Up Learn – A Level biology (AQA) – Biological Molecules
Tertiary Structure of Protein – Part 2
A protein’s tertiary structure is caused by hydrogen bonds, ionic bonds, and disulfide bridges forming between the side groups of amino acids in the polypeptide chain.
We’ve now seen that there are three different bonds that can be formed between the side groups of amino acids.
So, how exactly do these bonds cause polypeptide chains to fold up into tertiary structures, like this?
Well, to start, take this polypeptide chain
Now, if we zoom in on one section of it
… we can see that there are lots of side groups popping out of the chain of amino acids.
And these side groups interact, and form bonds.
For instance, this side group and this side group form…
These two side groups form an ionic bond.
And, this side group and this side group form…
These two side groups form a hydrogen bond.
And this side group and this side group form…
These two side groups form a disulfide bridge.
Now, as a result, all of these parts of the polypeptide chain are pulled even closer together…
… causing it to fold into a tertiary structure, like this
And this tertiary structure gives the polypeptide chain a new shape that isn’t just a helix or a pleated sheet
It twists and turns in all directions… a tangle of alpha helices with beta pleated sheets.
Giving a shape that is more three-dimensional.
So, the tertiary structure is the 3D folding of the polypeptide chain…
…caused by hydrogen bonds, ionic bonds and disulfide bridges between the side groups of amino acids.
So, now, which of these shows part of the tertiary structure of a protein?
These two shapes are formed from a combination of hydrogen bonds, disulfide bridges and ionic bonds. So these are part of a protein’s tertiary structure.
To sum up…
In the different levels of protein structure, the tertiary structure is…
The tertiary structure is the three-dimensional folding of the whole polypeptide chain.
And, the types of bonding that cause the tertiary structure are…
The types of bonding that cause the tertiary structure are hydrogen bonds, ionic bonds and disulfide bridges between the side groups of amino acids.