Denaturing proteins
Experiment 1
You will need:
- An egg white
- A glass with alcohol
Procedure
- Pour the egg white in the glass
containing alcohol
- Cover the glass and wait for
at least half an hour
- As time goes by look at what
is happening inside the glass
- Cover the glass and look at
it one day after.
What has happened?
The protein chains
in the egg white are folded taking on a round shape. These are
called globular proteins. When you fry or boil an egg,
the heat causes these protein chains to unfold and new bonds
are formed crosslinking those chains with one another. This
structural change gives the observed aspect to the egg once
it is cooked. This process is known as denaturing and
can be produced in many different ways:
- Heating : fry or boil
- whipping the egg white
- By chemicals such as alcohol,
salt, acetone, etc.
You can do a similar experiment
using kitchen salt instead of alcohol.
Experiment 2
You will need
- Two glasses with some milk at
room temperature
- A little vinegar
- Half lemon
Procedure
- Pour the vinegar in one glass
- Squeeze the lemon in the other
glass
- Shake both glasses to mix their
contents
- Wait a few minutes
- Observe what happens in each
glass
What happened?
Similarly to what happened
with the egg, the acid present in the vinegar (acetic acid)
or in the lemon (citric acid) is able to denature the protein
in the milk called casein.
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