Amino Acids: Definition, Structure, Types and Importance
Amino acids are one of the most important topics in Class 12 Chemistry and basic biochemistry. Questions related to amino acids are frequently asked in CBSE board examinations, NEET, JEE and even in practical viva. Amino acids are the fundamental building blocks of proteins and play a vital role in the structure and functioning of living organisms.
What are Amino Acids?
Amino acids are organic compounds that contain both an amino group (–NH2) and a carboxyl group (–COOH) in the same molecule. Because they contain both acidic and basic functional groups, amino acids show unique chemical behavior.
General definition:
Amino acids are compounds which contain one amino group and one carboxylic acid
group attached to the same carbon atom.
General Structure of Amino Acids
The general structure of an amino acid is:
H
|
H2N – C – COOH
|
R
Here, R represents the side chain. The nature of the R-group determines the properties and type of the amino acid.
General formula:
H2N – CH(R) – COOH
Zwitterion Nature of Amino Acids
In aqueous solution, amino acids exist as zwitterions. A zwitterion is a molecule that carries both positive and negative charges but is electrically neutral overall.
Zwitterion form:
H3N+ – CH(R) – COO−
Because of this zwitterionic nature:
- Amino acids have high melting points
- They are crystalline solids
- They behave as both acids and bases (amphoteric nature)
Classification of Amino Acids
Amino acids are classified in different ways based on nutrition, structure, side chain properties, and metabolic behavior.
1. Classification Based on Nutritional Requirement
(a) Essential Amino Acids
Essential amino acids are those which cannot be synthesized by the human body and must be obtained through diet.
Examples of essential amino acids:
- Valine
- Leucine
- Isoleucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
These amino acids are very important for growth and tissue repair.
(b) Non-Essential Amino Acids
Non-essential amino acids are those which can be synthesized by the human body.
Examples:
- Glycine
- Alanine
- Serine
- Aspartic acid
- Glutamic acid
2. Classification Based on Side Chain Polarity
(a) Non-Polar Amino Acids
These amino acids have non-polar side chains and are hydrophobic in nature.
- Glycine
- Alanine
- Valine
- Leucine
- Isoleucine
(b) Polar but Uncharged Amino Acids
These amino acids have polar side chains but no net charge.
- Serine
- Threonine
- Asparagine
- Glutamine
- Tyrosine
(c) Charged Amino Acids
Positively charged (basic) amino acids:
- Lysine
- Arginine
- Histidine
Negatively charged (acidic) amino acids:
- Aspartic acid
- Glutamic acid
3. Classification Based on Nature of Side Chain
(a) Aliphatic Amino Acids
- Glycine
- Alanine
- Valine
- Leucine
(b) Aromatic Amino Acids
- Phenylalanine
- Tyrosine
- Tryptophan
(c) Sulphur-Containing Amino Acids
- Cysteine
- Methionine
4. Classification Based on Metabolic Fate
(a) Glucogenic Amino Acids
These amino acids are converted into glucose during metabolism.
- Alanine
- Glycine
- Aspartic acid
(b) Ketogenic Amino Acids
These amino acids are converted into ketone bodies.
- Leucine
- Lysine
(c) Both Glucogenic and Ketogenic
- Isoleucine
- Phenylalanine
- Tyrosine
- Tryptophan
Important Properties of Amino Acids
- Amino acids are colorless, crystalline solids
- They are soluble in water
- They have high melting points
- They show amphoteric behavior
Biological Importance of Amino Acids
Amino acids are extremely important for living organisms.
- They are building blocks of proteins
- They help in enzyme formation
- They are required for growth and tissue repair
- They play a role in hormone synthesis
- They are essential for neurotransmitter formation
Conclusion
Amino acids are the fundamental units of life. Their structure, classification, and properties are very important for understanding proteins and biological processes. A strong understanding of amino acids helps students score high marks in CBSE boards and competitive examinations.
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