Cell Recognition and the Immune System Flashcards
1
Q
what is a pathogen
A
- a microorganism that causes disease
2
Q
what are the types of infectious pathogens
A
- bacteria
- viruses
- fungi
3
Q
what is it called when a pathogen is transferred from one person to another
A
- transmission
4
Q
viruses are … (2)
A
- acellular
- non-living
5
Q
what do viruses not have (4)
A
- no nucleus
- no organelles
- no cell-surface membrane
- no cytoplasm
6
Q
what will a typical virus always contain
A
- genetic material (DNA/RNA)
- a capsid (made of protein)
- attachment proteins on the outside
7
Q
where can viruses replicate
A
- inside living host cells
8
Q
how do viruses replicate
A
- attachment glyco/proteins on the virus which are complementary to the receptors on the cell surface membrane of host cells are used to attach to a specific host cell
- most viruses then inject their nucleic acid (DNA/RNA) into the host cells
- the genetic material is used to code for more virus particles which are produced using the organelles of the host cell
- this involves producing copies of the viral nucleic acids and proteins to form complete viruses which are often released by lysis of the cell
9
Q
where can viruses replicate
A
- inside living host cells
10
Q
what type of defence mechanism is immediate and the same for all pathogens + examples
A
non-specific
- physical barriers ( skin, stomach acid , mucus and cilia)
- phagocytosis
11
Q
examples of defence mechanisms that are slower and specific to each pathogen
A
- cell mediated response ( T lymphocytes)
- humoral response ( B lymphocytes)
12
Q
what is phagocytosis
A
- the engulfment and destruction of microorganisms by phagocytic white blood cells
13
Q
Describe the process of phagocytosis (extended answer)
A
- phagocyte detects microbes by the chemicals they give off (chemotaxis)
- the microbe is engulfed by the phagocyte membrane
- phagosome (phagocytic vesicle) forms and fuses with a lysosome which contains hydrolytic enzymes
- the microbe is hydrolysed and the indigestible matter is discharged
14
Q
what is an antigen presenting cell
A
- when a phagocyte removes the antigens from the pathogen they destroy and present the antigens on their cell surface membrane to T cells
15
Q
how do phagocytes prevent disease spread to other parts of the body
A
- they destroy microorganisms that enter the blood and other tissues
16
Q
what are antigens
A
proteins or glycoproteins that appear foreign to the individual organism exposed to them
17
Q
what do antigens stimulate
A
- antigens stimulate the production of antibodies by B lymphocytes
18
Q
where could antigens be present (4)
A
- on the surface of a pathogen
- on the cell surface membrane of other organisms of the same species
- abnormal body cells e.g. cancer cells
- as a toxin e.g. a free molecule often produced by a pathogen
19
Q
describe the humoral response ( B cells) work
A
- the body has a lot of different types of B lymphocytes which each are capable to produce a different specific antibody
- these b lymphocytes secrete small amounts of their specific antibody onto their cell surface membrane
- a specific antigen may attach to the complementary antibody on B lymphocytes
- these B cells are stimulated to divide by mitosis resulting in a large population of identical plasma cells , this is called clonal selection
- helper T cells have to activate the B-calls to divide
- plasma cells will all produce the specific antibody and secrete it into the blood plasma
20
Q
how is the the destruction of a pathogen/antigen stimulated
A
- the antibodies secreted by the b cells bind and form an antibody-antigen complex which stimulates the destruction of the antigen/pathogen
21
Q
how do b cells provide immunity to a specific pathogen
A
- some of the b cells are stimulated to divide and develop into memory b cells which stay in the blood for a long time
22
Q
why does the primary response to a pathogen normally result in symptom but the secondary response normally doesn’t
A
- the first response is relatively slow as it may require several days to produce a substantial concentration of antibodies
- during this time, the pathogens will reproduce causing disease symptoms to arise
- if the same pathogen is encountered again by a memory b cell, the memory b cells will divide and develop into plasma cells
- these plasma cells secrete antibodies more quickly and at a higher concentration than before and so pathogens are destroyed before symptoms develop
23
Q
what does antigenic variation mean?
A
- the ability of pathogens like influenza, to change their surface antigen through mutation meaning that the memory b cells will not recognise them and the antibodies produced are no longer complementary
24
Q
what happens when plasma cells are exposed to a specific antigen
A
- they secrete their specific antibody molecules into the blood plasma to destroy or neutralise the antigen and the pathogen
25
where are antibodies found (3)
- blood plasma
- tissue fluid
- breast milk
26
what is the basic structure of an antibody
four polypeptide chains arranged in a Y shape
- two heavy chains
- two light chains
- joined together by disulfide bonds
27
what does each polypeptide chain of an antibody consist of + describe them
constant region
- where the sequence of amino acids is the same in all molecules of the same type of antibody
variable region
- where the amino acid sequence varies between different antibody molecules which are specific to different antigens
28
what do the variable regions of the heavy and light chains form in antibodies + describe it
antigen binding sites
- each site has a specific tertiary structure complementary to the structure of the antigen molecule to which they attach to form an antigen-antibody complex
29
what is agglutination
the clumping together of cells possessing the antigen against which specific antibodies (agglutinins) react
30
which processes are stimulated due to the formation of an antibody-antigen complex
destruction of pathogen by :
- agglutination of antigens
- stimulation of phagocytosis
31
how does agglutination work
- an antibody molecule can use its two antigen binding sites to attach to the same antigen on two different cells
- this joins the cells together and as more antibody molecules attach, more cells are linked together to form an agglutinated mass which are then more easily destroyed
32
what happens when someone receives the wrong blood group
- agglutination of donor red blood cells
33
what are T cells
- lymphocytes that have receptors on their cell surface membrane which bind to specific antigens
- the receptors on each T cell are complementary to a single specific antigen
34
how does the cellular response work
- a phagocytes engulfs a pathogen, removes its antigens and embeds it in their cell-surface membrane becoming an antigen presenting cell
- the helper T cell with the complementary protein receptor binds to the antigen and is stimulated to divide by mitosis and form clones of genetically identical T cells with the same receptor
35
what do the cloned T cells do (3)
- activate cytotoxic T cells which attach to the specific antigen on the pathogen and secrete chemicals (perforin) to destroy it
- develop into more helper t cells which stimulate b lymphocytes to divide into plasma cells and secrete antibodies
- develop into memory T cells that remain in the blood to produce a quicker secondary response if exposed to the same antigen/pathogen
36
how is phagocytosis stimulated
- antibody binds to the antigen on the surface of the pathogen
- phagocytes have receptors that recognise the antibody and enable them to bind to it and engulf and destroy the pathogen
37
what are the two main types of immunity
- passive immunity
- active immunity
38
what is passive immunity
short term immunity using antibodies produced outside the body
- natural passive - antibodies are obtained across the placenta or through breast milk
- artificial passive - preformed specific antibodies are injected usually after exposure to very dangerous pathogens e.g.venom
39
what is active immunity
long term immunity due to exposure to antigen which stimulates the production of antibodies and memory B cells
- natural active - from being infected and exposed to the specific antigen resulting in memory cells being formed
- artificial active - from vaccination after which the persons immune system produces its own antibodies and memory cells
40
what is a vaccine
- an injection containing a dead or attenuated pathogen or just the antigens
41
how does a vaccine work
the injection stimulates an immune response with the production of plasma cells which release specific antibodies, memory B cells and memory T cells which provide long-term immunity
42
what is a booster injection
additional dose of vaccine to boost production of antibodies to level to maintain desired immunity
43
how does herd immunity work
if a high proportion of individuals are immune to an infection then the whole population will be protected as there is low probability of an infected person encountering a person without immunity
44
what is AIDS caused by
human immunodeficiency virus (HIV)
45
what is HIV
a retrovirus containing RNA and the enzyme reverse transcriptase is which produces DNA in the host cell using RNA as a template
46
what are the RNA and enzymes in HIV surrounded by
- a capsid (protein coat)
47
what is the capsid in HIV surrounded by
- a lipid envelope which contains glycoprotein 'spikes' which enable it to attach to its host cell (helper T cells)
48
how is HIV transmitted (4)
-sexual transmission
-blood products/transfusions
-sharing of needles
-mother to baby (via placenta, breast milk or during childbirth)
49
Describe the replication of HIV (extended answer)
1 - virus attaches using their glycoprotein spikes which are complementary to specific protein receptor sites on the helper T cells
2 - lipid envelope fuses with the cell-surface membrane and viral RNA and reverse transcriptase are released into the helper T cell
3 - in the T cell,the enzyme reverse transcriptase uses the viral RNA as a template to make viral DNA
4 - viral DNA enters the nucleus and attaches to the host DNA
5 - viral DNA replicates with the host DNA (viral DNA may remain inactive for long time
6 - when activated the viral DNA controls the synthesis of viral RNA
7 - viral RNA codes for the synthesis of viral proteins and more viral RNA
8 - HIV particles are assembled and the viral lipid envelope is formed from the host cell membrane and the helper T cell is destroyed as the viruses are released
9 - new virus particles infect other helper T cells or may be transmitted to another person
50
what does the indirect ELISA test measure
- amount of antibodies which determines if an individual has antibodies against a pathogen indicating a previous or current infection
50
can HIV be cured
no , but it can be controlled
- controlled by anti-viral medication
50
why is untreated HIV dangerous
- if untreated, viral replication destroys host cells drastically reducing the amount of helper T cells
- less T cells = less activation of B lymphocytes and coordination of immune response
- immune system collapses = infections/tumours that lead to death
50
phases of HIV to AIDS (4)
- initial infection
body produces HIV antibodies and there may be a short flu-like illness
- antibody-positive phase (HIV positive phase)
the period between infection and the onset of clinical signs
- AIDS related complex
t helper cell number decrease and so person gets a variety of microbial infections
- AIDS
t helper cell number so low = person gets specific cancer/pneumonia
51
why don't antibiotics work against viruses
Bacteria cells are prokaryotic, whereas viruses just insert their DNA into a host eukaryotic cell. Antibiotics target the cell wall or metabolic processes, and viruses don't have these
51
how are monoclonal antibodies used for medical diagnosis
- to detect the presence of specific antigens in body fluids to detect if a person is infected with a particular disease
- to detect the presence of specific antibodies produced by a person against a particular antigen ( i.e pathogen)
51
how are monoclonal antibodies used to target medication to specific cell types
- by attaching a therapeutic drug to an antibody
e.g. cancer cells display different antigens to healthy cells and so can be targeted by monoclonal antibodies with a toxic drug attached killing the cancer cells and leaving the healthy cells unaffected
51
what are monoclonal antibodies
Identical antibodies that have the same antigen binding site produced from a single group of genetically identical B-cells (plasma cells)
52
two uses of monoclonal antibodies
- to target medication to specific cell types
- for medical diagnosis
52
what does the direct ELISA test measure
- amount of antigens which determines if a pathogen is present in a sample
53
Describe how to carry out a Direct ELISA Test
- plastic tray divided into wells. Each well has a specific monoclonal antibody (produced for the antigen about to be detected) bound to well
-the sample to be tested (e.g. blood, urine) is added to the well. If the specific antigen is present, it will bind to the monoclonal antibodies forming an antibody-antigen complex
- a second monoclonal antibody ,specific to the same antigen, with an enzyme attached to it is added.
- the well is washed to remove any unbound second antibodies
- a substrate for the enzyme is then added and if the enzyme is still present in the well it will convert the colourless substrate into a coloured product
54
Describe how to carry out a Indirect ELISA Test
- specific antigen bound to the well
- the sample to be tested is added and if the specific antibody is present, it will bind to the antigen creating an antibody-antigen complex
- a second monoclonal antibody specific to the antibody being tested for is added. The second antibody has an enzyme attached to it
- the well is washed to remove any unbound second antibodies
- a substrate for the enzyme is then added
- if the enzyme is still present in the well it will convert the colourless substrate into a coloured product
