classify amino acids?5marks
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Answer:
There are some 20 amino acids in the proteins that we consume. These amino acids bond together to form a larger protein molecule. Amino acid being organic compound molecules can form various different links with each other due to the versatile nature of carbon. This enables the great diversity of proteins that can be found in nature. These are an essential nutrient in our diet because of the functions they perform.
There are actually thousands of amino acids occurring in nature. But only about 20 amino acids form a part of the proteins in the human body. These twenty acids will be our focus here. Although all these have varied structures, the basic structure of amino acid remains uniform.
All amino acids contain a carbon atom in the middle of the molecule, the alpha-carbon
This atom is surrounded by three chemical groups.
One is an amine group -NH2
The second one is a carboxyl group -OOOH
The third group is denoted by R. This is the variable radical group and is different for every amino acid. This R group makes the amino acid unique.
Classification of Amino Acids
Amino Acid can be classified based on their structure and the structure of their side chains i.e. the R chains. Now two basic subcategories are
1] Non-Polar Amino Acids
These are also known as Hydrophobic. The R group can be either of Alkyl groups (with an alkyl chain) or Aromatic groups. The acids falling in this group are stated below. Numbers one to seven are Alkyl and the last two are aromatic
Glycine (H)
Alanine (CH3)
Valine ( CH (CH3)2 )
Methionine ( CH2CH2SCH3 )
Leucine ( CH2CH(CH3)2 )
Isoleucine ( -CH(CH3)CH2CH3 )
Proline (special structure)
Phenylalanine
Tryptophan
2] Polar Amino Acids
If the side chains of amino acid contain different polar groups like amines, alcohols or acids they are polar in nature. These are also known as Hydrophilic Acids. These are further divided into three further categories.
a) Acidic: If the side chain contains an extra element of carboxylic acid component these are acid-polar amino acids. They tend to donate their hydrogen atom. These are:
Aspartic Acid ( CH2COOH)
Glutamic Acid ( CH2CH2COOH )
b) Basic: These have an extra nitrogen group that tend to attract a hydrogen atom. The three basic polar amino acids are
Histidine
Lysine ( CH2(CH2)2NH2 )
Arginine
c) Neutral: These are neither acidic nor basic. They have an equal number of amino and carboxyl groups. Also, they have at least one hydrogen component connected to electronegative atoms. Some of these neutral acids are
Serine ( CH2OH )
Threonine ( CH(OH)CH3 )
Asparagine ( CH2OHNH2 )
Glutamine ( CH2CH2CONH2 )
Cysteine ( CH2SH )
Tyrosine
Amino acid can also be classified on the basis of their need to the human body and their availability in the human body
1] Essential Amino Acids
These are the acids that cannot be synthesized in our bodies. We must rely on food sources to obtain these amino acids. They are
Leucine
Isoleucine
Lysine
Theorine
Methionine
Phenylalanine
Valine
Tryptophan
Histidine (conditionally essential)
2] Non-Essential
These acids are synthesized in our bodies itself and we need not rely on outside sources for them. They are either produced in our bodies or obtained from protein breakdowns
An additional amino acids' classification depends upon the side chain structure, and experts recognize these five as:
• Cysteine and Methionine (amino acids containing sulfur)
• Asparagine, Serine, Threonine, and Glutamine (neutral amino acids)
• Glutamic acid and Aspartic acid (acidic); and Arginine and Lysine (basic)
• Leucine, Isoleucine, Glycine, Valine, and Alanine (aliphatic amino acids)
• Phenylalanine, Tryptophan, Tyrosine and Histidine (aromatic amino acids)
One final amino acid classification is categorized by the side chain structure that divides the list of 20 amino acids into four groups - two of which are the main groups and two that are subgroups. They are:
1. Non-polar
2. Polar
3. Acidic and polar
4. Basic and polar