Antibodies

Question 1

What are antibodies?

Answer 1

They are proteins with specific binding sites and produced by B cells

Question 2

Describe two things about the structure of the (antibodies’) binding sites

Answer 2

• Each antibody has two identical binding sites
• Each antibody binding site (which consists of a sequence of amino acids that form a specific 3D shape that) is complementary to a specific antigen

Question 3

Describe the structure of an antibody and draw a diagram

Answer 3

Made up of 4 polypeptide chains:
- 2 heavy chains (longer chains on inside)
- 2 lighter chains (shorter on the outside at top)
- Antigen binding site (2 at top on either side)
There is a variable region (top area) and a constant region (lower area)

Question 4

Describe the antigen-antibody complex

Answer 4

Each antibody has a specific binding site that fits very precisely onto a specific antigen to form an antigen-antibody complex

Question 5

Why is the variable region described as variable?

Answer 5

The binding site is different on different antibodies

Question 6

What does the constant region do?

Answer 6

Binds to receptors on cells such as B cells

Question 7

True or false?

‘Antibodies destroy antigens directly’

Answer 7

False. They don’t destroy antigens directly but prepare the antigen for destruction

Question 8

Describe two ways in which antibodies assist in the destruction of antigens

Answer 8

• Cause agglutination of bacterial cells + forms clumps of bacterial cells making it easier for phagocytes to locate them as they are less spread out within the body
• They then serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 9

What are monoclonal antibodies?

Answer 9

Antibodies produced from a single group of genetically identical B-cells (plasma cells) specific to one type of antigen

Question 10

Why are monoclonal antibodies identical in structure?

Answer 10

• They have the same primary structure as they are coded for by the same genes
• So have the same secondary + tertiary structures as a result

Question 11

How are monoclonal antibodies produced?

Answer 11

1. The specific antigen binds to the antibody/receptor on the B cell
2. A helper T-cell sends out a chemical signal to activate the B-cell which then releases specific antibodies
3. Thus by using the same plasma cells, identical antibodies will be produced

Question 12

How are monoclonal antibodies used to target drugs?

Answer 12

• The monoclonal antibodies all have the same, unique tertiary structure
• Therefore, they will bind to a specific antigen with a complementary shape
• So you can make monoclonal antibodies bind to specific target molecules e.g a cell antigen
• Usually monoclonal antibodies are taken from mice

Question 13

What is the antibody binding to when treating cancer?

Answer 13

Cancer cells have unique antigens called tumour markers that bind to the antibodies

Question 14

How do the antibodies work when treating cancer?

Answer 14

• Anti-cancer drugs can be attached to antibodies
• Therefore drugs will only be released where antibody binding occurs i.e. at cancer cells
• It reduces side effects as drugs will only accumulate at specific cells

Question 15

What is the antibody binding to in a pregnancy test?

Answer 15

• hCG hormone produced by the placenta in a pregnant woman binds to antibodies
• Form antigen-antibody complex

Question 16

How do the antibodies work in a pregnancy test?

Answer 16

• Monoclonal antibodies are immobilised in coloured beads on a test strip
• When hormones bind to antibodies forming an antigen-antibody complex
• The complex moves along the strip until trapped by a different type of antibody
• Complexes accumulate to produce a coloured line
• Blue if hCG is present confirming the pregnancy

Question 17

Give at least 3 ethical issues with the use of monoclonal antibodies

Answer 17

• Production involves mice to produce the monoclonal antibodies but to do this they need to have tumour cells (giving mice cancer)
• Positive results in treating cancer + diabetes but negative results involving deaths in treating multiple sclerosis (when body’s immune system attacks its own tissues)
• Drug trials for safety of new drugs not always certain (in 2006 a drug trial injected people with new monoclonal antibodies + within minutes 6 participants went into multiple organ failure)