BL/CH 401 Lecture #4

Amino Acid Structures

General structure of an Amino Acid (abbreviated AA):

{*Figure 1*}

Most Amino Acids are asymmetric or chiral - illustrated here with alanine:

{*Figure 2*}

All Amino Acids found in proteins are in the L-form.

If you were to eat large quantities of D-amino acids, it would kill you.

Types of Amino Acids based on side-chain chemical character:

I. Non-polar or hydrophobic (water hating)

II. Flexible

III. Polar or hydrophilic (water loving)

There are 20 Amino Acids encoded by codons in the genetic code.

(When there are more than 100 AAs found in nature,why only 20 AAs in proteins?
Because these 20 AAs provide all the chemical and size groups needed to make a very large number of proteins.
Plus many of these amino acids become modified after translation into proteins, which increases the available chemical character of amino acid side chains.)

These 20 AAs can be divided into the above 3 groups (non-polar, flexible and polar) and then subdivided by their chemical character:

Non-Polar -- 8 AAs

Hydrocarbon -- 5 AAs -- Ala Val Leu Ile Pro

Aromatic -- 2 AAs --Phe Trp

Thiol Ether -- 1 AA -- Met

Flexible -- 1 AA

Gly -- flexible because it has no side chain

Polar -- 11 AAs

Alcohols -- 3 AAs -- Ser Thr Tyr

Thiol -- 1 AA -- Cys

Amides -- 2 AAs -- Asn Gln

Acids -- 2 AAs -- Asp Glu

Bases -- 3 AAs -- Lys Arg His

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