What Are Amino Acid Functional Groups? (2023)

So you've heard of amino acid functional groups and you want to understand them better. This article will help to clarify the structure of amino acids, their functional groups, and what it all has to do with the creation of protein.

Some Basic Reference Definitions

Below are the names of the 20 common amino acids in the body, nine of which are essential amino acids, meaning humans must eat or otherwise consume them to get what we need to function. The essential aminos are designated with an asterisk (*). There are their names, their three-letter codes, their one-letter codes (as used in drawing models of molecular bonds), plus their bond type and properties. Polar vs. nonpolar bond types refers to their covalent bonds. We will start with those definitions for the bond type category—get ready for some high school clique metaphors to help you visualize all this organic chemistry.

Covalent Bonds

Covalent bonds form the base of the chemical reactions between atoms of different elements. The bonds form in only one way: when an electron becomes shared by two elements. That creates the connection that then results in a new substance. Covalent bonds can exist as polar or nonpolar compounds, and all bonds that are polar or nonpolar in nature are by definition covalent.

To visualize: think of these bonds like the bonds of friendship. Two students (atoms) come close to one another and share their lunch (electrons). This sharing means there is a bond of friendship (the covalent bond). Whereas before they had been two separate elements, strangers, now a new substance has formed: a friendship.

Polar Bonds

Polar bonds are bonds where the electrons are not shared equally between two atoms. These types of bonds are what designates polar molecules from nonpolar ones. This occurs when the two atoms bonding are from two different elements; atoms from the same element do not form polar bonds.

Just as bigger planets can hold bigger moons in their orbits, so it is with atoms: they pull electrons to the best of their ability, but when they come into the orbit of a better puller (a bigger planet), that atom will pull more electrons into its orbit (and steal the lesser planet's moons).

(Video) Functional groups | Properties of carbon | Biology | Khan Academy

When two atoms of the same element meet, neither is stronger than the other, and thus neither one is more attractive than the other regarding electrons, and so neither side exhibits the polar pull, and the bond is considered nonpolar. The negative charge end of the bond is the more attractive atom, because it can draw more negative (-) electrons.

To put this back into the context of our high school friends, let's say the two atoms meeting and bonding are a vivacious theater student and a more reserved math student. In sharing lunch, somehow the theater student always gets more to eat because the math student is so transfixed and feels the need to be overly generous. This is true whenever the theater student meets someone with less personal magnetism, which means the theater student gets an overabundance of food (electrons), which is negative because the increased calories may cause the theater student to gain weight, or get a bad complexion from eating too much processed lunch food. Eventually the theater student will fill up to the brim with extra food, and won't be able to accept any more.

Nonpolar Bonds

A nonpolar bond is formed when two atoms from the same element meet and share electrons equally and evenly with one another. Neither atom is a better electron puller than the other, and so there is no one side more polar than the other.

In our friendship metaphor, this is a bond between two theater students, or two math students, who pool all of their lunch food together in the middle of the table, and pull from the pile equally and in unison.

Hydrophobic vs. Hydrophilic

For the properties category, hydrophobic and hydrophilic refer to molecules and their reactions to water. Molecules that repel water, or are phobic of hydration, are hydrophobic. The molecules that can form an ionic or hydrogen bond with a water molecule are hydrophilic, they have a philia for water, they like the feel of it.

If atoms are students once again, the hydrophilic ones are either on the swim team itself, or part of a group that likes to swim and heads out to the beach or the lake every weekend. The hydrophobic ones either can't swim or simply do not like it. Hydrophobic students will tell you that their friends and the community pool go together like oil and water: they don't mix.

(Video) Amino Acids

Your Amino Acids: Names and Designations

Amino-acid name: AlanineAmino-acid name: Arginine
Three-letter code: Ala

One-letter code: A

Bond type: Nonpolar

Properties: Hydrophobic

Three-letter code: Arg

One-letter code: R

Bond type: Polar, positively charged

Properties: Hydrophilic

Amino-acid name: AsparagineAmino-acid name: Aspartate
Three-letter code: Asn

One-letter code: N

Bond type: Polar, no charge

Properties: Hydrophilic

Three-letter code: Asp

One-letter code: D

Bond type: Polar, negatively charged

Properties: Hydrophilic

Amino-acid name: CysteineAmino-acid name: Glutamate
Three-letter code: Cys

One-letter code: C

Bond type: Nonpolar, no charge

Properties: Hydrophobic

Three-letter code: Glu

One-letter code: E

Bond type: Polar, negatively charged

Properties: Hydrophilic

Amino-acid name: GlutamineAmino-acid name: Glycine
Three-letter code: Gln

One-letter code: Q

Bond type: Polar, no charge

Properties: Hydrophilic

Three-letter code: Gly

One-letter code: G

Bond type: Nonpolar, no charge

Properties: Hydrophobic

Amino-acid name: Histidine*Amino-acid name: Isoleucine*
Three-letter code: His

One-letter code: H

Bond type: Polar, positively charged

Properties: Hydrophilic

Three-letter code: Ile

One-letter code: I

Bond type: Nonpolar

Properties: Hydrophobic

Amino-acid name: Leucine*Amino-acid name: Lysine*
Three-letter code: Leu

One-letter code: L

Bond type: Nonpolar

Properties: Hydrophobic

Three-letter code: Lys

One-letter code: K

Bond type: Polar, positively charged

Properties: Hydrophilic

Amino-acid name: Methionine*Amino-acid name: Phenylalanine
Three-letter code: Met

One-letter code: M

Bond type: Nonpolar

Properties: Hydrophobic

Three-letter code: Phe

One-letter code: F

Bond type: Nonpolar

Properties: Hydrophobic

Amino-acid name: ProlineAmino-acid name: Serine
Three-letter code: Pro

One-letter code: P

Bond type: Nonpolar

Properties: Hydrophobic

Three-letter code: Ser

One-letter code: S

Bond type: Polar, no charge

Properties: Hydrophilic

Amino-acid name: Threonine*Amino-acid name: Tryptophan*
Three-letter code: Thr

One-letter code: T

Bond type: Polar, no charge

Properties: Hydrophilic

Three-letter code: Trp

One-letter code: W

Bond type: Nonpolar, no charge

Properties: Hydrophobic

Amino-acid name: TyrosineAmino-acid name: Valine*
Three-letter code: Tyr

One-letter code: Y

Bond type: Polar, no charge

Properties: Hydrophobic

Three-letter code: Val

One-letter code: V

Bond type: Nonpolar

Properties: Hydrophobic


It's a lot of information, to be sure, but it's provided as a reference point to help facilitate the following explanations.

What Are Amino Acid Functional Groups?

Amino acids are all made up of groups of atoms, and the functional groups are the important ones in each amino, it's what makes them different and unique, deciding whether the amino overall is polar or nonpolar, acidic or basic.

Each of the above standard 20 aminos have one hydrogen atom, and two groups attached to its alpha carbon atom: an amino or amine group (~NH3+) and a carboxyl group (~COOH). They are each then distinguished from other types of amino acids by their third attached functional group: side chains referred to as R groups. When you ask what are amino acid functional groups, here they are, with the R group being the one with the most diversity. When you think of R groups, think R for radical, as it's the variable part that makes each amino acid different from the rest.

What Are Amino AcidFunctional Groups? (1)

About R Groups

Of the 20 standard amino acids that make up the building blocks of protein:

  • 6 of them have hydrocarbon R groups
  • 7 of them have neutral R groups
  • 6 of them have acid or base R groups

The simplest of the amino acids is glycine, which has just one hydrogen atom in the position of the side chain group (no R group at all, just an attached loner).

(Video) Amino functional group explained!

Some Quite Interesting Relevant Facts

  • In chemistry, organic compounds are generally thought of as any chemical compound that contains carbon, which includes amino acids.
  • All amino acids are soluble in an aqueous solution (water), even the hydrophobic ones (counterintuitive but true).
  • All naturally occurring amino acids are in the L-form; L for levorotatory, referring to the way you'd turn the amino acid to read the order of its attached groups (the opposite of is dextrorotatory or D-form).
  • As you can see in the above list, 50% of the amino acids have nonpolar side chains. The other half is designated polar, five of which have side chains that are not only polar, but charged.
  • Because the carboxyl group is an acid, it can form peptide bonds with the base amino groups of other amino acids, causing chemical reactions that create polypeptide chains and amino acid residues.
  • When two amino acids react and form a peptide bond, and that process goes on to be repeated, many amino acids may string together, which forms a protein structure.
  • This protein synthesis (though a little more complicated than just linking acid to base over and over again like links of a chain) is among the most fundamental of biological processes, an invaluable component of every cell. Proteins make our nails and hair, protein builds and repairs our tissues, protein is needed to make our hormones, our enzymes, and many other chemicals in the human body.
  • In 1953, Stanley Miller and Harold Urey conducted a simulation, to test a hypothesis about how life originally formed on Earth. They built a closed system that contained a heated pool of water under a mixture of gases that were thought to be present in the early atmosphere of Earth. They delivered an electric current to simulate lightning, and after a week analyzed the contents of the liquid pool. In there they discovered that several organic amino acids had spontaneously formed from inorganic raw materials. This leant support to the theory that the first life on Earth arose out of the primordial ooze through naturally occurring chemical reactions like a little flash of lightning.

Conclusion

The functional or R groups of amino acids are the groups that define the chemistry of proteins. They are the basis on which amino acids are classified, and according to the Miller-Urey experiment, possibly the start of all organic life on Earth. Not only is "What are amino acid functional groups?" a stimulating question to ask, but the answer to that question comes awfully close to revealing the true answers behind life, the universe, and...well...everything.

Ready to start reaping the benefits of these amino acids? Learn how they can help your health now!

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(Video) Amino Acids: Polar vs Non-Polar, Acidic, Basic, and Neutral

FAQs

Where are the functional groups of amino acids? ›

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.

How many functional groups are there in amino acids? ›

There are 2 functional groups in an amino acid. The two functional groups in an amino acid are an amino group (NH2) and a carboxyl group (COOH).

How do you identify an amino functional group? ›

The amino group is one of several nitrogen-containing functional groups found in organic molecules. What distinguishes the amino group is that the nitrogen atom is connected by single bonds to either hydrogen or carbon.

What are the 4 main functional groups? ›

Amino groups can pick up hydrogen ions from the surroundings, so they make molecules basic. Other functional groups include sulfhydryl, carbonyl, methyl, and phosphate groups.

What are the 5 main functional groups? ›

Some of the important functional groups in biological molecules include: hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl groups.

Do amino acids have different functional groups? ›

Generally, an amino acid will have two different functional groups: an amino group and a carboxyl group.

How do you define a functional group? ›

A functional group is defined as an atom or group of atoms within a molecule that has similar chemical properties whenever it appears in various compounds. Even if other parts of the molecule are quite different, certain functional groups tend to react in certain ways.

What is a functional group and examples? ›

Functional groups are specific groupings of atoms within molecules that have their own characteristic properties, regardless of the other atoms present in a molecule. Common examples of functional groups are alcohols, alkenes, alkynes, amines, carboxylic acids, aldehydes, ketones, esters, and ethers, among others.

What are the three functional groups in all amino acids? ›

The three functional groups that make up an amino acid are the amino group, the carboxyl group, and the R group. Amino acids are joined together to form chains called polypeptides.

How do you remember the 7 functional groups? ›

Mnemonics for Functional Groups
  1. Vowels: Remember the vowels "A", "E", and "Y" for Alkane, Alkene, and Alkyne. ...
  2. Alcohol: Look for the "C-O-H" in "Alcohol."
  3. Ether: Ethers were anesthetics used in the 1800s. ...
  4. Amine: Remember the "N" stands for nitrogen.
  5. Aldehyde: This sounds like "Adelaide," the Australian city.

What functional groups are in proteins? ›

Protein residues contain four major functional groups; the Amine group, the hydrogen group, the carboxyl group and the R (which can be any of the different types of amino acids) group.

Why are the functional groups of an amino acid important? ›

Amino acids are all made up of groups of atoms, and the functional groups are the important ones in each amino, it's what makes them different and unique, deciding whether the amino overall is polar or nonpolar, acidic or basic.

Why is it called a functional group? ›

What is called a functional group? Functional groups are groups of one or more atoms with distinctive chemical properties regardless of what is attached to them. The atoms of functional groups are bound by covalent bonds with one another and with the rest of the molecule.

What is the difference between functional group and? ›

In organic chemistry, the terms functional group and substituent are often found. The key difference between functional group and substituent is that a functional group is an active part of a molecule whereas a substituent is a chemical species that can replace an atom or a group of atoms in a molecule.

What functional group is NH2? ›

NH2 as a functional group is also called a primary amine. This is the case when the group has one bond to the compound. If the group has 2 bonds to a compound, it will have the formula NH and be considered a secondary amine.

What is the role of functional groups? ›

Functional groups are important in chemistry because they are the portion of a molecule that is capable of characteristic reactions. They, therefore, determine the properties and chemistry of many organic compounds. An organic compound is any compound that contains carbon and another element.

Where are functional groups located? ›

Functional groups are found along the “carbon backbone” of macromolecules which is formed by chains and/or rings of carbon atoms with the occasional substitution of an element such as nitrogen or oxygen. Molecules with other elements in their carbon backbone are substituted hydrocarbons.

Where are amino groups found? ›

Amine functional groups are found in a wide variety of compounds, including natural and synthetic dyes, polymers, vitamins, and medications such as penicillin and codeine. They are also found in many molecules essential to life, such as amino acids, hormones, neurotransmitters, and DNA.

Where are functional ribosomes located? ›

Ribosomes are found 'free' in the cytoplasm or bound to the endoplasmic reticulum (ER) to form rough ER. In a mammalian cell there can be as many as 10 million ribosomes. Several ribosomes can be attached to the same mRNA strand, this structure is called a polysome.

What is meant by functional group? ›

A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds.

What's meant by functional group? ›

functional group, any of numerous combinations of atoms that form parts of chemical molecules, that undergo characteristic reactions themselves, and that in many cases influence the reactivity of the remainder of each molecule.

How many amino groups are there? ›

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.

How many functional groups are there? ›

What are the four functional groups? In biological molecules, some of the essential functional groups include hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl groups. These groups play a significant role in forming molecules such as DNA, proteins, carbohydrates, and lipids.

Why are functional groups important? ›

Functional groups are important in chemistry because they are the portion of a molecule that is capable of characteristic reactions. They, therefore, determine the properties and chemistry of many organic compounds.

What is functional group in easy way? ›

A functional group is defined as an atom or group of atoms within a molecule that has similar chemical properties whenever it appears in various compounds. Even if other parts of the molecule are quite different, certain functional groups tend to react in certain ways.

What organelle makes proteins? ›

The endoplasmic reticulum can either be smooth or rough, and in general its function is to produce proteins for the rest of the cell to function. The rough endoplasmic reticulum has on it ribosomes, which are small, round organelles whose function it is to make those proteins.

Who discovered proteins? ›

Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the Swedish chemist Jöns Jacob Berzelius in 1838.

What is the functional site of a protein? ›

Protein functional sites are amino acid residues, or groups of residues, that perform functional roles in proteins. Examples of functional sites include catalytic sites in enzymes, ligand-binding sites for small molecules, metal ions, nucleic acids and other proteins and protein–protein interaction sites.

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