Tertiary and Quaternary Protein Structure: Revision for UK Exams

Absolutely! Preparing for exams can be daunting, but with the right resources, you'll smash it. Here's a concise study guide and a practice quiz focused on tertiary and quaternary protein structures, tailored for your UK Biology exams. Let's get those concepts crystal clear!

Quick Study Guide

• Tertiary Structure: This refers to the specific, 3D folding of a single polypeptide chain. It's how the polypeptide coils and folds into its unique functional shape.
• Stabilising Interactions for Tertiary Structure: These occur between the R-groups (side chains) of amino acids within the same polypeptide:
  • Hydrogen bonds: Between polar R-groups.
  • Ionic bonds: Between oppositely charged R-groups (e.g., an acidic R-group and a basic R-group).
  • Hydrophobic interactions: Non-polar R-groups tend to cluster together in the interior of the protein, away from water.
  • Disulfide bridges: Strong covalent bonds formed between the sulfhydryl groups ($-SH$) of two cysteine residues. These are crucial for the stability of many proteins.
• Quaternary Structure: This is the structure formed when two or more polypeptide chains (subunits) associate to form a functional protein complex. Not all proteins have quaternary structure (e.g., myoglobin is functional as a tertiary structure).
• Stabilising Interactions for Quaternary Structure: Similar to tertiary structure, these interactions occur between the R-groups, but this time they are between different polypeptide subunits. They include hydrogen bonds, ionic bonds, and hydrophobic interactions. Disulfide bridges can also form between different subunits.
• Significance: Both tertiary and quaternary structures are vital for a protein's specific function, creating active sites for enzymes or binding sites for other molecules. Denaturation (loss of this 3D shape) leads to loss of function.

Practice Quiz

1. Which of the following best describes the tertiary structure of a protein?

1. The linear sequence of amino acids in a polypeptide chain.
2. The formation of alpha-helices and beta-pleated sheets.
3. The specific 3D folding of a single polypeptide chain, stabilised by R-group interactions.
4. The association of multiple polypeptide chains to form a functional protein.

2. Which type of bond is a strong covalent link specifically formed between two cysteine residues and is critical for stabilising the tertiary structure of many proteins?

1. Hydrogen bond
2. Ionic bond
3. Disulfide bridge
4. Peptide bond

3. In an aqueous environment, which interactions primarily drive non-polar amino acid R-groups to cluster in the interior of a protein during its 3D folding?

1. Ionic bonds
2. Hydrogen bonds
3. Hydrophobic interactions
4. Disulfide bridges

4. A protein that consists of four separate polypeptide chains joined together to form a functional complex exhibits which level of protein structure?

1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

5. Which of the following is an example of a protein that famously possesses a quaternary structure?

1. Insulin (two chains)
2. Myoglobin (one chain)
3. Haemoglobin (four chains)
4. Amylase (one chain)

6. All of the following types of bonds and interactions help to stabilise tertiary and quaternary protein structures EXCEPT:

1. Hydrophobic interactions
2. Peptide bonds
3. Ionic bonds
4. Hydrogen bonds

7. What is the primary consequence of a protein losing its specific tertiary and/or quaternary structure due to extreme conditions (e.g., high temperature, pH changes)?

1. Its primary structure is altered.
2. Its amino acid sequence changes.
3. It undergoes denaturation and loses its biological function.
4. It forms stronger disulfide bridges to compensate for the loss of other bonds.