# Amino Acids: Definition, Structure, Classification (2023)

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Amino Acids are chemical molecules that combine to produce proteins and are hence known as the building blocks of proteins. These biomolecules have a role in a variety of biological and chemical activities in the human body and are essential for human growth and development. There are around 300 amino acids found in nature.

Basic amino groups (-NH2) and carboxyl groups (-COOH)are found in amino acids. Amino acids are the main components of proteins. Proteins and peptides are both made up of lengthy chains of amino acids. There are twenty amino acids in all that are used in the production of proteins. On this page, let us learn everything about Amino Acids in detaul. Read further to find more.

(Video) 1: Amino Acids : General structure, Classification, Significance | Amino acid Chemistry-1| Biochem

## What is Amino Acids?

Proteins are the molecular mass complex biomolecules of amino acids present in all living cells. In other words, amino acids are the building blocks of proteins. There are about $$500$$ naturally occurring amino acids known to us.

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### Structure of Amino Acids

$$\alpha$$- amino acids are building blocks of proteins. Amino acids are organic compounds containing both amino groups and carboxylic groups.

General Formula: General formula:

The amino group $$\left( {{\rm{ – N}}{{\rm{H}}_{\rm{2}}}} \right)$$ may be attached to any carbon atom other than that of the carboxyl $$\left( {{\rm{ – COOH}}} \right)$$ group.

### What are the Properties of Amino Acids?

1. They are colourless, crystalline substances.
2. They have a high melting point.
3. The solubility in water varies with the nature of the side chain.
4. They are amphoteric in nature, i.e., they react with both acids and bases.
5. They have asymmetric carbon except for glycine, hence rotate plane polarised light. This property is called optical activity.

### Classification of Amino Acids

#### Classification Based on the Requirement of the Body:

(a) Non-essential amino acids: These amino acids are synthesized in the body and do not require them in our diet. There are ten non-essential amino acids out of $$20$$. They are glycine, alanine, serine, cysteine, glutamine, tyrosine, proline, aspartic acid, asparagine, glutamic acid.

(b) Essential Amino Acids: These amino acids are not synthesised in the body, and we require them in our diet. There are ten non-essential amino acids out of $$20$$. They are valine, leucine, isoleucine, arginine, lysine, threonine, phenylalanine, tryptophan, and histidine. These essential amino acids are required for our body’s growth, and lack of these in diet can cause diseases such as kwashiorkor.

(Video) Classification of amino acids | Chemical processes | MCAT | Khan Academy

#### Classification of Naturally Occurring Amino Acids

The naturally occurring amino acids can be classified into three groups: Aliphatic, Aromatic, and Heterocyclic amino acids.

Aliphatic Amino Acids: They are long-chain amino acids. They are further classified into the following types of amino acids:

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1. Neutral Amino Acid: It contains an equal number of carboxylic and amino groups in their molecules.
Example: Glycine, alanine, valine, etc.

2. Acidic Amino Acid: Contains a greater number of the carboxylic group than amino groups in their molecules.
Examples: Aspartic acid, glutamic acid which contains two $${{\rm{ – COOH}}}$$ groups and one $${\rm{ – N}}{{\rm{H}}_{\rm{2}}}$$ group.

3. Basic Amino Acid: It contains a greater number of amino groups than carboxylic groups in their molecules.
Example: Lysine, arginine, and histidine, which contains two $${\rm{ – N}}{{\rm{H}}_{\rm{2}}}$$ groups and $${{\rm{ – COOH}}}$$ groups.

4. Sulphur Containing Amino Acid: It contains sulphahydryl $$\left( {{\rm{ – SH}}} \right)$$ groups in their structure.
Example: Cysteine and Methionine

(Video) Amino Acid | Intro | Definition | Structure | Classification in detail | Biochemistry | BP203T | L~7

Aromatic Amino Acid: They contain a benzene ring in their structure.
Example: Phenylalanine and Tyrosine

Heterocyclic Amino Acids: They have a heterocyclic ring with at least one atom other than carbon in their side chain.
Example: Tryptophan, Proline, and Hydroxyproline

### How is Protein Formed from Amino Acids?

When amino acids unite to form proteins, the amino group of one amino acid molecule forms a chemical bond with the carboxylic group of the other. The resulting linkage is called a peptide bond. This linkage process continues until all amino acids necessary for the formation of a protein are joined together. This process involves the loss of one water molecule between the two amino acids.

The joining of two amino acids in this manner forms a larger unit called a peptide. Several peptides joined together to form a polypeptide. In turn, polypeptides unite to form a complete protein.

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### What is the Role of Amino Acid in Our Body?

1. Some amino acids are converted into biologically active compounds. Example: Tyrosine is converted into hormone thyroxine and adrenaline and also into a skin pigment, melanin.
2. Glycine is involved in the formation of heme (haemoglobin protein) and tryptophan from the vitamin nicotinamide and the plant hormone indole acetic acid.
3. Amino acids like citrulline and ornithine are actively involved in the urea cycle in the liver and thus helps in maintaining the ammonia concentration below toxics level.

### Summary

The proteins we eat include around 20 amino acids. These amino acids produce a bigger protein molecule when they bind together. Because of the variable nature of carbon, amino acids, as organic compound molecules, may establish a variety of distinct linkages with one another. This allows for the enormous diversity of proteins observed in nature. Because of the roles they serve, they are considered a necessary component in our diet.

(Video) Amino acids - Structure and classification

In this article, we acquired knowledge about the structure, classification, types, and uses of amino acids in detail. Let us use this knowledge for the consumption of food containing the right amount of amino acid.

### FAQs on Amino Acids

Below are the frequently asked questions on Essential Amino Acids:

Q.1. Which foods contain amino acids?
Ans:
Amino acids are obtained from both animal and plant sources. Grains, nuts, seeds, beans, legumes, fruits, vegetables, eggs, milk, cheese, fish, seafood, etc., are foods that contain amino acids.

Q.2. Is it safe to take amino acids every day?
Ans:
Generally, it is safe to use a limited amount of amino acids every day. However, the large dosage of amino acids is harmful. They may lead to abdominal pain, diarrhoea, unhealthy drop in blood pressure, gastrointestinal distress, etc.

Q.3. What are the $$21$$ amino acids?
Ans:
The $$21$$ amino acids are Glycine, Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Methionine, Tryptophan, Proline, Serine, Cysteine, Asparagine, Glutamine, Threonine, Tyrosine, Aspartic acid, Glutamic acid, Lysine, Arginine, Histidine, and Selenocysteine.

Q.4. Do amino acids have side effects?
Ans:
Excess intake of amino acids increases the risk of hypertension, heart disease, fatigue, and loss of contraction.

Q.5. What do amino acids do for your body?
Ans:
Proteins are bodybuilding foods. Amino acids are fundamental building blocks of proteins. Hence, they help in the growth and repair of damaged cells and tissues of the body. Some amino acids are converted into biologically active compounds, e.g., tyrosine is converted into the hormone thyroxine and adrenaline, and also into a skin pigment, melanin.

Q.6. Do amino acids affect kidneys?
Ans:
Amino acids like citrulline and ornithine are actively involved in the urea cycle in the liver. This helps in maintaining the ammonia concentration below toxic levels.

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Study About Essential and Non-Essential Amino Acids

We hope this detailed article on Amino Acids is helpful to you. If you have any queries on this article or in general about Amino Acids, ping us through the comment box below and we will get back to you as soon as possible.

## FAQs

### What is the structural classification of amino acids? ›

Amino acids are classified as basic, acidic, aromatic, aliphatic, or sulfur- containing based on the composition and properties of their R groups.

What is amino acid and classification? ›

“Amino Acids are the organic compounds that combine to form proteins, hence they are referred to as the building components of proteins. These biomolecules are involved in several biological and chemical functions in the human body and are the necessary ingredients for the growth and development of human beings.

What are amino acids simple definition? ›

An amino acid is the fundamental molecule that serves as the building block for proteins. There are 20 different amino acids. A protein consists of one or more chains of amino acids (called polypeptides) whose sequence is encoded in a gene.

What are the four classification of amino acids? ›

There are basically four different classes of amino acids determined by different side chains: (1) non-polar and neutral, (2) polar and neutral, (3) acidic and polar, (4) basic and polar.

What is a structural classification? ›

Structural classification categorizes joints based on the type of. tissue involved in their formations. There are three structural. classifications of joints: fibrous, cartilaginous, and synovial. Of the three types of fibrous joints, syndesmoses are the most movable.

What are the 2 classifications of amino acids? ›

All The 20 amino acids are classified into two different amino acid groups. Essential amino acids and Non-essential amino acids together make up the 20 amino acids. Out of the 20 amino acids, 9 are the essential amino acids, and the others are Non-essential amino acids.

What are the classification of protein? ›

1.1 Classification

Examples are: albumins, globulins, glutelins, albuminoids, histones and protamines. (b) Conjugated proteins. These are simple proteins combined with some non-protein material in the body. Examples are: nucleoproteins, glycoproteins, phosphoproteins, haemoglobins and lecithoproteins.

How are amino acids classified 12? ›

Amino acids can be classified on their solubility in water, if the R group is hydrophilic then the amino acid is water-soluble, or if the amino acid is hydrophobic then the amino acid is water-insoluble. Every amino acid is represented as a three-letter abbreviation and a single-letter symbol.

What is amino acid example? ›

The nonessential amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. Some nonessential amino acids are classified as conditional. This means they're only considered essential when you're ill or stressed.

What is the role of amino acids? ›

Amino acids are required for the synthesis of body protein and other important nitrogen-containing compounds, such as creatine, peptide hormones, and some neurotransmitters. Although allowances are expressed as protein, a the biological requirement is for amino acids.

### What is the definition of amino acid sequence? ›

July 5, 2021. Amino acid sequencing is the process of identifying the arrangement of amino acids in proteins and peptides. Numerous distinct amino acids have been discovered in nature but all proteins in the human body are comprised of just twenty different types.

What are the 4 main components of amino acid structure? ›

The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen. They are particularly important in biochemistry, where the term usually refers to alpha-amino acids. Amino acids serve as the building blocks of proteins, which are linear chains of amino acids.

What are the four main characteristics of amino acids? ›

Amino acids can be classified based on the characteristics of their distinctive side chains as nonpolar, polar but uncharged, negatively charged, or positively charged.

What are the 3 classifications of R groups? ›

Classification: There are basically three major classifications for amino acids (1) those with nonpolar R group, (2) those with uncharged polar R groups, and (3) those with charged polar R group.

What are the 4 types of structures? ›

There are four types of structures;
• Frame: made of separate members (usually thin pieces) put together.
• Shell: encloses or contains its contents.
• Solid (mass): made almost entirely of matter.
• liquid (fluid): braking fluid making the brakes.

What are the 3 classifications of structures? ›

Types of structures. There are three basic types of structures: shell structures, frame structures and solid structures.

Why is it called 2 amino acids? ›

Amino acids are exactly what they say they are! They are compounds containing an amino group, -NH2, and a carboxylic acid group, -COOH. The biologically important amino acids have the amino group attached to the carbon atom next door to the -COOH group. They are known as 2-amino acids.

What are type 2 proteins? ›

Type II membrane protein: This single-pass transmem- brane protein has an extracellular (or luminal) C-terminus and cytoplasmic N-terminus for a cell (or organelle) membrane (Fig. 1b). 3. Multipass transmembrane proteins: In type I and II membrane proteins, the polypeptide crosses the lipid bilayer only once (Fig.

What are 4 types of proteins? ›

The complete structure of a protein can be described at four different levels of complexity: primary, secondary, tertiary, and quaternary structure.

What are the 7 main protein categories? ›

There are seven types of proteins: antibodies, contractile proteins, enzymes, hormonal proteins, structural proteins, storage proteins, and transport proteins.

### What are 20 amino acids? ›

The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The nonessential amino acids are alanine, asparagine, aspartic acid, glutamic acid, and serine.

How are the 20 amino acids classified? ›

All The 20 amino acids are classified into two different amino acid groups. Essential amino acids and Non-essential amino acids together make up the 20 amino acids. Out of the 20 amino acids, 9 are the essential amino acids, and the others are Non-essential amino acids.

What are amino acids 12 chemistry? ›

Amino acids are the compounds whose molecule contains both carboxylix acid (−COOH) groups and the amino (−NH2) group. of the various amino acids , the α-amino acids are most important because they are the building blocks of proteins.

What are the 3 most important amino acids? ›

BCAAs are considered essential because, unlike nonessential amino acids, your body cannot make them. Therefore, it is essential to get them from your diet. The three BCAAs are leucine, isoleucine, and valine. All have a branched molecular structure and are considered essential to the human body.

How do you identify amino acids? ›

All amino acids have an amino group, a carboxyl group, a hydrogen, and an R-group that is unique to the amino acid. In this structure, the R-group is a hydrogen, which corresponds to the amino acid glycine.

What are 5 functions of amino acids? ›

Some of the most important functions of amino acids are as follows:
• Building blocks of proteins. Only L-amino acids are polymerized to form proteins, though both D-amino acids and non-L-amino acids found in nature.
• Biological buffers. ...
• Nitrogen storage. ...
• Formation other compounds.

How amino acid sequence is formed? ›

Each amino acid is delivered to the ribosome by a transfer RNA? molecule depending on the code in the messenger RNA. These amino acids are added in sequence to form a chain of amino acids. After the last amino acid is added to the chain, it folds up to form the final protein.

What is the real definition of sequence? ›

noun. the following of one thing after another; succession. order of succession: a list of books in alphabetical sequence. a continuous or connected series: a sonnet sequence. something that follows; a subsequent event; result; consequence.

What is a sequence simple definition? ›

A sequence of events or things is a number of events or things that come one after another in a particular order.

What are the main parts of amino acids? ›

An amino acid is an organic molecule that is made up of a basic amino group (−NH2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is unique to each amino acid. The term amino acid is short for α-amino [alpha-amino] carboxylic acid.

### What are the 5 elements in amino acids? ›

There are about 20 amino acids, and the atoms most prevalent in these are carbon, hydrogen, oxygen, nitrogen, and sulfur. Each amino acid contains a carboxylic acid end and an amino end.

What are 3 types of amino acids? ›

Amino acids are classified into three groups: Essential amino acids. Nonessential amino acids. Conditional amino acids.

What is the R group called? ›

R is an abbreviation for radical, when the term radical applied to a portion of a complete molecule (not necessarily a free radical), such as a methyl group.

How many protein R groups are there? ›

In the case of the amino acids, there are 20 different R groups, hence, 20 diffrerent amino acids. It is the different R groups that confer the different properties to the amino acids.

› tutorial ›

1.c.i Amino acid Structure: There are basically 20 standard amino acids having different structures in their side chains(R groups) . The common amino acids are ...
Amino acids are the basic components of proteins. Learn about their classification, protein R groups, and why they are essential to life.
We all know that proteins are one of the main building blocks of life. But do you know what are the building blocks of proteins? The basic building blocks of pr...

What are the structural characteristics of an amino acid? ›

Chemically, an amino acid is a molecule that has a carboxylic acid group and an amine group that are each attached to a carbon atom called the α carbon. Each of the 20 amino acids has a specific side chain, known as an R group, that is also attached to the α carbon.

What is the structural property of amino acid? ›

amino acid, Any of a class of organic compounds in which a carbon atom has bonds to an amino group (―NH2), a carboxyl group (―COOH), a hydrogen atom (―H), and an organic side group (called ―R). They are therefore both carboxylic acids and amines.

What is the structural unit of amino acids? ›

The building blocks of proteins are amino acids, which are small organic molecules that consist of an alpha (central) carbon atom linked to an amino group, a carboxyl group, a hydrogen atom, and a variable component called a side chain (see below).

What are the structural characteristics common to all amino acids? ›

All amino acids have the same basic structure, which is shown in Figure 2.1. At the “center” of each amino acid is a carbon called the α carbon and attached to it are four groups - a hydrogen, an α- carboxyl group, an α-amine group, and an R-group, sometimes referred to as a side chain.

What is the structure and function of amino acids? ›

Amino acids are the building blocks of polypeptides and proteins and play important roles in metabolic pathway, gene expression, and cell signal transduction regulation. A single organic amino acid molecule contains two functional groups – amine and carboxyl – and a unique side chain.

### What are the 20 amino acids and their structure? ›

Molecular and linear formulas
Amino acidAbbreviationsLinear formula
AlanineAlaCH3-CH(NH2)-COOH
ArginineArgHN=C(NH2)-NH-(CH2)3-CH(NH2)-COOH
AsparagineAsnH2N-CO-CH2-CH(NH2)-COOH
Aspartic acidAspHOOC-CH2-CH(NH2)-COOH
16 more rows
25 Jun 2001

What is the structural difference between amino acids? ›

There are 20 amino acids that make up proteins and all have the same basic structure, differing only in the R-group or side chain they have. Amino acids are in an equilibrium between two acids with the proton (H+) moving between the amino group and the carboxyl group as shown below.

What is the basic structure of an amino? ›

The general formula of an amino acid is R-CH(NH2)-COOH. Amino acids are known to contain amine and carboxyl functional groups. They also contain a side chain that is made up of an R-group (where 'R' can denote any alkyl or aryl group).

What is the unit of structure? ›

In all life forms, including bacteria, plants, animals, and humans, the cell was defined as the most basic structural and functional unit.

What is the basic unit of structural? ›

A Basic Structural Unit (BSU) is essentially a building block. In anatomy, the basic structural unit of the body is the cell. All living organisms have cells, which start as the zygote — the single cell at the beginning of life, after a spermatazoon fertilizes an oocyte.

What is protein unit? ›

Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein.

What are three properties used to classify amino acids? ›

What are the three properties used to classify amino acids? Nonpolar, polar, and electrically charged are the three properties of side chains used to classify amino acids.

How do you remember the structure of an amino acid? ›

The way to remember their collective structure is CORN, an acronym for the carboxyl group (CO), R group (R), and amino group (N).

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