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A Level Biology Y1 > Cell Recognition and the Immune System > Flashcards

Cell Recognition and the Immune System Flashcards

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1
Q

what is a pathogen

A
  • a microorganism that causes disease
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2
Q

what are the types of infectious pathogens

A
  • bacteria
  • viruses
  • fungi
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3
Q

what is it called when a pathogen is transferred from one person to another

A
  • transmission
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4
Q

viruses are … (2)

A
  • acellular
  • non-living
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5
Q

what do viruses not have (4)

A
  • no nucleus
  • no organelles
  • no cell-surface membrane
  • no cytoplasm
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6
Q

what will a typical virus always contain

A
  • genetic material (DNA/RNA)
  • a capsid (made of protein)
  • attachment proteins on the outside
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7
Q

where can viruses replicate

A
  • inside living host cells
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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
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9
Q

where can viruses replicate

A
  • inside living host cells
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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
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11
Q

examples of defence mechanisms that are slower and specific to each pathogen

A
  • cell mediated response ( T lymphocytes)
  • humoral response ( B lymphocytes)
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12
Q

what is phagocytosis

A
  • the engulfment and destruction of microorganisms by phagocytic white blood cells
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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
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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
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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
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16
Q

what are antigens

A

proteins or glycoproteins that appear foreign to the individual organism exposed to them

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17
Q

what do antigens stimulate

A
  • antigens stimulate the production of antibodies by B lymphocytes
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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
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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
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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
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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
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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
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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
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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
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25
Q

where are antibodies found (3)

A
  • blood plasma
  • tissue fluid
  • breast milk
26
Q

what is the basic structure of an antibody

A

four polypeptide chains arranged in a Y shape

  • two heavy chains
  • two light chains
  • joined together by disulfide bonds
27
Q

what does each polypeptide chain of an antibody consist of + describe them

A

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
Q

what do the variable regions of the heavy and light chains form in antibodies + describe it

A

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
Q

what is agglutination

A

the clumping together of cells possessing the antigen against which specific antibodies (agglutinins) react

30
Q

which processes are stimulated due to the formation of an antibody-antigen complex

A

destruction of pathogen by :

  • agglutination of antigens
  • stimulation of phagocytosis
31
Q

how does agglutination work

A
  • 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
Q

what happens when someone receives the wrong blood group

A
  • agglutination of donor red blood cells
33
Q

what are T cells

A
  • 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
Q

how does the cellular response work

A
  • 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
Q

what do the cloned T cells do (3)

A
  • 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
Q

how is phagocytosis stimulated

A
  • 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
Q

what are the two main types of immunity

A
  • passive immunity
  • active immunity
38
Q

what is passive immunity

A

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
Q

what is active immunity

A

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
Q

what is a vaccine

A
  • an injection containing a dead or attenuated pathogen or just the antigens
41
Q

how does a vaccine work

A

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
Q

what is a booster injection

A

additional dose of vaccine to boost production of antibodies to level to maintain desired immunity

43
Q

how does herd immunity work

A

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
Q

what is AIDS caused by

A

human immunodeficiency virus (HIV)

45
Q

what is HIV

A

a retrovirus containing RNA and the enzyme reverse transcriptase is which produces DNA in the host cell using RNA as a template

46
Q

what are the RNA and enzymes in HIV surrounded by

A
  • a capsid (protein coat)
47
Q

what is the capsid in HIV surrounded by

A
  • a lipid envelope which contains glycoprotein ‘spikes’ which enable it to attach to its host cell (helper T cells)
48
Q

how is HIV transmitted (4)

A

-sexual transmission

-blood products/transfusions

-sharing of needles

-mother to baby (via placenta, breast milk or during childbirth)

49
Q

Describe the replication of HIV (extended answer)

A

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
Q

what does the indirect ELISA test measure

A
  • amount of antibodies which determines if an individual has antibodies against a pathogen indicating a previous or current infection
50
Q

can HIV be cured

A

no , but it can be controlled

  • controlled by anti-viral medication
50
Q

why is untreated HIV dangerous

A
  • 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
Q

phases of HIV to AIDS (4)

A
  • 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
Q

why don’t antibiotics work against viruses

A

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
Q

how are monoclonal antibodies used for medical diagnosis

A
  • 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
Q

how are monoclonal antibodies used to target medication to specific cell types

A
  • 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
Q

what are monoclonal antibodies

A

Identical antibodies that have the same antigen binding site produced from a single group of genetically identical B-cells (plasma cells)

52
Q

two uses of monoclonal antibodies

A
  • to target medication to specific cell types
  • for medical diagnosis
52
Q

what does the direct ELISA test measure

A
  • amount of antigens which determines if a pathogen is present in a sample
53
Q

Describe how to carry out a Direct ELISA Test

A
  • 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
Q

Describe how to carry out a Indirect ELISA Test

A
  • 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

A Level Biology Y1 (8 decks)

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