Cooking an egg.
Last week in the woods we cooked an egg using half an orange
peel as a container, but what was happening whilst it cooked?
What is in an egg?
As an egg is the place where an embryo will develop until it is ready to be born it contains almost everything that is required for life (2). Proteins form around 12% of an egg, these are made up of one or more
long chains of amino acids. The order and type of these acids effects the shape
of the protein and therefore what job it will do within the cell. These jobs
range from the replication of DNA to acting as gateways through cell walls
(remember the photosynthesis song).
The bonds between various amino acids causes the chains to
bend into structures known as an Alpha- helix or a beta- sheets (4).
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| Amino acids forming an Alpha- helix (1) |
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| Amino acids forming a Beta-sheet. (1) |
Some parts of these structures are what is known as
‘hydrophobic’ this means they will repel water and will cause the protein to
bend in on itself. This creates the complex 3d shape that allows a protein to fulfil its function (4).
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| A complex protein made from two chains of amino acids. |
Changes during cooking.
When heated the molecules in a protein begin to vibrate more
vigorously this breaks the bonds between amino acids causing the protein to
‘denature’ and loose its shape.
New bonds are then formed between the long chains amino acids creating a solid mass that we can now eat (3). You can see this happen as the clear 'egg white' turns opaque.
Beating an egg.
We do not always cook our eggs before we eat them, a chocolate moose contains 'raw' egg. So what happens when we beat an egg that allows us to eat it?
The answer is very similar to cooking an egg, this time instead of a heat source providing the energy to break bonds, the action of beating itself will denature the proteins stretching them into long chains which trap air creating a moose (5).
Rob Jones
1) Answers.com
2) http://www.nutritionandeggs.co.uk/basic/nutritional-value-eggs3)http://voices.yahoo.com/the-kitchen-chemist-happens-fry-egg-2969005.html
4) http://www.nlm.nih.gov/medlineplus/ency/article/002467.htm
5) http://cooking.stackexchange.com/questions/11305/what-does-beating-eggs-actually-do-chemically-speaking
Yes, the three dimensional structure of any protein is so important in determining its properties - and while we are great at lab chemistry, one thing we can't do is get long chains of amino acids to bend and twist in the precise shape (="conformation") needed for a protein to be "active".
ReplyDeleteThanks for the reminder about the song from the Biochemists Songbook. I learned the other day that one of our Nat Sci 2nd years who does a bit of singing for fun was invited back to the home of one of the other singers - to sing of course - and it turned out to be the composer of Photosynthesis and other great biochemistry songs, now retired but still singing in Selsey!