Chemguide: Support for CIE A level Chemistry


Learning outcome 21.3(c)

This statement is about the importance of hydrogen bonding to the way DNA strands bind together.

Before you go on, you should find and read the statement in your copy of the syllabus.


This is new for the 2016 syllabus, and so there won't be any evidence about exactly what sort of questions CIE will ask until 2016 at the earliest.

You should start by reading the first two pages in a set of pages about DNA. Just read the pages headed "DNA structure" and "DNA replication.

Read the whole of these two pages so that you understand the structure of DNA and how it replicates.

But for learning, concentrate on the hydrogen bonding between the base pairs which hold the two strands of DNA together. You should notice the way that adenine and thiamine are an exact fit as far as hydrogen bonding is concerned, as are guanine and cytosine.

It isn't clear whether CIE expect you to learn the structures of these, but I suspect they probably won't. What you must be able to do is to draw the correct pattern of hydrogen bonding if you are given their structures.

You should also understand how this pairing of A and T, and C and G, allows exact copies of the DNA to be made during replication.


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© Jim Clark 2011 (last modified July 2014)