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

Bases - Positively Charged Amino Acids

Polar -- Charged -- Bases -- Lys (Lysine) -- in computers Lys = K

{*Figure 22*}

Lys has a primary amino group at the end of a 4 Carbon side chain...

and it can be positively charged.

Since the Lys side chain amino group has a high pK (see lecture 3),

it is often charged at biological pH.

Polar -- Charged -- Bases -- Arg (Arginine) -- in computers Arg = R

{*Figure 23*}

Arg has a complex side chain containing 3 Nitrogen groups,

which work as a unit to give a positive charge.

Since the Arg side chain group has a very high pK (see lecture 3),

it is always charged at biological pH.

Arg provides proteins/enzymes with essentially a fixed positive charge.

Polar -- Charged -- Bases -- His (Histidine) -- in computers His = H

{*Figure 24*}

His has an aromatic-like pair of amino groups,

making His a unique AA with a positive charge -- sometimes.

His with a pK for its side chain near neutrality,

means that it can either be charged or not at biological pH.

His, when not charged, is a very strong nucleophile...

and is very important in enzyme chemistry.

His is also very important as a proton acceptor and donor in biochemical reactions.

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

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