All material designated for higher level only is presented in italics
|Syllabus content to be covered: | | | |Composition | |Basic structure of amino acids | |Essential amino acids, peptides, peptide bond, hydrolysis |
Basic Structure of Amino Acids
The protein molecule has a large complex structure. Each molecule is made up of smaller units called amino acids. Amino acids are the building blocks of the protein molecule. Amino acids are relatively small molecules. They are water-soluble and consequently can easily diffuse through the walls of the intestine.
There are 20 common amino acids. These are arranged like beads in a necklace in many different sequences to form proteins. The number of amino acids and the sequence in which they are arranged results in the formation of particular proteins. It is not altogether unlike how words are formed from the alphabet. There are a huge number of words that can be formed from the 26 letters of the alphabet. Depending on how you sequence the letters and how many letters you use you get different words. Likewise there are many different proteins that can be formed from the 20 common amino acids. In fact even simple proteins contain quite a number of amino acids e.g. insulin (protein) is made up of approx 50 amino acids. Haemoglobin has 500 and urease (protein in soya beans) has over 4500 amino acids.
All amino acids have the same basic structure. They all have a carbon atom (C) at the centre, and radiating from this - an amino group- NH2 (alkaline), a carboxyl group - COOH (acid) and a hydrogen atom common to all amino acids. In addition all amino acids have another atom/group. This varies depending on the amino acid.
If you look at a diagram of a typical amino acid e.g. glycine you will notice as with all amino acids that it has a central carbon atom and attached to this is an amino group (NH2), a carboxyl group (COOH), a hydrogen atom and a variable. In the case of the amino acid glycine, the variable is a hydrogen atom.
Show diagram of amino acid glycine
In the case of the amino acid cysteine again there is a central carbon atom and attached to this is an amino group (NH2), a carboxyl group (COOH), a hydrogen atom and a variable. In the case of the amino acid cysteine the variable is HS- CH2.
Show diagram of amino acid cysteine
Essential Amino Acids
The body can make many of the amino acids it needs e.g. glycine, cysteine and alanine. However there are eight amino acids which the body cannot manufacture successfully. The body needs these hence they are known as the essential amino acids. They are obtained by eating foods that have these amino acids. The eight essential amino acids are:
|Essential Amino Acids |
|Valine |Methionine |
|Lysine |Phenylalanine |
|Leucine |Tryptophan |
|Isoleucine |Threonine |
|Also Essential for Children |
|Arginine |Histidine |
A further two amino acids are essential in the diet of children (because they cannot make them fast enough for their growing needs). They are: Arginine & Histidine
How Are Proteins Formed?
Proteins are formed when different amino acids are joined/linked together. The amino acids link together to form three-dimensional chains called polypeptide chains.
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