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Topic last updated: 30 Sept 2021

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Diabetes 16+

5  of  10

Discovery of insulin

In 1921 two researchers, Fred Banting and Charles Best, were the first to discover insulin and use it to treat diabetes.

Animal testing

At the time that Banting and Best were looking for a cure for diabetes, there were no alternatives but to perform their experiments using animals.

To test their theory Banting and Best used 10 dogs. They made the dogs diabetic and then investigated treatments for the diabetes. The result of their research has saved the lives of millions of people.

Injecting insulin allows
individuals with diabetes to
control their blood sugarblood sugar
 The sugar (glucose) dissolved in the blood; the normal range is 4.0 - 7.8 mmol/l. levels.

Banting and Best's discovery of insulin

 

Some people have very strong opinions about testing medicines on animals. Today the use of animals is very tightly regulated and only allowed in circumstances where there are no other viable alternatives.

Using animals for biomedical research is highly regulated in the UK. The law contains these principles:

  • The required information cannot be obtained using non-animal methods.
  • The likely benefits of doing the tests must outweigh any possible distress to the animals.
  • The test should use the minimum number of animals, appropriate species and cause the minimum distress.
  • Proper veterinary care should be given at all times.
  • Non-animal alternativesNon-animal alternatives
     Processes such as cell culture, computer modelling, imaging and microdosing of human volunteers that can give information on potential harmful effects of a substance, without the need of using animals.      should be used wherever possible.
  • The person doing the test needs to be fully trained. Permission from the Home OfficeHome Office
     The UK government department responsible for regulating the use of animals in scientific research.      must be given before the study can begin.
  • The location for the tests must have all the necessary staff and facilities to ensure that animals are properly looked after.
  • Inspectors regularly monitor the locations where tests are being performed to check that all requirements are being met.

 

Insulin

Banting and Best did not know the chemical structure of insulin. In 1955, Fred Sanger determined its amino acidamino acid
 The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body. sequence, and in 1969, Dorothy Hodgkin used X-ray crystallographyX-ray crystallography
 A technique that uses the diffraction of X-rays to determine the molecular structure of a crystalline substance.  to find its three-dimensional structure.

The insulin molecule acts by attaching to cell-surface receptorsreceptors
 Protein molecules attached to cells that only bind to specific molecules with a particular structure. on its target cells. Its three-dimensional structure enables it to attach to these receptors. The shape of the insulin molecule is determined by the way the protein chains fold around each other due to hydrogen bondhydrogen bond
 An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule. s and disulphide bridges.

Insulin is a protein made up of two amino acid chains.

 

Protein structure

The three dimensional structure of protein is described using four categories:

  • Primary
    Amino acidamino acid
     The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body.     sequence of the polypeptidepolypeptide
     A long chain of hundreds or even thousands of amino acids joined by peptide bonds.     chain. e.g., amino acids in insulin's A and B chains, or haemoglobinhaemoglobin
     The protein that carries oxygen within red blood cells.     's α and β chains.
  • Secondary
    How the amino acid chain folds back onto itself. Typically β-sheets or α-helices.
  • Tertiary
    Folds in the β-sheets or helices to give overall structure of the polypeptide chain. This would be the structure of each individual chain.
  • Quaternary
    Some proteins are made of more than one polypeptide chain. These are joined to make the functioning protein. This is known as a heterodimer, i.e., two different chains. This is the active form of insulin. However, insulin is stored in cells in the form of a hexamer, six units of insulin, arranged in the form of three dimers.

    Therefore, insulin has three quaternary structurequaternary structure
     In some proteins several polypeptide chains fit together to form a larger molecule. The quaternary structure refers to the way the different polypeptide chains fit together.     s: two for the active and a different one for the inactive conformation.
Insulin Monomer Surf
Insulin Homodimer Surf
Insulin Hexamer Surf

Another good example is haemoglobinhaemoglobin
 The protein that carries oxygen within red blood cells. . Its quaternary structurequaternary structure
 In some proteins several polypeptide chains fit together to form a larger molecule. The quaternary structure refers to the way the different polypeptide chains fit together. is a heterotetramerHeterotetramer
 protein complex formed by four subunits, where one, or more subunits, are different. . The active conformation is formed by the arrangement of two copies of the α and two copies of the β chain. Each one binds a haem group.

Hemoglobin Tetramer Surf Hq
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