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AQA Biology A level > Cell recognition and the immune system > Flashcards

Cell recognition and the immune system Flashcards

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1
Q

What is the definition of an antigen?

A

Usually proteins on the surface of cells which generate an immune response by lymphocyte cells when detected in the body

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2
Q

What do antigens identify?

A

Pathogens
Cells from other organisms of the same species
Abnormal body cells
Toxins

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3
Q

What are the non-specific defence mechanisms?

+ What does non-specific mean?

A

Non-specific: response is immediate and the same for all pathogens

Physical barrier -> skin
Phagocytosis

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4
Q

What are the specific defence mechanisms?

+ What does specific mean?

A

Specific: response is slower and specific to each pathogen

Cell mediated response -> T lymphocytes
Humoral response -> B lymphocytes

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5
Q

How does the body distinguish between own and foreign cells?

A

Specific molecules on cell’s surface allow lymphocytes to identify self/non-self cells

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6
Q

What are the two types of white blood cell?

A

Phagocytes

Lymphocytes

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7
Q

What is the process of phagocytosis?

A
  1. Phagocyte is attracted to pathogen by its chemical products + moves towards the pathogen
  2. Phagocyte’s receptors attach to chemicals on pathogen’s surface
  3. Lysosomes in phagocytes move towards phagosome formed by the engulfed pathogen
  4. Lysosomes release lysozymes (enzymes) into phagosome which hydrolyses the bacterium
  5. Phagocyte absorbs the hydrolysis produces of bacterium
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8
Q

What are the two types of lymphocytes? + what are they associated with?

A

B lymphocytes -> B cells (humoral immunity)

T lymphocytes -> T cells (cell mediated immunity)

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9
Q

What are antigen presenting cells? + some examples

A

Cells that display foreign antigens on their surface -> they can present antigens of other cells

Phagocytes, abnormal self cells, infected body cells

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10
Q

What do T cells respond to?

A

Only respond to antigen presenting cells and not antigens detached from cells (in blood)

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11
Q

What is the cell mediated/cellular response?

A
  1. Pathogens invade body cells/taken in by phagocytosis
  2. Phagocytes present antigens from pathogen
  3. T helper cell’s receptors fit particular antigen
  4. Attachment between T helper cells and antigens causes T cell to divide rapidly by mitosis and form clones
  5. The cloned T cells:
    - Stimulate B cells to divide
    - Activate cytotoxic T cells
    - Stimulate phagocytes to engulf pathogens in phagocytosis
    - Form memory cells
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12
Q

How do cytotoxic T cells kill infected cells?

A

Produce a protein called perforin which form holes in cell surface membrane, making it permeable to all substances so cell dies

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13
Q

What is the humoral response?

A
  1. Clonal selection->
    - Specific B cell binds to an antigen presenting cell and is stimulated by helper T cells which release cytokines
    - Divides rapidly by mitosis to form clones (clonal expansion)
  2. Some clones become B plasma cells for the primary response - secrete large amount of monoclonal antibody in the blood
  3. Some become B memory cells for the secondary response
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14
Q

What is the primary response? -> role of plasma cells

A

Antibodies are produced slower and at a lower concentration because:
-not as many B cells are available to produce antibodies
-T helper cells need to activate B plasma cells to make antibodies which takes time
Therefore the person will experience symptoms

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15
Q

What is the secondary response? -> role of memory cells

A

Produces antibodies faster and at a higher concentration because:

  • B and T memory cells present
  • B memory cells undergo mitosis more quickly / quicker clonal selection
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16
Q

What is an antibody?

A

Proteins with specific binding sites synthesised by B cells which produce a specific antibody when the body is infected by non-self material

Antibody binding sites are complimentary to a specific antigen to form an antigen-antibody complex

17
Q

What is the structure of an antibody?

A

Quaternary structure: 4 polypeptide chains-> two heavy and two light
Variable region: binding site which is different for each antibody -> consists of a sequence of amino acids which forms a specific 3D shape to bind to a specific antigen
Constant region: same for all antibodies

18
Q

How do antibodies lead to the destruction of antigens?

A
  • Cause agglutination (clumps of cells) so it is easier for phagocytes to locate them and they are less spread out in the body
  • Stimulate phagocytosis to engulf pathogens
19
Q

What are monoclonal antibodies?

A

Antibodies produce by the identical offspring of a single, cloned antibody producing cell

20
Q

What are the uses of monoclonal antibodies?

A

-Target specific substances and cells e.g cancer

21
Q

How do monoclonal antibodies treat cancer?

A
  • Monoclonal antibodies are produced which are specific to antigens on cancer cells
  • These are given to patients and attach themselves to the receptors on cancer cells
  • They attach to surface of cancer cells and block the chemical signals that cause the uncontrolled cell growth
22
Q

How does a pregnancy test work? (to show a positive result)

A

Urine is passed onto the tip of the pregnancy test and it passes through the reaction zone. HCG binds to the mobile antibodies. HCG travels to the results zones and binds to the immobilised antibodies that are specific to HCG. Antibodies which are not specific to HCG do not attach but bind to the immobilised antibodies in the control window. A positive result will show a blue line in both the control window and results window.

23
Q

What are the ethical issues with monoclonal antibodies?

A

Strengths

  • used in pregnancy testing
  • used to treat diseases to save lives

Problems

  • cancer is deliberately induced into mice
  • some death associated with the use of monoclonal antibodies
24
Q

How are monoclonal antibodies formed?

A 
A mouse is immunised by an antigen to stimulate antibody production 
Plasma cells (antibody forming cells) are isolated from  the mouse's lymphonodes 
These cells are fused to myeloma cells (tumour) grown in culture which forms a hybridoma cell
Each hybridoma forms large quantities of identical antibodies -> produces a population of cells
25
Q

What is passive immunity?

A

Antibodies which are introduces into the body
Pathogen does not enter the body so plasma cells/memory cells are not made
No long term immunity -> short term
Body is not actively producing humeral response
NATURAL: antibodies from mother in breast milk
ARTIFICIAL: antibodies from medicine

26
Q

What is active immunity?

A

Immunity created by your own immune system after experiencing exposure to pathogen/its antigens
NATURAL: antibodies produced after an infection
ARTIFICIAL: antibodies produced in response to a vaccination

27
Q

What is herd immunity?

A

Large proportion of the population has been vaccinated making it difficult for the pathogen to spread
-> makes it more difficult to come into contact with an infected person

Important because not everyone can be vaccinated -> e.g babies and young children who do not have fully developed immune systems

28
Q

What is antigen variability?

A

Pathogen’s DNA mutates frequency
If a mutation occurs the shape of the antigen will change
Therefore previous immunity to the pathogen will not be effective as memory cells will only have memory of the old shape

29
Q

What are the ethics of using vaccines?

A
  • Religion
  • Vaccines are tested on animals
  • Side effects
  • Morality
  • Herd immunity - people believe that they don’t need the vaccine if everyone else has it
30
Q

What is the structure of HIV?

A
  • Lipid envelope on outside
  • Attachment proteins
  • Capsid - protein layer enclosing two single strands of RNA and enzymes (including reverse transcriptase which allows the formation of DNA from RNA)
  • Matrix next to lipid envelope
31
Q

How does HIV replicate?

A
  1. Protein on HIV binds to a CD4 protein
  2. Protein capsid fuses with cell surface membrane, RNA and enzymes of HIV enter helper T cell
  3. HIV reverse transcriptase converts viruses RNA to DNA
  4. DNA is moved into helper T cell’s nucleus into DNA
  5. HIV DNA in nucleus produces messenger RNA usingg enzymes -> mRNA contains instructions used to make new viral proteins and RNA to go into new HIV
  6. mRNA passes through nuclear pore and creates new HIV particles using protein synthesis
  7. HIV particles break from the helper T cells with a piece of cell membrane to create their lipid envelope
32
Q

How does HIV cause AIDS?

A

Infects and kills T cells as it multiplies quickly so T cells cannot stimulate cytotoxic T cells, B cells and phagocytes so there is an impaired immune response (no destruction of pathogens through phagocytosis)
Immune system becomes weaker so it is more susceptible to infections and diseases that aren’t usually deadly are.

33
Q

Why are antibiotics ineffective against viruses?

A

Antibiotics can’t enter human cells but viruses exist in host cells
Viruses don’t have their own metabolic reactions which antibodies target

34
Q

What are ELISA tests used for?

A

To determine if a patient has:
antibodies to a certain antigen
antigen to a certain antibody

Used to diagnose diseases/allergies such as HIV or lactose intolerance

AQA Biology A level (13 decks)

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