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biology paper 1 > 3.2.4 cell recognition and immune system > Flashcards

3.2.4 cell recognition and immune system Flashcards

1
Q

what are the five defence mechanisms of the body?

A
  1. ciliated epithelia in airways = mucus (produced by goblet cells) traps dust and pathogens
    cilia beat upwards to remove mucus
  2. hydrochloric acid in stomach = low pH so most of pathogens enzymes denature
  3. skin = physical covering
  4. blood clotting
  5. white blood cells (leucocytes) = recognise pathogens by the distinct antigens that cover the surfaces
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2
Q

what are pathogens?

A

disease-causing organisms

do not always get ill from pathogens due to built up immunity

people with a weakened immunity are more vulnerable to pathogens

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3
Q

what is immunity?

A

ability when body’s defence mechanisms overcome a specific pathogen

when it meets that pathogen again, the body is better prepared and destroys it before it can cause any harm

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4
Q

what are non specific defence mechanisms?

A

do not distinguish between one type of pathogen and another
respond to them all in the same way

mechanisms act immediately

phagocytosis - engulfing the pathogen

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5
Q

what are specific defence mechanisms?

A

specific to each pathogen

responses are slower but provide long lasting immunity

eg action of b and t lymphocytes

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6
Q

what are the two response forms of specific defence mechanisms?

A
  1. cell-mediated response involving T lymphocytes
  2. humoural response involving B lymphocytes
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7
Q

what does specific defence mechanisms involve?

A

involve a type of white blood cell called a lymphocyte

smaller than phagocytes

larger nucleus that fills most of the space in the cell

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8
Q

how do lymphocytes recognise self and non self cells?

A

lymphocytes must distinguish the body’s own cells and chemicals (self) from those that are foreign (non-self)

each cell has molecules on its surface that identifies it = antigen

usually, proteins which have enormous and specific tertiary structure

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9
Q

how do antigens allow the immune system to identify self and non self cells?

A
  1. pathogens
  2. non-self material (eg transport)
  3. toxin produced by bacteria
  4. abnormal body cells eg cancer cells
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10
Q

what is an antigen?

A

any part of an organism or substance that is recognised as non-self by the immune system and triggers an immune response eg production of antibodies

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11
Q

how are foreign cells recognised?

A

10 million different types of lymphocytes in our bodies

high probability that when a pathogen enters the body, one lymphocyte will have a protein on its surface
lymphocyte will then recognise the pathogen

when infection occurs, this specific type of lymphocyte is stimulated to build up its numbers to a level where it can be effective in destroying the pathogen (clonal selection)
therefore this is a timely between exposure to the pathogen and its destruction

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12
Q

how are our own cells recognised?

A

in the foetus, lymphocytes are constantly colliding with other cells, which are exclusively the body’s cells
(placenta prevents pathogens entering)

some of the lymphocytes will have receptors complementary to the body’s own cells
undergo apoptosis (programmed cell death)

remaining lymphocytes will only respond to foreign material

in adults, lymphocytes produced in the bone marrow initially encounter self-antigens
any lymphocytes that show an immune response to these self-antigens undergo programmed cell death before maturing

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13
Q

what are phagocytes?

A

WBCs produced in bone marrow

stored in the bone marrow before being distributed around the body by blood

remove dead cells and invasive micro-organisms, digesting and destroying the pathogen by phagocytosis

may travel in the blood but can squeeze out of other capillaries in tissues

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14
Q

describe the process of phagocytosis

A
  1. pathogen chemicals (chemoattractants) attract phagocytes
    phagocyte moves towards the pathogen up a concentration gradient
    CHEMOTAXIS
  2. phagocytes have receptors which bind to chemicals on the surface of the pathogen
    ATTACHMENT
  3. phagocytes plasma membrane engulfs the pathogen and traps it within a vesicle called a phagosome
    ENDOCYTOSIS
  4. lysosomes containing digestive hydrolytic enzymes (lysozymes) move towards the phagosomes and fuse with it
  5. lysozymes hydrolyse the pathogen
    KILLING + DIGESTION
  6. soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
    ingestible material is released by exocytosis
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15
Q

what is lymphocytes specific response?

A
  1. b lymphocytes = b cells
  2. t lymphocytes = t cells

long term immunity
slower in action than non-specific
only mature lymphocytes can carry out immune response

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16
Q

what are b lymphocytes?

A

remain in the bone marrow until mature
then spread throughout the body concentrating in the lymph nodes and spleen

associated with humoural immunity
antibodies in bodily fluids

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17
Q

what are t lymphocytes?

A

leave the bone marrow and collect in the thymus until mature
thymus = gland in chest below the sternum

associated with cell-mediated immunity
does not release antibodies is activated by other cells

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18
Q

how to t cells respond in cell mediated immunity?

A

t lymphocytes respond to an organisms own cells that have been invaded by non self material of a different species

only respond to antigens that are presented on a body cell

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19
Q

how do t cells distinguish non-self material from normal cells?

A

phagocytes engulf and hydrolyse pathogens and expose the pathogens antigens on their surface

body cell invaded by a virus displays the viral antigen as a distress signal on its CSM

cancer cells also present non self antigens on its CSM

transported cells have non self antigens on its CSM
ANTIGEN PRESENTING CELLS

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20
Q

what are the roles of receptors on T cells?

A

respond to specific antigens

there are a huge number of different t cells

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21
Q

what is the t cell response to infection?

A
  1. pathogens invade body cells or are taken in by phagocytes
  2. cell eg phagocyte places antigens from the pathogen on its CSM
  3. receptors on specific t helper cells fit exactly on these antigens
  4. clonal selection = activates specific t cells to divide rapidly by mitosis and form genetically identical clones
  5. cloned t cells:
    - develop into many memory cells that enable a rapid response to future infections by the same pathogen (circulate in blood and tissue fluid)
    - stimulate phagocytes to engulf pathogens by phagocytosis
    - stimulate b cells to divide
    - stimulate cytotoxic t cells to kill infected cells
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22
Q

how do cytotoxic t cells kill infected cells?

A

produce a protein called perforin that makes holes in the CSM

membrane becomes freely permeable and has no control over what passes in and out

cell dies

effective against viruses because viruses replicated inside living cells

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23
Q

what is humoral immunity?

A

involves antibodies that are soluble in blood and tissue fluid

10 million different types of b cells
each type produces a different antibody that responds to a specific antigen
antibody is displayed on its surface

antibody will be complimentary to a specific antigen on the surface of a pathogen

if specific antigen is encountered, the specific b cell divides by mitosis to form clones (clonal selection)

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24
Q

what is the b cell response to infection?

A
  1. b cells take up the complimentary antigens of an invading pathogen and present them on the cell surface
  2. activated t-helper cells (cell-mediated response) attach to the antigen on the surface of the B-cell
  3. b cell is activated and stimulated to divide by mitosis by the release of chemical messengers and cytokines by activated t helper cells
  4. cloned b cells become either
    a) plasma cells releasing monoclonal antibodies
    b) memory cells which respond to future infection
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25
Q

what are b lymphocyte plasma cells?

A

secrete antibodies directly

cells survive for only a few days but can make around 2000 antibodies every second

antibodies destroy the pathogen and any toxins it produces

plasma cells are responsible for the immediate defence of the body against infection
PRIMARY IMMUNE RESPONSE

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26
Q

what are b lymphocyte memory cells?

A

live longer than plasma cells

do not produce antibodies directly but circulate in blood and tissue fluid

when they encounter antigens, they divide rapidly and develop into plasma cells and more memory cells

long term immunity, more antibodies are produced at a faster rate then primary response
SECONDARY IMMUNE RESPONSE

27
Q

what are antibodies?

A

globular proteins with 4 polypeptide chains with specific binding sites

synthesised by b cells

have variable regions which are complimentary in shape to a specific antigen

variable region binds to specific antigens to form an antigen-antibody complex
rest of the antibody is known as the constant region

28
Q

how does the antibody leads to the destruction of antigens?

A

antibodies do not destroy antigens directly but prepare the antigen for destruction

cause agglutination of the bacterial cells. clumps of bacterial cells are formed making it easier for phagocytes to locate them

serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

29
Q

describe the variable and hinge region of antibodies

A

variable region = amino acid sequences in the antigen binding make a specific 3D shape which only binds to one type of antigen

hinge region = gives the flexibility for the antibody to bind around the antigen

30
Q

what are monoclonal antibodies?

A

they are a specific type of antibody produced by a specific clone of B cells

each foreign antigen will induce a specific B cell to multiply and form a clone of itself which will only make one type of antibody

monoclonal antibodies can be produced outside the body in labs
have considerable medical value

31
Q

what are the problems with monoclonal antibodies?

A

B cells are short lived
only divide within a living organism

in 1975 procedure was developed to produce large quantities of monoclonal antibodies outside the body

32
Q

describe the process of developing monoclonal antibodies outside the body

A
  1. mouse exposed to the antigen against which an antibody is required
  2. Mouse B cells produce a mixture of antibodies and the cells are extracted from the mouse spleen
  3. B cells don’t usually divide outside the body so they are mixed with cells from a cancer tumour
    cells are fused together using detergent to form hybridoma cells
  4. hybridoma cells are separated using a microscope and cultured to form a clone
  5. each clone is tested to see if it is producing the required antibody
    grown on a large scale and monoclonal antibodies are extracted from the growth medium
33
Q

what are the uses of monoclonal antibodies?

A
  1. treating cancer
  2. medical diagnosis eg prostate cancer
  3. pregnancy testing
  4. covid testing
34
Q

how is cancer treated through direct monoclonal antibody therapy?

A
  1. monoclonal antibodies are produced specific to antigens on cancer cells
  2. the Abs are given to the patient and attach themselves to receptors on their cancer cells
  3. this blocks the chemical signal that usually stimulates uncontrolled growth and division

ADVANTAGE: Abs are non toxic and highly specific
fewer side effects then other forms of therapy

35
Q

how is cancer treated through indirect monoclonal antibody therapy?

A
  1. a radioactive/cytotoxic drug is attached to the monoclonal Abs
  2. the Abs is given to the patient
  3. the Abs attach to the cancer cells and the drug kills them

ADVANTAGE: Abs are specific, the drugs can be used in smaller quantities rather than chemotherapy drugs

36
Q

how is an ELISA test used in medical diagnosis?

A

prostate cancer can lead to abnormally high levels of a plasma protein called psi
can be tested using an ELISA test

37
Q

what does an ELISA test consist of?

A
  1. antigen-coated well
    WASH
  2. add specific antibody to be measured
    WASH
  3. add enzyme-conjugated secondary antibody
    WASH
  4. add substrate and measure colour
38
Q

how are monoclonal antibodies used in pregnancy testing?

A

placenta secretes a hormone called human chorionic gonadotrophin (hCG)

secreted in pregnant women’s urine and added to testing strip

39
Q

what is the ethical use of monoclonal antibodies?

A
  1. production of antibodies involves the use of mice and involves deliberately cancer in them
    despite the specific guidelines drawn up to minimise suffering, some people still have reservations about using animals in this way
  2. deaths associated with the use of monoclonal antibodies with treatment of multiple sclerosis
    important that patients have full knowledge of the risks and benefits before giving permission = informed consent
  3. testing for the safety of new drugs presents certain dangers and may raise issues about the conduct of drug trials
40
Q

what does immunity mean?

A

immunity is the ability of an organism to resist infection by destroying pathogens before they cause the symptoms of the disease

41
Q

what are the 2 types of immunity?

A
  1. passive immunity
  2. active immunity
42
Q

what is passive immunity?

A

B + T cells have not been activated and the body did not produce its own antibodies

antibodies come from an outside source

antibodies don’t remain in the blood for long periods as they get broken down = short term immunity

43
Q

how does breast milk contain passive immunity?

A

newborn infants have only received some antibodies via the placenta during pregnancy which gives a low immune response at birth

colostrum = thick yellowish fluid produced by mother’s breast in first 4-5 days has high concentrations of Ab

44
Q

what is active immunity?

A

occurs during an infection (natural or artificial)

immunity is active because T and B lymphocytes are activated by antigens and the body’s own antibodies
memory cells are produced

45
Q

what are the two types of active immunity?

A
  1. natural active immunity = immune response that occurs following a natural infection
  2. artificial active immunity = immune response can also be activated by infecting antigens or taking them by mouth
    similar to vaccinations
46
Q

what is an issue with both types of immunity?

A

takes time for sufficient active B + T cells to be produced that give efficient defence

some diseases eg tetanus can kill quickly before the primary response can take place

47
Q

how are vaccinations created?

A

preparation containing antigenic material
may be:
1. a whole organism
2. a dead organism (destroyed by heat)
3. a harmless organism
4. a harmless form of toxic
5. a preparation of surface antigens

given by injection or taken orally

vaccinations mimic immunity being extremely good at protection against natural infection
memory cells are produced

48
Q

what are features of a successful vaccination programme?

A

must be available at the right cost and sufficient amounts to enable the whole population to be vaccinated

should give a few sides effects

must be able to be produced, stored and transported with ease

must be correctly administered, may need more training

better to vaccinate the vast majority of the population to create herd immunity

49
Q

why may vaccinations not eliminate a disease?

A
  1. due a defective immune system
  2. some individuals may develop the disease before their immunity is induced so they might harbour the pathogen and infect others
  3. malnutrition = do not have enough protein to make antibodies or clones of lymphocytes
  4. vaccinated with a live virus = can pass out through faeces during primary response and infect others
  5. many varieties of the disease so is impossible to develop an effective vaccine
  6. pathogen may mutate frequently, so antigens change (antigenic variability) and vaccine is ineffective
  7. individuals might have objections for religious, ethical or medical reasons
  8. some pathogens conceal themselves in cells or live out of reach
50
Q

what is antigenic variability?

A

change in antigens through mutations

influenza mutates regularly to give different antigens

vaccines suddenly become ineffective as antigens are no longer recognised by immune system, no antibodies are produced

protective immunity from vaccination is ineffective against new strain

so vaccination needs to change every year

51
Q

what is antigenic concealment?

A

pathogens can hide in the body eg inside cells or less easily reached areas

difficult to develop vaccines because there is a short time for immune response to occur before it hides

52
Q

describe the ethics of vaccinations

A
  • production of existing and new vaccines involves the use of animals. how acceptable?
  • vaccines have side effects that may sometimes cause long term harm.
  • who should vaccines be tested on? how should trials be conducted?
  • is it acceptable to trial a new vaccine with unknown health risks only on a population where targeted disease is common?
  • should vaccinations be compulsory?
  • should expensive vaccination programmes continue when a disease is nearly eradicated?
  • how can any individual health risks from vaccinations be balanced against the advantages of controlling a disease
53
Q

describe an eradication programme

A

infected people were easy to identify

vaccine easy to administer, bifurcated needle with two prongs to insert vaccine

did not infect animals so easy to break down transmission cycle

many 16-17 year olds become vaccinators and suppliers of information

54
Q

what is the structure of HIV?

A

lipid envelope on the outside with glycoproteins embedded on the outside

protein capsid encloses two single strands of RNA and the enzyme reverse transcriptase

HIV is the virus that causes AIDS
AIDS is the collection of opportunistic diseases associated with immunodeficiency caused by HIV infection

55
Q

what is HIV?

A

retrovirus and contains the enzyme reverse transcriptase which makes DNA from an RNA template

DNA then integrates within a chromosome in the host cell

HIV infects T-helper cells but also macrophages and brain cells

56
Q

how is HIV replicated?

A

HIV enters the bloodstream following infection

it binds to a protein receptor called CD4 on T helper cells and fuses with their plasma

Viral RNA and enzymes enter the host cell

Reverse transcriptase makes ds DNA from RNA and DNA is inserted unto the host DNA

viral genes may remain dormant for some time even years
once activated, they are transcribed into mRNA for production of new viral proteins and RNA for new viral genomes

new virus particles are assembled and bud out from host cell, eventually destroying it

57
Q

how is HIV transmitted?

A

sexually in semen or vaginal fluid

via contaminated blood products and transfusions

shared needles

placenta, during birth or as a result of breast feeding

the virus is unable to survive outside the body
therefore transmission is only possible by direct exchange of bodily fluids

58
Q

how does HIV cause the symptoms of AIDS?

A

once infected with HIV an individual is HIV positive

HIV destroys T-helper cells and interferes with their normal function
lowers the amount of T-helper cells than an average person

without sufficient T-helper cells, the immune system cannot stimulate B lymphocytes to produce antibodies or cytotoxic T cells to kill infected cells

the individual becomes vulnerable to opportunistic infections such as pneumonia

cancers and degenerative diseases of the brain are the most common causes of death

HIV does not kill individuals directly, secondary diseases causes death

59
Q

what are the 3 stages of HIV?

A
  1. may experience flu-like symptoms when first infected
  2. patient may appear healthy for years
  3. AIDS starts to develop, the patient becomes vulnerable to opportunistic diseases
    viral load increases, CD4 count decreases and further opportunistic diseases develop
60
Q

how is HIV tested through the ELISA test?

A
  1. The sample is immobilised on a slide
  2. antibody is added, specific to the antigen we need to detect
  3. sample is washed to remove excess antibody
  4. A second antibody is added that binds with the first antibody. the second antibody has an enzyme attached to it
  5. a colourless substrate of the enzyme is added
    enzyme changes the colourless substance into a coloured product

amount of antigen is relative to the intensity of colour that develops

61
Q

why are antibiotics ineffective against viral diseases?

A

vaccines have been problematic, because the virus mutates frequently

treatment has generally been to attack HIV with a combination of antiviral drugs, reducing the chance of resistance that inhibit reverse transcriptase
these drugs have significant side effects

public health measures are important in preventing eg condoms, needle exchange

62
Q

when was AIDS first recognised?

A

thought to have arisen as a result of transmission from immunodeficiency viruses (SIUS) from non human primates to humans in central africa

first officially designated cases were in the USA in the 1980s amongst male homosexuals

may haemophiliacs were also infected

63
Q

why is HIV/AIDS especially prevalent in sub-saharan africa?

A

heat treatment and screening blood are expensive as well as needle exchange schemes and contact tracing

antiviral drugs are too expensive for many

difficult to reach and test much of the population

myths and traditional practices may reinforce harmful behaviour involving encouraging to sleep around
may not have the power to say no or have safe sex
will not acknowledge homosexuals

lack of educations means people are ignorant of symptoms

biology paper 1 (23 decks)

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