Tertiary Level of Protein Structure

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As a follow up to the last blog post, I would like to talk in detail about my favourite level of structure found in a protein: the tertiary structure.

The tertiary structure is further folding of the polypeptide chain. Here, the main bonds are formed from the interactions among the R-groups of the different amino acid residues. These bonds are as follows:

  1. Hydrophobic Forces  the polypeptide chain folds in such a way that their non-polar side chains are out of contact with water. This is called the Hydrophobic Effect.
  2. Hydrogen Bonding- this is formed between H and an electronegative atom (such as O). These 2 different amino acid residues are far apart, but interact because of the folding.
  3. Electrostatic Forces– this results in the formation of ionic bonds.
  4. Disulphide Bonds this is formed from the oxidation of, for example, 2 cysteine molecules, resulting in a strong covalent disulphide linkage between the 2 sulphur atoms.

All of these bonds are represented in the following diagram:

protein_bonds2

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Test For Polysaccharides- Iodine Test

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As you all probably don’t know, my favorite colours are blue & black. And that is the reason why I like this test, because the positive results of it (if a polysaccharide is present) is a blue-black precipitate colour.
The actual test simply consist of adding a few drops of iodine solution to an unknown solution and observing the colour change. Polysaccharides, such as starch and glycogen, would form a blue-black complex with the iodine, resulting in the blue-black colour of the precipitate. The following picture shows what the possible positive results are:

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