topic 2C: cells and the immune system

Question 1

antigen definition

Answer 1

antigens are specific molecules (proteins, glycoprotien or glycolipid) found on the surface of all cells, where these molecules are recognised as foreign by the immune system, they stimulate an immune response leading to the production of antibodies

Question 2

how are cells identified by the immune system?

Answer 2

each type of cell has specific molecules on its surface (cell surface membrane/ cell wall), which are often proteins that have a specific tertiary structure, or glycoproteins/ glycolipids

Question 3

what types of cells and molecules can the immune system identify?

Answer 3

-pathogens (organisms causing disease) e.g. bacteria, viruses, fungi - all pathogens have a specific antigen on their surface, identified as foreign by immune system cells, which then respond to destroy the pathogen

-cells from other organisms of the same species (e.g. organ transplant, blood transfusion) - cells have antigens different to your own triggering an immune response leading to rejection of transplanted organs

-abnormal body cells e.g. tumour cells or cancer/ virus-infected cells - abnormal antigens on surface, triggers immune response

-toxins (poisonous molecules) - produced by bacteria, immune system respond to toxins as well as the pathogens that release them

Question 4

antigenic variation

Answer 4

-some pathogens have many different strains and antigens on the surface of each strain are different, as they change frequently due to genetic mutations

-the DNA in a PATHOGEN may MUTATE frequently - if a mutation occurs in a gene that leads to a difference sequence of DNA, that codes for the antigen (protein)

-a DIFFERENT SEQUENCE OF AMINO ACIDS is coded for, which changes the PRIMARY STRUCTURE of the antigen (protein)

-this alters the TERTIARY STRUCTURE of the antigen (protein) as bonds form in different places - causing it to change, resulting antigens having different 3D shapes

-as the antigens are a new shape, the previous natural immunity to this pathogen is no longer effective, as memory cells are specific to only one type of antigen

Question 5

antigenic variability in a vaccine

Answer 5

-the pathogen may MUTATE frequently, so that it’s ANTIGENS CHANGE SUDDENLY rather than gradually

-this means vaccines suddenly become INEFFECTIVE because the new antigens on the pathogen are no long recognised by the immune system

-therefore the immune system does not produce the antibodies to destroy the pathogen

Question 6

describe phagocytosis of pathogens1