This teaching resource will guide you through consecutive steps to explore the biological structure of the insulin molecule – from primary to quaternary structure.
How to start:
Insulin is initially synthesized as preproinsulin, a 110 amino acid polypeptide that contains additional sequences:
After preproinsulin is translated in the endoplasmic reticulum, an enzyme cuts off the 24 amino-terminal amino acids, leaving proinsulin, which in turn folds and allows the formation of the disulphide bonds between cysteine residues.
At this stage, the protein passes into the Golgi apparatus, where the C peptide is removed, forming mature insulin, which is then stored in the Golgi vesicles.
The mature insulin protein consists of two polypeptide chains (A- and B-chains). The A-chain is composed of 21 amino acids, the B-chain of 30 amino acids.
The mature insulin protein consists of two polypeptide chains (A- and B-chains). The A-chain is composed of 21 amino acids, the B-chain of 30 amino acids (find sequences below).
Compare the A-chains (and the B-chains) of human and pig insulins in the following activity by aligning their amino acid sequences. Are there any differences in the amino acid sequences?
Note: In order to submit the second set of sequences you may need to refresh your page and the MUSCLE search box will be empty again.
Step 1 – Compare the A-chains:
“>>sp|P01308|90-110, Insulin A-chain, Human
>sp|P01315|88-108, Insulin A-chain, Pig
Step2 – Compare the B-chains:
>sp|P01308|25-54, Insulin B-chain, Human
>sp|P01315|25-54, Insulin B-chain, Pig
The secondary structure is determined by two a-helices in the A-chain.
The B-chain has a major a-helix section and a beta-sheet region. It folds sharply around the A-chain (see tertiary structure).
The tertiary structure is stabilized by disulphide bridges (see insulin worksheet). The external part of the protein is polar, while internally it is mostly hydrophobic.
Insulin is formed by two polypeptide chains (A- and B-chains), held together by two disulphide bridges; a third disulphide bridge is situated within the A-chain.
As far as the quaternary structure is concerned insulin tends to form dimers in solution, owing to the formation of hydrogen bonds between the C-terminal ends of the B-chain.
Download and print worksheet:
Take the revision quiz and test your knowledge on this amazing molecule.
Christiane Schaffitzel and her team study the function and three-dimensional structure of ribosomes using a combination of molecular biology, biochemistry and cryo-electron microscopy. In her talk, Christiane gives an overview of the steps involved in protein synthesis and the role ribosomes play in the process. She then illustrates how her research group uses cryo-electron microscopy to study the structures of these fascinating molecules. Christiane’s central research questions are: what we can learn from the make up of these fascinating molecules and how are synthesised proteins targeted to their destinations?
Topic area: Structural & Computational biology, Cell biology
Age group: 16-19
Author: ELLS Team