chemical education

Curious Kids: how do scientists read a person’s DNA

Africa Studio/Shutterstock
Mark Lorch, University of Hull

How do scientists read a person’s DNA? – James, aged 11, Thame, UK

DNA (which stands for deoxyribonucleic acid) contains all the information needed to make your body work. It is also surprisingly simple.

DNA is made from four chemical building blocks, which are arranged one after each other. This sequence is the instruction manual for your body. The building blocks are called adenine, thymine, guanine and cytosine, but we usually just call them A, T, G and C.

Curious Kids is a series by The Conversation that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to and make sure you include the asker’s first name, age and town or city. We won’t be able to answer every question, but we’ll do our very best.

The information in your DNA is bunched into sections called genes. The genes are like sentences in an instruction manual.

Most genes control the everyday running of your body – how it grows hair, digests food or carries oxygen around. So 99.9% of your DNA is exactly the same as everyone else on the planet. The rest is what makes you unique. For example, if you have blue eyes, then a few of the letters in some genes will be different from someone with brown eyes.



As we grow, cells in our body divide. One cell becomes two. Every time this happens each of the new cells needs a full copy of DNA. DNA makes this easy, because it’s made of two strands. When a cell divides the strands split up, and a new copy is made of each one. Let’s look at how this is done.

The letter A on one strand is always opposite the letter T on the other, and G is always opposite C. So a short double strand of DNA might looks like this:

Illustration of matching pairs aligned vertically.
Illustration of a double strand of DNA.
Mark Lorch, Author provided

Let’s see what happens with one of the strands in a dividing cell. First a T is added opposite the first A to make:

DNA illustration
T pairs with A.
Mark Lorch, Author provided

Then an A gets attached to the T like this:

DNA illustration
A pairs with T.
Mark Lorch, Author provided

Next, C get placed opposite G:

DNA illustration
C pairs with G.
Mark Lorch, Author provided

And so on until a whole new double-stranded piece of DNA is made.

Reading DNA

We can use this knowledge of how DNA copies itself to read a person’s DNA.

To do this, a scientist puts the DNA into four tubes. Then they add all the machinery that the cell uses to copy DNA, and lots of extra As, Ts, Cs and Gs into each of the tubes.

Next, they add some DNA letters that have been changed so they can’t join with the next letter in the sequence. You can think of them like pieces of Lego, but with flat tops so you can’t add a brick on top of it. Let’s call these special DNA letters A*, T*, G* and C*.

Each of our four tubes gets some of the special DNA letters added to it: A*s in the first tube, T*s in the second, G*s in the third and C*s in the fourth.

Let’s imagine what happens with our DNA sequence in the tube containing A*.

First, just like before, T is added opposite the first A to make:

DNA illustration
T pairs to A.
Mark Lorch, Author provided

Next, though, an A* might get added to make this:

DNA illustration
An A* is added.
Mark Lorch, Author provided

If this happens, then the next letter can’t get attached to the A*. This is as long as this stretch of DNA gets.

But there’s plenty more DNA and letters in the tube and in some cases a normal A will have been added at that point, followed by two Cs to make this:

DNA illustration
Two Cs are added.
Mark Lorch, Author provided

Next there is a choice again. If an A* gets added the DNA sequence will look like this:

DNA illustration
Then an A*.
Mark Lorch, Author provided

Every time we reach the point where we need to add an A there is a chance an A* might get added, which stops the DNA getting any longer. So in the end these DNA strands get made:

DNA illustration
Different lengths of DNA.
Mark Lorch, Author provided

The scientist reading the DNA knows that each strand in this tube ends in an A*. She then counts how many pairs are in each strand of DNA. By doing this, she can work out that the 2nd, 5th and 7th letters are all As.

She then does exactly the same thing with the other tubes and works out that the 1st and 6th letters are Ts, the 3rd, 4th and 9th letters are Cs and the 7th is a G. By putting that all together, she can read the whole DNA sequence.

Reading DNA is useful because sometimes the letters in the genes aren’t quite right, like a misspelled word in a set of instructions. This might cause some of your cells to not work properly.

For example, just one wrong letter in one particular gene might mean someone is more likely to become diabetic, or get cancer when they are older. Reading someone’s DNA allows doctors to spot and treat these diseases before they become too bad.The Conversation

Mark Lorch, Professor of Science Communication and Chemistry, University of Hull

This article is republished from The Conversation under a Creative Commons license. Read the original article.

By February 22, 2022 11 comments chemical education

The Periodic Dinner table

Chemistry built the modern world, from the materials that make up the everyday objects around us, the batteries in our devices and cleaning products that help to maintain sanitation. All this and much more besides are examples of chemistry in everyday life.

To illustrate this and have a bit of fun along the way we (Phil Bell-Young, the Salter’s Institute for Chemistry and I) put together a demonstration packed show called ‘The Periodic Dinner Table’.
It is a cross between demo lecture, comedy sketch and a game of bingo played on a periodic table. Just watch the video, and when you spot us interacting with an element cross it off on your periodic table (here’s one specially adapted for the show).

And in case you want the answers, you can find them on this video or in these teachers’ notes.

Hope you enjoy the show!

By August 9, 2021 2 comments chemical education, entertainment, fun

Chemistry comes to Minecraft

There has been a spot of role reversal in my house of late. I’ve been at the Minecraft again and my kids are complaining.

A while back Microsoft asked me and Joel Mills to work on the latest update of their amazingly popular game. And that update now includes a whole load of chemistry features!!

The Minecraft chemistry update makes it possible to mix subatomic particles together and create elements from hydrogen to oganesson as well as the isotopes in between. Or you can do a spot of elemental analysis on your Minecraft blocks (with a reasonable approximation to what you might find in reality). And then it is possible to combine elements and manufacture new compounds. These  add some nice new features to the game. I particularly like the way you can add metal salts to the torch and they burn with the appropriate colours. The elephant’s toothpaste, glow sticks  and helium balloons are also really nice additions.

The Element Constructor

The Compound Creator

The chemistry update is part of Minecraft Education Edition (MC:EE), a version of the game designed for use in the classroom (but that doesn’t mean you can’t get a licence yourself, costing the princely sum of $5 per year).  MC:EE is packed with useful features for teachers that many of them would probably like in the real world (with a click of the mouse students are instantly frozen, muted or teleported back to exactly where the teacher wants them).

My contribution to the project has been to advice on the in-game chemistry, a set of lesson plans and a bespoke Minecraft chemistry teaching lab (for which Minecraft Global Mentor Joel Mills should get the credit).

The Minecraft Teaching Lab


Our lessons cover everything from lab safety (in which the students encounter a dangerous lab environment and have to spot the hazards and then reduce the risk of accidents by sorting it out) to a spot of analytical chemistry  (using the game’s new material reducer).

Microsoft have done a cracking job of integrating chemistry in their virtual play world. But they are very much aware that the game isn’t (and can never be) and accurate chemistry simulator. Instead it is really designed to stimulate an interest in the subject. Which is why we also included lessons that encourage students to compare how the rules that govern the Minecraft world differ from that of the real world.





By February 22, 2018 3 comments chemical education, Uncategorized

Halloween Chemistry: Cinder Toffee!

How about a spot of halloween chemistry? With nice simple explanations for the trick or treaters.

Cinder toffee!!

You’ll need:

  • Sugar
  • Golden syrup
  • A jam/jelly thermometer
  • Bicarbonate of soda
  • Grease proof paper
  • A baking tray
  • A saucepan


The toffee mix gets very hot, be careful when handling in and make sure there’s an adult helping.

What to do:

1. Weigh out 100grams (3.5 oz) of sugar into the saucepan.
2. Add 3 tablespoons of syrup
3. Heat the mixture on a stove whilst stirring it.
4. Check the temperature of the mixture.
5. Carry on heating until it reaches 145-150oC (293-302).
6. Quickly stir in 1 teaspoon of bicarb. It will suddenly bubble up.
7. Now pour it into the baking tray, lined with grease proof paper.
8. Leave it to cool.

9. Break it all up (best done with a hammer) and enjoy!

What’s going on?
So that’s a nice simple recipe for a tasty treat but where is the science?

First off there’s the sugar and syrup. There are actually loads of different types of sugars, the stuff you put in your coffee and the granulated sugar used here is sucrose. It looks like this:

Golden syrup is a mixture of water, sucrose and two other sugars called fructose and glucose. They look like this:
Sucrose is actually made up of a fructose and glucose molecule that have been joined together.
So why do we need these three sugars to make the toffee? Well, when they are mixed all together they interfere with crystal formation. To explain how this works let’s represent each of the sugars with a different shape.
If we have one type of sugar then the molecules can pack together nice and neatly, like in the diagram. And that is exactly what happens in a crystal. But if you mix them all together they can’t form ordered patterns and so you don’t get crystals forming.
So if we tried to make the toffee with just one type of sugar then we’d end up with crystals forming which make for hard dense toffee (more like a boiled sweet). But by using 3 different sugars the crystals don’t form and instead you end up with a brittle, crunchy, glass like toffee.
Then there’s the bicarbonate of soda. You normally put this in cakes to make them rise. That’s because when you heat up the bicarb it turns to carbon dioxide gas (hence the bubbles in your cakes). The same thing happens here. When you spoon the bicarb into the hot sugar it almost instantly gets converted to carbon dioxide and causes the mixture to foam up.

Hope you enjoy the toffee and whilst you do you can find out more about the science of cinder toffer here.

By October 31, 2015 6 comments chemical education, entertainment, fun