What Are Amino Acids? - Definition & Structure

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  • 0:01 Definition & Structure
  • 0:42 Side Chains
  • 1:06 Types of Amino Acids
  • 2:10 Lesson Summary
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

Your body cannot function without proteins, and in order to build all these important proteins, your body needs amino acids. In this lesson, learn what amino acids are and what they look like. Then test your new knowledge with a short quiz.

Definition and Structure

The human body has thousands of different proteins, all of which are necessary for staying alive and healthy. Amino acids are the building blocks of proteins. There are 20 different amino acids in nature. All amino acids include five basic parts:

  1. a central carbon atom
  2. a hydrogen atom
  3. an amino group - consisting of a nitrogen atom and two hydrogen atoms
  4. a carboxyl group - consisting of a carbon atom, two oxygen atoms, and one hydrogen atom
  5. an R-group or side chain - consisting of varying atoms

Side Chains

The R-group (side chain) is what makes each amino acid unique. Each of the 20 amino acids has a different side chain structure. Side chains contain mainly hydrogen, carbon, and oxygen atoms. Some amino acids have sulfur or nitrogen atoms in their R-groups.

Each amino acid has a name, abbreviation, and unique side chain make-up.

Amino Acid Abbreviation R-group Linear Formula
Alanine Ala CH3
Arginine Arg HN=C(NH2)-NH-(CH2)3
Asparagine Asn H2N-CO-CH2
Aspartic acid Asp HOOC-CH2
Cysteine Cys HS-CH2
Glutamic acid Glu HOOC-(CH2)2
Glutamine Gln H2N-CO-(CH2)2
Glycine Gly H
Histidine His NH-CH=N-CH=C-CH2
Isoleucine Ile CH3-CH2-CH(CH3)
Leucine Leu (CH3)2-CH-CH2
Lysine Lys H2N-(CH2)4
Methionine Met CH3-S-(CH2)2
Phenylalanine Phe C6H5-CH2
Proline Pro (CH2)3
Serine Ser HO-CH2
Threonine Thr CH3-CH(OH)
Tryptophan Trp C6H4-NH-CH=C-CH2
Tyrosine Tyr HO-C6H4-CH2
Valine Val (CH3)2-CH

Types of Amino Acids

Some amino acids are considered essential amino acids, which are amino acids that our body cannot make on its own. We must get essential amino acids from the foods we eat. Nonessential amino acids are amino acids that our bodies can synthesize regardless of what we eat. To help you remember, you can think 'it is essential that I eat food with essential aminos!'

In humans, there are ten essential and ten nonessential amino acids. However, arginine is kind of a special case. Adults can synthesize arginine, but infants cannot. So arginine is an essential amino acid only for babies.

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