Protein structure

Describe the secondary structure of proteins

• Hydrogen bonds form between amino

  acids in the polypeptide chain causing it to

  form either α-helix or β-pleated sheets.

• Weak bonds, causes long polypeptide chain to be twisted into a 3D shape

Describe the tertiary structure of proteins

E.g Myoglobin → Protein found in muscles

• Proteins are only functioning when they form their tertiary structure

• Protein folds & forms shape needed using a variety of bonds to keep specific 3D shape

What is the first bond in the tertiary structure of proteins?

• Weak Hydrogen bond

• Forms between slightly positively-charged

hydrogen atoms in some R groups and slightly negatively charged atoms in other R groups.

What is the second bond in the tertiary structure of proteins?

• Hydrophobic attraction between R group → Repels water

What is the third bond in the tertiary structure of proteins?

Ionic bonds: attractions between negatively-charged R groups and positively-

charged R groups.

What is the fourth bond in the tertiary structure of proteins?

• Disulfide bond/bridge, very strong covalent bond between two R-groups & not easily broken

Describe the quaternary structure of proteins

• Proteins are made up of two or more polypeptide chains that interact

• E.g haemoglobin, antibodies

Describe the test for proteins

• Biuret test detects peptide bonds

1. Place a sample of tested solution into a test tube & add an equal volume of sodium hydroxide solution at room temp

2. Add a few drops of very dilute (0.05%) copper (II) sulphate solution & mix gently

3. A purple coloration indicates the presence of peptide bonds & hence a protein. If no proteins, the solution remains blue.