Protein Interactions (AQA A Level Biology): Revision Note

Exam code: 7402

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Cara Head

Updated on

Proteins: interactions & bonds

  • A polypeptide chain will fold differently, into its tertiary structure, due to the interactions (and hence the bonds that form) between R groups

  • Each of the twenty amino acids that make up proteins has a unique R group, and therefore, many different interactions can occur, creating a vast range of protein configurations and therefore functions

  • Within tertiary structured proteins are the following bonds:

    • Strong covalent disulfide

    • Weak hydrophobic interactions

    • Weak hydrogen

    • Ionic

Disulfide

  • Disulfide bonds (also known as disulfide bridges) are strong covalent bonds that form between two cysteine R groups (this is the only amino acid with an available sulfur atom in its R group)

  • These bonds are the strongest within a protein, but occur less frequently, and help stabilise the proteins

  • They can be broken by reduction

  • Disulfide bonds are common in proteins that are secreted from cells e.g. insulin

Ionic

  • Ionic bonds form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups

  • Ionic bonds are stronger than hydrogen bonds, but they are not common

  • These bonds are broken by pH changes

Hydrogen

  • Hydrogen bonds form between strongly polar R groups

  • These are the weakest bonds that form, but the most common, as they form between a wide variety of R groups

Examiner Tips and Tricks

You need to be able to determine which bonds are found in tertiary structures and recognise them in diagrams.

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Subject Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Cara Head

Reviewer: Cara Head

Expertise: Biology & Psychology Content Creator

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding