Wheat is Australia’s main winter crop. Sown in autumn and harvested in spring or summer, it provides us with flour to make our daily bread. We eat wheat as toast with vegemite, or sandwiches for lunch. But wheat is not for everyone, as eating it can cause trouble for some people, such as those with celiac disease.
Songs and hymns have been sung for bread, yet even today it has its mysteries. Like all living things, it contains a genome – the collection of its genetic material, such as DNA. Scientists have found the DNA sequence for the genomes of humans, lions, tigers and bears. Oh my, but bread wheat is a whole other story.
“With bread wheat, it is a big challenge,” says Ute Baumann at the Australian Centre for Plant Functional Genomics. “Bread wheat has a genome more than five times larger than the human genome. It’s massive. Rice is tiny by comparison.”
Why so big? Today’s bread wheat came from three ancestor species, which combined thousands of years ago and shared their DNA. Each grain of wheat contains three sub-genomes from the three ancestor species.
In July, an international team of scientists announced that they had made a rough draft of the whole genome of bread wheat, and a detailed version of one single chromosome, 3B. A team in Australia is working now to create a detailed version of chromosome 7A. “There are a number of important traits on chromosome 7A,” says Ute. “It has genes involved in salt tolerance, yield and flour quality.”
The rough draft was made using a method called shotgun sequencing, which breaks the genome into small parts and then sequences them. It’s like a big jigsaw, and the trick is putting all the little pieces together. It’s very difficult, because the wheat genome is very repetitive and a lot of the pieces are the same.
A more detailed version, like the one Australian scientists are working on for chromosome 7A, uses a method called BAC by BAC sequencing. BAC stands for bacterial artificial chromosome, and this method cuts the DNA into much larger sections and grows them in bacteria. This method is slower, but makes it possible to piece the whole chromosome together.
With a map of wheat’s genome, it’s much faster for plant breeders to grow varieties of wheat that are more productive, or better suited to Australian conditions. As the world’s population grows bigger and bigger, better bread wheat needs to be on the menu.
You'll need these things, and a spoon for stirring.
Put two tablespoons of flour and one tablespoon of water into a glass and stir.
In a bowl, put two tablespoons of flour and one tablespoon of water. Mix them together, then knead the dough by pressing it flat and folding it over.
This is how to fold the dough over. Keep pressing and folding it for ten minutes.
Wash the dough in a glass of water, until you are left with a creamy-brown, stretchy blob.
You have now extracted gluten.
You will need
Plain flour
Water
Bowl
Two glasses
Measuring spoons
Spoon
Pen and paper
What to do
Fill two glasses with an equal amount of water. Label one as flour and the other as dough.
In the glass labelled flour, put two tablespoons of flour and one tablespoon of water. Stir well. What happens?
Now we are going to make dough. In a bowl, put two tablespoons of flour and one tablespoon of water. Mix together to form a dough.
Using your hands, knead the dough by pressing it flat and folding it over. Keep up this press-fold, press-fold for ten minutes.
Put the kneaded dough in the glass labelled dough. Use your fingers to wash the dough in the water. You’ll see the water become white – this is the starch or carbohydrate in the flour. Keep washing the dough until you are left with just a creamy-brown stretchy blob – it might take five or ten minutes. You have now extracted gluten.
What’s happening?
When we wash the dough in water, we are separating the dough into the parts that dissolve in water and those that don’t. Starch is one of the parts that dissolve in water. Gluten does not, so this method allows us to extract it.
When you stirred just the flour into the glass labelled flour, you would have noticed that there was no glob of gluten at the end. Why? Gluten is actually formed from two proteins, gliadin and glutenin, both found in flour. When flour is mixed with a bit of water and kneaded, these proteins become hydrated and combine to make gluten. Kneading makes the gluten form a network of fine protein strands. This makes it stick together into a gloopy glob.
Applications
Gluten is tough stuff. Play around with your glob of gluten and feel how strong and elastic it is. Gluten gives bread an elastic texture and traps air bubbles, allowing the bread to rise. Too much gluten in a scone, muffin or pancake will make them tough.
In gluten-free cooking, people might use rice and maize flour instead of wheat, as they don’t contain gluten. To get the dough to rise they need to add extra ingredients, such as guar gum, to do the work that gluten would.
Washing dough to extract gluten is sometimes used in vegetarian cooking. The gluten is collected and used as a meat-free form of protein also known as seitan. It can be dried and powdered, and then used to make an imitation meat.
Artist Sam Van Aken has created a tree that produces 40 different types of stone fruit (PDF). He used a process called grafting, which is commonly used in apple orchards to put a great apple-producing variety onto a variety with good roots.
Watch it! Extract DNA from a banana at home, with this activity from CSIRO.
Quiz answers
A barbel is a type of fish.
LOX is liquid oxygen.
a) The Earth’s crust is approximately 40 kilometres thick.
False. Red blood cells are actually smaller than liver cells.
Drag is created by parachutes to slow objects down.
Our partner
Lloyd’s Register Foundation (LRF) is a proud partner of Science by Email. LRF helps to protect life and property by supporting engineering-related education, public engagement and the application of research.
No hay comentarios.:
Publicar un comentario