molecules on the surface of cells.
What are three examples of foreign entities that the immune system can recognise using cell surface markers?
The immune system can recognise pathogenic cells, abnormal body cells (such as cancerous or pathogen-infected cells), toxins, and cells from other individuals of the same species.
For a successful organ transplant, the body must not the cells and tissues of the donated organ as foreign to prevent an immune .
For a successful organ transplant, the body must not recognise the cells and tissues of the donated organ as foreign to prevent an immune response.
Cell surface markers are usually , such as glycoproteins, present on the bilayer.
Cell surface markers are usually proteins, such as glycoproteins, present on the phospholipid bilayer.
What do the terms ‘self’ and ‘non-self’ mean in cell recognition?
Self refers to the body’s own cells, while non-self refers to foreign cells and particles.
True or False?
Viral particles also have surface molecules that the body can use to identify them.
True.
Specific molecules on the surface of cells and viral particles enable the body to identify them.
Which two types of surface molecule commonly act as markers for cell recognition?
Glycoproteins and glycolipids commonly act as markers for cell recognition.
The body uses surface molecules called , present on cells, viral particles and toxins, to identify self and non-self.
The body uses surface molecules called antigens, present on cells, viral particles and toxins, to identify self and non-self.
Why must a transplant recipient’s body not recognise the donor organ’s cells as foreign?
So that no immune response occurs against the donated organ, allowing the transplant to be successful.
Define antigen.
An antigen is a unique macromolecule found on the surface of cells or pathogens that enables cell-to-cell recognition and helps the immune system distinguish between self and non-self.
What is the difference between self antigens and non-self antigens?
Self antigens are produced by the body’s own cells and do not trigger an immune response, while non-self antigens are found on foreign cells and stimulate an immune response.
Glycolipids and glycoproteins on membranes often act as .
Glycolipids and glycoproteins on membranes often act as antigens.
How does antigenic variability in pathogens like the flu virus affect immunity?
Antigenic variability causes the pathogen's surface antigens to change, so existing lymphocytes and memory cells can no longer bind, preventing a secondary immune response. As a result, the host can be infected again.
Vaccines for the virus must be updated regularly due to .
Vaccines for the flu virus must be updated regularly due to antigenic variability.
Antigens are macromolecules found on cell membranes, walls, or surfaces.
Antigens are macromolecules found on cell membranes, bacterial walls, or viral surfaces.
What is the main function of antigens?
Antigens enable cell-to-cell recognition and help the body distinguish between self and non-self cells.
Why do some pathogens show antigen variability?
They undergo frequent genetic mutations, which change their surface antigens.
Name two types of pathogen that commonly show antigen variability.
Cold and flu viruses commonly show antigen variability.
Define non-self antigen.
A non-self antigen is a large molecule found on foreign cells (such as pathogens or incompatible blood cells) that stimulates an immune response.
True or False?
Non-self antigens do not trigger an immune response.
False.
Non-self antigens stimulate an immune response; it is self antigens that do not trigger one.
Define phagocytosis.
Phagocytosis is the process by which phagocytes recognise and engulf pathogens, forming a phagocytic vacuole for their digestion.
What are the two main types of phagocyte in humans?
The two main types of phagocyte in humans are neutrophils and macrophages.
True or False?
Phagocytosis is a specific immune response.
False.
Phagocytosis is a non-specific immune response.
During phagocytosis, phagocytes are attracted to sites of infection by released from pathogens or damaged cells.
During phagocytosis, phagocytes are attracted to sites of infection by chemicals released from pathogens or damaged cells.
The vacuole containing the engulfed pathogen is called a .
The vacuole containing the engulfed pathogen is called a phagosome.
Define phagolysosome.
A phagolysosome is a structure formed when a phagosome fuses with a lysosome, allowing enzymes to digest the pathogen.
What is the role of antigen presentation in macrophages?
In macrophages, antigen presentation involves displaying pathogen fragments on the cell surface to activate the specific immune response.
Where are phagocytes produced?
Phagocytes are white blood cells produced continuously in the bone marrow.
How do phagocytes recognise pathogens during phagocytosis?
Phagocytes use receptor proteins on their membrane to detect and bind to non-self antigens on the pathogen’s surface.
A phagocyte engulfs a pathogen by extending its membrane around it, forming a phagocytic vacuole; this is an example of .
A phagocyte engulfs a pathogen by extending its membrane around it, forming a phagocytic vacuole; this is an example of endocytosis.
During digestion, are released to hydrolyse the pathogen, for example by breaking down bacterial cell walls.
During digestion, lysozymes are released to hydrolyse the pathogen, for example by breaking down bacterial cell walls.
Define lymphocyte.
A lymphocyte is a type of white blood cell involved in the specific immune response.
What are the two main types of lymphocytes and their roles?
The two main types of lymphocytes are T-lymphocytes (which destroy infected body cells in the cellular response) and B-lymphocytes (which produce antibodies in the humoral response).
Lymphocytes are produced in the before birth and have a that fills most of the cell.
Lymphocytes are produced in the bone marrow before birth and have a large nucleus that fills most of the cell.
What is an antigen-presenting cell?
An antigen-presenting cell is a host cell that has been invaded by a pathogen and displays the pathogen's antigen on its cell surface membrane.
Define T helper cell.
A T helper cell is a type of T-lymphocyte that is activated by binding to its specific antigen on an antigen-presenting cell and then stimulates other immune cells by releasing cytokines.
Activated T helper cells release , which stimulate the maturation of B-lymphocytes into .
Activated T helper cells release cytokines, which stimulate the maturation of B-lymphocytes into antibody-secreting plasma cells.
What is the role of cytotoxic T cells (T killer cells)?
Cytotoxic T cells patrol the body for infected cells displaying foreign antigens, bind to them, and release perforins and other toxic substances to destroy the infected cells and pathogens.
Antigens are displayed on on the cell surface membrane to activate specific T cells.
Antigens are displayed on major histocompatibility complexes (MHCs) on the cell surface membrane to activate specific T cells.
True or False?
T helper cells stimulate the production of memory B and T cells by releasing cytokines.
True.
T helper cells release cytokines which stimulate the production of memory B and T cells.
Define B lymphocyte.
A B lymphocyte is a type of white blood cell that has a specific antibody on its surface, allowing it to bind to complementary antigens as part of the humoral immune response.
What is the role of the antibody receptor on a B lymphocyte?
The antibody receptor on a B lymphocyte allows it to bind to a complementary antigen, triggering activation of the B cell as part of the immune response.
Each mature B lymphocyte has a on its surface, which acts as a receptor.
Each mature B lymphocyte has a specific antibody on its surface, which acts as a receptor.
Define humoral response.
The humoral response is the branch of the immune system in which B lymphocytes produce antibodies to target pathogens in body fluids.
What is the difference between clonal selection and clonal expansion in B lymphocytes?
Clonal selection is when a B lymphocyte binds to its complementary antigen and becomes activated, while clonal expansion is the subsequent process where the activated B lymphocyte divides by mitosis to produce many identical cells.
After clonal selection, B lymphocytes undergo , producing many identical cells.
After clonal selection, B lymphocytes undergo clonal expansion, producing many identical cells.
What are the two main types of cells produced when activated B lymphocytes divide?
Activated B lymphocytes divide to produce plasma cells that secrete antibodies, and memory cells that provide long-term immunity.
The immune response is slow because it takes time to make enough antibodies.
The primary immune response is slow because it takes time to make enough antibodies.
Define antigen-antibody complex.
An antigen-antibody complex forms when an antibody binds to its complementary antigen, fitting together due to their complementary shapes.
What happens when an antibody binds to a non-self antigen with a complementary shape?
When an antibody binds to a non-self antigen with a complementary shape, they form an antigen-antibody complex.
When antibodies bind to antigens on pathogens, this can cause of the pathogens, making them easier targets for phagocytes.
When antibodies bind to antigens on pathogens, this can cause agglutination of the pathogens, making them easier targets for phagocytes.
Define agglutination.
Agglutination is the process where antibodies bind to multiple antigens on pathogens, causing them to clump together.
True or False?
Agglutination helps phagocytes engulf many pathogens at once.
True.
Agglutination clumps pathogens together, making it easier for phagocytes to engulf and destroy them all at once.
Define antibody.
An antibody is a globular glycoprotein with a quaternary structure, shaped like a Y, made of two heavy and two light polypeptide chains joined by disulfide bonds.
Each antibody has a region, which is the same within one class, and a region, which is different for each antibody.
Each antibody has a constant region, which is the same within one class, and a variable region, which is different for each antibody.
What determines the specificity of an antibody for its antigen?
The amino acid sequence in the variable region determines the shape of the antigen-binding site, giving the antibody its specificity for a particular antigen.
The antigen-binding site of an antibody is specific to the on the antigen, known as the .
The antigen-binding site of an antibody is specific to the region on the antigen, known as the epitope.
True or False?
The hinge region in an antibody gives it flexibility to bind antigens at different angles.
True.
The hinge region in the heavy chain of some antibodies allows flexibility for the antigen-binding sites to bind antigens at various angles.
How many antigen-binding sites does a typical Y-shaped antibody have and what is the significance of this?
A typical Y-shaped antibody has two antigen-binding sites, allowing it to bind to more than one antigen at the same time, which can lead to agglutination of pathogens.
Define plasma cell.
A plasma cell is a type of B-lymphocyte that produces and secretes large quantities of specific antibodies during the primary immune response.
Define memory cell.
A memory cell is a long-lived B-lymphocyte that remains in the blood and enables the secondary immune response to a previously encountered antigen.
What is the main difference between the primary and secondary immune response?
The secondary immune response is quicker and produces more antibodies than the primary immune response, due to the presence of memory cells.
True or False?
Plasma cells are long-lived and provide lasting immunity.
False.
Plasma cells are short-lived and do not provide lasting immunity; memory cells provide long-term immunity.
Which type of cell is responsible for producing antibodies in the immune response?
It is the plasma cells (derived from B-lymphocytes) that produce antibodies.
During the primary immune response, cells secrete specific antibodies into the blood, but are short-lived.
During the primary immune response, plasma cells secrete specific antibodies into the blood, but are short-lived.
Memory cells enable a immune response, which is faster and produces more antibodies than the primary response.
Memory cells enable a secondary immune response, which is faster and produces more antibodies than the primary response.
The primary immune response is slow because it takes time for clonal selection, of lymphocytes, and antibody production.
The primary immune response is slow because it takes time for clonal selection, mitosis of lymphocytes, and antibody production.
Why are some diseases, like the common cold, not prevented by immunological memory?
Diseases such as the common cold are caused by viruses with antigenic variability, so each strain has different antigens and the immune system must carry out the primary immune response each time before immunity is achieved.
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