What are two examples of amino acids?

January 5, 2026 •

3 min read

There are 20 standard amino acids that are the fundamental building blocks of proteins, which are essential for countless bodily functions. Based on how our body acquires them, these compounds can be broadly categorized as essential or non-essential, and what are two examples of amino acids with different classifications are Glycine and Lysine.

Quick Summary

Amino acids form proteins, but their function varies. Glycine is a non-essential amino acid, while Lysine is essential, and their distinct side chains dictate unique roles within the body's structure, metabolism, and neurotransmission.

Key Points

Glycine's Simplicity: The simplest amino acid, with a single hydrogen R-group, makes it highly flexible in protein structures like collagen.
Lysine's Essential Nature: An essential amino acid that must be obtained from dietary sources because the human body cannot synthesize it.
Functional Differences: Glycine acts as an inhibitory neurotransmitter, while lysine is crucial for producing hormones, enzymes, and absorbing calcium.
Structural Roles: Glycine contributes to collagen's flexibility, while lysine helps stabilize the collagen matrix, essential for connective tissues.
Classification is Key: Understanding the difference between essential and non-essential amino acids, as exemplified by lysine and glycine, is vital for proper nutrition and bodily function.

Understanding Amino Acids: The Building Blocks of Life

Amino acids are organic compounds that serve as the monomers for building proteins. Each amino acid shares a fundamental structure: a central carbon atom (the alpha-carbon) bonded to an amino group ($ -NH_2 $), a carboxyl group ($ -COOH $), and a hydrogen atom. The fourth bond of the alpha-carbon is to a unique side chain, or "R-group," which determines the specific characteristics of each amino acid, such as its size, polarity, and charge. It is this R-group that provides the diversity among the 20 common amino acids and dictates how they interact to form complex protein structures.

The Three Main Classes of Amino Acids

Amino acids are classified based on whether the human body can synthesize them. This categorization helps determine their dietary importance.

Essential Amino Acids: These nine amino acids cannot be synthesized by the body and must be obtained through diet. They include Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.
Non-Essential Amino Acids: These amino acids can be produced by the body and do not need to be sourced from food. The 11 non-essential amino acids are Alanine, Arginine, Asparagine, Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline, Serine, and Tyrosine.
Conditionally Essential Amino Acids: This category includes non-essential amino acids that become essential during certain life stages or in times of high stress or illness. For instance, Glycine and Arginine can become conditionally essential under conditions like illness, infancy, or trauma.

Example 1: Glycine (Non-Essential)

Glycine is the simplest amino acid, with a single hydrogen atom as its R-group, granting it flexibility important for protein structures like collagen. It's a key component of collagen, making up about a third of this protein vital for connective tissues. Glycine also functions as an inhibitory neurotransmitter in the central nervous system, regulating motor control and sensory perception, and is used in producing the antioxidant glutathione.

Example 2: Lysine (Essential)

Lysine is an essential amino acid characterized by a long, positively charged side chain. Since the body cannot produce it, dietary intake from sources like meat, fish, and legumes is necessary. Lysine is crucial for calcium absorption and retention, supporting bone and teeth health. It is also essential for forming the triple-helix structure of collagen, aids in producing enzymes and hormones, supports immune function, and is needed for tissue growth and repair.

Comparison of Glycine and Lysine


Feature	Glycine	Lysine
Classification	Non-Essential	Essential
Side Chain	A single hydrogen atom, making it the simplest and most flexible amino acid.	A positively charged amino group ($ -NH_3^+ $), making it a basic amino acid.
Primary Role	Provides structural flexibility in proteins like collagen; acts as an inhibitory neurotransmitter.	Crucial for calcium absorption, hormone production, and the structural integrity of collagen.
Dietary Source	Produced by the body, though also found in protein-rich foods.	Must be obtained from food sources such as meat, fish, eggs, and legumes.
Molecular Charge	Neutral at physiological pH, although it is a zwitterion.	Positively charged at physiological pH due to its basic side chain.

The Broader Impact of Amino Acids

Amino acids are vital for numerous bodily functions beyond building proteins. They are involved in synthesizing neurotransmitters that influence mood, sleep, and appetite, and can serve as an energy source, particularly during prolonged exercise. Amino acids are also essential for muscle growth and maintaining healthy skin, hair, and nails. Consuming a balanced diet with complete protein sources is important to ensure adequate intake of all nine essential amino acids. Deficiency in any essential amino acid can negatively impact protein synthesis and lead to health issues. For more details on amino acid structure and classification, you can consult resources like Khan Academy Khan Academy.

Conclusion

Glycine and Lysine exemplify the diverse roles of amino acids. Glycine, a simple non-essential type, offers flexibility in protein structures and acts as a neurotransmitter, while lysine, a complex essential amino acid, is critical for calcium absorption and immune function. Their distinct properties, determined by their side chains, highlight how each amino acid contributes uniquely to overall health. Ensuring sufficient intake of all essential amino acids is fundamental for supporting various physiological processes.

Frequently Asked Questions

The primary difference is their classification and side chain. Glycine is a non-essential amino acid with a very simple hydrogen side chain, while lysine is an essential amino acid with a long, positively charged side chain.

A deficiency in lysine can lead to various health problems, including retarded growth, anemia, fatigue, and reproductive issues, due to its importance in forming proteins, hormones, and antibodies.

Yes, the human body can produce glycine on its own, classifying it as a non-essential amino acid. It can also be obtained from protein-rich foods.

Lysine is considered essential because the human body cannot produce it in sufficient quantities to meet its needs, so it must be consumed through the diet.

Excellent dietary sources of lysine include meat, fish, eggs, dairy products, soy, legumes, and certain nuts and beans.

In the central nervous system, glycine acts as an inhibitory neurotransmitter, helping to regulate sensory and motor pathways. Interference with its release can lead to over-excitation, causing spastic paralysis.

Yes, there are nine essential amino acids in total. Besides lysine, they include histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, and valine.

Amino acids link together through covalent bonds called peptide bonds in a process called dehydration synthesis, forming a long chain known as a polypeptide. The unique sequence and folding of these chains create the functional protein.