BL/CH 401 Lecture #4 -- Amino Acid Structures

Hydrocarbon NON-POLAR AMINO ACIDS

Non-Polar -- Hydrocarbon -- Ala (Alanine) - in computers Ala = A

{*Figure 3*}

The chiral Carbon of Ala is emphasized here!

All amino acids are derivatives of Ala, except Gly (see below).

Non-Polar -- Hydrocarbon -- Val (Valine) - in computers Val = V

{*Figure 4*}

Val has to methyl groups added to Ala to make an isopropyl group.

Non-Polar -- Hydrocarbon -- Leu (Leucine) - in computers Leu = L

{*Figure 5*}

Leu adds an isopropyl group to Ala so that Leu has 4 carbons in its side chain.

Non-Polar -- Hydrocarbon -- Ile (Isoleucine) - in computers Ile = I

{*Figure 6*}

Ile is a structural isomer of Leu so it also has 4 carbons in its side chain.

But Ile is bulkier than Leu near the base of the side chain,

while Leu is bulkier than Ile farther out on the side chain (size/shape of side chains is important).

Ile has a 2nd chiral center which is emphasized in the Ile drawing above (Fig. 6).

Why does Ile have a chiral center and Leu not?

Non-Polar -- Hydrocarbon -- Pro (Proline) - in computers Pro = P

{*Figure 7*}

Pro is a very special amino acid due to its inflexible character!!!

Pro is inflexible because its side chain bonds to alpha-amino group

in a ring structure which can not twist around the bond between

alpha-amino group and alpha carbon, which all other AAs can.

Also Pro, thus, has a secondary amino group (notice the single hydrogen on its Nitrogen atom)

with different chemical character than the primary amino groups in all other amino acids,

which have two hydrogens on them.

Try to draw Pro or make a model if you have a model set (left over from a chemistry course).

©Wilbur H. Campbell, 1995, 1996; wcampbel@mtu.edu

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