Amino Acids — Overview & Structure

(Video) Amino Acids

by Professor Dave Explains

Amino acids are fun little monomers. There are hundreds of them, but humans make all of our proteins out of about 20. In this video, Professor Dave explains what they are, how they differ from each other, and how they come together to form proteins.

These are the 20 amino acids commonly used by humans:

Lysine, arginine, histidine, glutamic acid, aspartic acid, cysteine, tyrosine, threonine, serine, asparagine, glutamine, glycine, proline, alanine, valine, methionine, leucine, isoleucine, tryptophan, and phenylalanine.

Summary of Amino Acids

There are 20 amino acids found in the human body (and in all living things). Different types can have different R groups. The R group determines the chemical and physical properties of the overall molecule.

Amino acids are needed for protein synthesis. They join together to make polypeptide chains. These chains are then folded and modified to make complete, functional proteins.

Essential Vs. Non-essential

There are nine essential amino acids. They are called histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Us humans cannot produce these on our own, so we need to get them from food. That's why they're called essential.

The rest are considered non-essential. That's because our bodies are able to synthesize them from the essential amino acids and other molecules.

What Are Amino Acids?

Proteins are formed from monomers called amino acids joined together by peptide bonds. A chain of these monomers can also be called a polypeptide.

There are 20 amino acids from which all proteins are made. Your body can produce 11 of them on its own. That means we have to get the other nine from the foods we eat.

The nine that we cannot synthesize (make) are called essential amino acids.

Some proteins contain just a few of these monomers in a chain, while other proteins consist of thousands of them. The largest known protein is titin; it's made of a chain of 33,000 amino acids.

Here are the 20 amino acids. Note that many (though not all) have names ending in -ine.

All amino acids have three identical parts: an amino group, a carboxyl group, and a hydrogen. They only differ in their fourth part, called a functional group, R group, or side chain.

In the table above, the functional groups are highlighted in blue. Note how every other part is always the same. The diversity of R groups makes proteins the most diverse of the biological macromolecules.

The Importance of Functional Groups

The functional groups of amino acids are necessary for the creation of all the different proteins our bodies require. Amino acids are usually characterized by their functional groups. Polarity, acidity, and chemical makeup are often used to predict how these functional groups will interact with each other. These interactions determine secondary and tertiary protein structures, which make up the shape of the protein.

Bonding and Polypeptide Chains

Sequences of amino acids, joined together by peptide bonds, form polypeptides. A peptide bond is a covalent bond between the amino group of one amino acid and the carboxyl group of another one. The formation of this bond releases a molecule of water.

The R group doesn't influence the bond formation. This is because peptide bonds only occur between the carboxyl and amino groups. This means that a peptide bond can form between any two amino acids. Their arrangement in a polypeptide is dictated by DNA.

These polypeptide chains are the primary structure of proteins. The interactions between R groups determine further structure.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Monomer}}$ : Any molecule that can react with other molecules of the same or different makeup to form a chain, or polymer

$\color{#8925AE}{\text{Polymer}}$ : A chain of monomers made of a specific type of compound

$\color{#8925AE}{\text{Macromolecule}}$ : A polymer that has a large (macro) molecular mass. There are four main types in organisms: carbohydrates, proteins, lipids, and nucleic acids

$\color{#8925AE}{\text{Amino Acids}}$ : Molecules with a carboxyl group ($-COOH$) and an amino group ($-NH_{2}$). The building blocks of proteins

$\color{#8925AE}{\text{Polypeptide}}$ : A molecule made up of peptide bonds or covalent bonds that hold amino acids together

$\color{#8925AE}{\text{Protein}}$ : Complex polymer made of carbon, hydrogen, nitrogen, and oxygen. They are made of amino acids