What defensive mechanisms does our body have against pathogens?
Preventing the entry of pathogens by a variety of physical and chemical defences, such as the skin, mucous membranes, tears (containing the enzyme lysozyme, which destroys bacteria) and saliva
Inflammation (swelling and heating) of the region invaded by the pathogen, a process known as a non-specific inflammatory response
Recognising ‘foreign’ cells and targeting any pathogenic cells, a process known as a specific immune response
How do our cells recognise foreign cells
specific molecules found on the surface of cells (and viral particles) that enable them to be identified by the body
These molecules are usually proteins
They are often proteins that are part of the phospholipid bilayer, such as glycoproteins
What are the surface proteins found on to allow the body to recognise its own cells?
pathogenic cells
abnormal body cells - cancerous
toxins
cells from other individuals of the samespecies
What are antigens?
protein that are used by the body to identifycells
What is an example of the importance of antigens in defending against pathogens?
white blood cells, phagocytes have surface proteins that act as receptors and bind to the protein, antigens
Enables pathogens to be engulfed and digested
the antigens are then presented on the cellsurface of the phagocyte - antigen presenting cell
this then recruits other cells of the immune system leading to a specificimmuneresponse
What are the different antigens?
self antigens - do not stimulate an immuneresponse
non-self antigens - stimulate an immune response
What is antigen variability?
the antigens present on their surface changefrequently due to genetic mutations
Why does antigen variability pose a problem for the immune system?
lymphocytes and memory cells produce a specific immune response
the surface receptors on lymphocytes and memory cells are complementary in shape to only one antigen
when the antigen changes the lymphocytes and memory cells can nolongerbind
there is no secondaryimmuneresponse, so get infected and suffer from disease again
What are phagocytes?
white blood cells
What are the two types of phagocytes?
neutrophils
macrophages
What is the role of phagocytes?
recognise and engulf pathogens - phagocytosis
non-specific immune response
What is the process of phagocytosis?
pathogens release chemicals that attractpathogens
phagocytes move towards pathogen they can be identified due to present of pathogenicantigens
phagocytesattaches to the pathogen by binding to its antigens
phagocyte engulfs the pathogen within a phagocytic vacuole - endocytosis
forms a phagosome when neutrophil engulfs it
phagosome fuses with lysosome to form phagolysosome
lysosome release digestive enzymelysozymes to digest the pathogen
What are the two types of lymphocytes?
T-lymphocytes
B-lymphocytes
What do mature cells have?
specific cell surface receptors called T cell receptors - these have a similar structure to antibodies and are specific to one pathogen
What happens when t-lymphocytes are activated?
activated when they encounter their specific antigen
these activated t-lymphocytes divide by mitosis into either helper t cells or cytotoxic t cells
What is the role of t helper cells?
assist other white blood cells in the immune response
they release cytokines which stimulate: maturation of b-lymphocytes into antibody-secreting plasma cells, production of memory B cells, activation of cytotoxic t cels
What is the role of cytotoxic t cells?
patrol the body in search of antigen-presenting body cells
attach to the foreign antigens on the cell surface membranes of infected cells and secrete toxic substances that kill infected body cells
secrete perforins which create pores in the cellsurfacemembrane of infected cells allowing toxins to enter
What happens when B-cells have the correct cell surface receptors?
bind to the antigens - clonal selection
the b-cells divide repeatedly by mitosis - clonalexpansion differentiate into plasma cells and memory cells
What is the primary immune response?
small numbers of b-lymphocytes with receptors complementary to that antigen are stimulated to divide by mitosis
as they divide by mitosis, clonal expansion. large numbers of identical b-cells produced
some become plasma cells that secrete lots of antibody molecules - shortlived
other b-cells become memory cells that are longlasting and remain in the blood
Explain the structure of antibodies?
quarternary structure
two 'heavy' polypeptide chains bonded by dilsulfidebonds to two 'light' chains
each polypeptide has a constant and variable region
at the end of the variable region is a site called the antigen-binding site
'hinge region' where the disulfide bonds join the 'heavy' chains gives flexibility
What happens when an antigen and antibody are complementary?
the molecular structures fit into each other
it binds to one of the antigens
forming an antigen-antibodycomplex
What is agglutination?
pathogens become clumped together
each antibody has two binding sites
meaning they can bind to more than one bacteria at the same time
What is the secondary immune response?
same antigen is found in body
memory cells recognise the antigen and divide very quickly and differentiate into plasma cells
response is veryquick - infection can be destroyed and removed
What is a vaccine?
A vaccine is a suspension of antigens that are intentionally put into the body to induce artificial active immunity
How are vaccines administered and what do they produce
either by injection or orally
produce long-term immunity as they cause memory cells to be created
What are positives of vaccinations?
highly effective as they give lifetime protection
generally harmless as they do not cause the disease
What are negatives of vaccines?
poorresponse - cannot produce the antibodies
antigenic variation - variation causes the vaccine not to trigger the immuneresponse
What is herd immunity?
when a sufficiently large proportion of the population has been vaccinated making it hard for a pathogen to spread in a population
What is active immunity?
antigen enters the body triggering a specificimmuneresponse - naturally acquired through exposure to microbes
What is passive immunity?
acquired without an immune response - antibodies are not produced
What is artificial passive immunity?
occurs when people are given an injection or transfusion of the antibodies
What is natural passive immunity?
foetus receive antibodies across the placenta from their mothers
How is HIV transmitted?
sexual intercourse
blooddonation
sharing of needles
from mother to child across placenta
What is the structure of HIV?
two RNA strands
proteins - include enzyme reverse transcriptase
protein coat - capsid
viral envelope - lipid bilayer and glycoproteins
attachment proteins
How does HIV replicate?
viral RNA enters the cell
reverse transcriptase enzymes produce a DNA copy of viral RNA
DNA copy is inserted into chromosome of the cell
each time the cell divides it copies the viral DNA
How is AIDS caused?
virus reduces the number of T helper cells
B cells are no longer activated
no antibodies are produced
decreases bodys ability to fight off infections leading to AIDS
Why can't antibiotics kill viruses?
viruses are acellular, non-living. Under go no metabollic reactions
What can monoclonal antibodies be used for?
pregnancy tests
diagnosing HIV
detecting the presence of pathogens
detecting cancer cells
How can monoclonal antibodies be used to detect HIV?
HIV antigen is attached to a test plate
the blood sample being tested is passed over the test plate, if HIV antibodies are present they bind to antigen, the plate is then washed
a monoclonal antibody is then passed over the plate, it's antigen is the HIV antibody and will bind to it if it is present. Monoclonal antibody is attached to an enzyme
The enzyme catalyses a colourchange, the more intense the colour the more HIV antibody present
What are ethical issues of monoclonal antibodies - animals?
all vaccines are tested on animals - animal testing is unethical in some cultures
animal-based substances are sometimes used in production of vaccines