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A Level Biology: Cell recognition and the immune system > 5.5 - Antibodies > Flashcards

5.5 - Antibodies Flashcards

1
Q

What are antibodies

A
  • proteins with specific binding sites synthesised by B cells
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2
Q

Describe how an antibody reacts with an antigen

A
  • Binds to them on the surface of the non-self material
  • each antibody has 2 identical binding sites
  • the antibody identity sites are complementary to a specific antigen
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3
Q

What makes the variety of antibodies possible

A
  • they’re made of proteins
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4
Q

Describe the structure of an antibody

A
  • made up of 4 polypeptide chains, the chains of one pair = long (called heavy chains), while the chain of the other pair = shorter (called light chains)
  • specific binding site for each antibody, fits precisely to the antigen to form: antigen-antibody complex
  • the different binding sites on each antibody is known as: variable region
  • each binding site consists of a sequence of amino acids that form the specific 3D shape that binds directly to a specific antigen
  • the rest of the antibody is known as the constant region, its the same for all antibodies. It binds to the receptors on cells such as B cells
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5
Q

How does the antibody lead to the destruction of the antigen

A

antibodies don’t destroy antigens, but prepare the antigen for destruction in a different range of ways for each antibody
- e.g.: when the antigen is a bacterial cell - antibodies assist in its destruction in 2 ways:
1) agglutination - clumps of bacterial cells are formed, making it easier for the phagocytes to locate them (because they’re less spread-out within the body)
2) They then serve as markers that stimulate phagocytosis to engulf the bacterial cells to which they are attached

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6
Q
A
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7
Q

What’s the importance of the variable regions

A

It’s the variable region that will determine the antigen specificity, giving a specific response

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8
Q

What type of protein is an antibody

A

Antibody is an example of globular proteins

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9
Q

Explain how a change in the primary structure of a globular protein may result in a different 3D structure, and the consequence of this on the immune response (5 marks)

A
  • Primary structure is the sequence of amino acids
  • Determines positioning of bonds and therefore tertiary structure
  • This determines shape of variable region of antibody
  • which is specific/complementary to one type of antigen
  • change in the variable region = the antigen can no longer bind/no antigen-antibody complex formed
  • Pathogen can no longer be formed
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10
Q

When is neutralisation used

A

Some pathogens make us ill by producing toxins
—> some antibodies work by neutralising these toxins

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11
Q

What is a complement cascade

A
  • the binding of an antigen to the surface of a pathogen can set off a chain reaction with blood proteins
  • which causes the pathogen to swell up and burst
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12
Q

What are the 3 ways that antibodies work

A
  • Agglutination
  • Neutralisation
  • Complement cascade
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13
Q

What are monoclonal antibodies

A
  • antibodies produced from a single group of genetically identical (cloned) B-cells
  • therefore, they’re all identical in structure
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14
Q

Are antibodies specific?

A
  • yes
  • their binding sites have a uniques tertiary structure that only one particular antigen will fit into
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15
Q

What are the uses of monoclonal antibodies

A
  • Cancer treatment (both direct and indirect)
  • Medical diagnosis / ELISA
  • Pregnancy testing
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16
Q

How can monoclonal be used for cancer treatment

A
  • monoclonal antibodies can be used to target specific substances, e.g. cancer cells
  • therefore they can be used in many different ways to treat cancer:
    1) direct monoclonal antibody therapy, e.g. Herceptin
    2) indirect monoclonal antibody therapy,
17
Q

Explain direct monoclonal antibody therapy

A
  • monoclonal antibodies are produced that are specific to antigens on cancer cells
  • These antibodies are given to a patient and attach themselves to the receptors on their cancer cells
  • They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth
18
Q

Give an example for a monoclonal antibody used in direct monoclonal antibody therapy

A

Herceptin
- treats breast cancer

19
Q

What is the advantage to direct monoclonal antibody therapy

A
  • antibodies are not toxic
  • antibodies are highly specific
    —> leads to fewer side effects, than other forms of therapy
20
Q

Explain indirect monoclonal antibody therapy

A
  • attaching a radioactive or cytotoxic drug (a drug that kills cells) to the monoclonal antibody
  • when the antibody attaches to the cancer cells = kills them
21
Q

Why are monoclonal antibodies used in indirect monoclonal antibody therapy sometimes referred to as ‘magic bullets’

A
  • used in smaller doses, as they target only specific sites
  • this is not only cheaper, but also reduces any side effects that the drug may have
22
Q

Which diseases can be diagnosed using monoclonal antibodies

A
  • influenza
  • hepatitis
  • chlamydia
    —> produces a much more rapid result than conventional methods for diagnosis
23
Q

How can monoclonal antibodies be used to diagnose prostate cancer

A
  • men with prostate cancer produce more of a protein called prostate specific antigen (PSA), leading to unusually high levels of it in the blood
  • by using the monoclonal antibodies that interacts with this antigen = obtain a measure of the level of PSA in a sample of blood
  • whilst higher than normal levels of PSA in the blood isn’t diagnostic of the disease, it does give early warnings and the need for further tests
24
Q

How are monoclonal antibodies used in pregnancy testing

A
  • placenta produces hormone: human chorionic gonadatrophin (hCG)
  • hCG can be found in the mothers urine
  • monoclonal, antibodies present on the test strip of a home pregnancy testing kit are linked to coloured particles
  • if hCG present in urine it will bind to these antibodies
  • the hCG-antibody-colour complex moves along the strip until its trapped by a different type of antibody
    —> creating a coloured line
  • they will also create a second line at the bottom, regardless of whether hCG is present or not (acts as a control, showing if the test is faulty or not)
25
Q

What are some of the ethical issues with using monoclonal antibodies

A
  • production of MA includes use of mice being deliberately induced to produce both antibodies and tumour cells
  • there are some deaths associated with the use of MA in treating multiple sclerosis. (To get around this, patients need to give INFORMED CONSENT)
  • possible side effects, e.g. the trials for the monoclonal antibody (TGN1412) lead to multiple organ failures

A Level Biology: Cell recognition and the immune system (8 decks)

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