Amino acid side chain: amino group basic and hydroxyl not?

In summary, the conversation discusses the difference between basicity of molecules with amino group and hydroxyl group attachments. It is explained that nitrogen-containing species are better bases due to the electronegativity of oxygen and its ability to share electrons with H+.
  • #1
Watari
5
0
Hi all

I don't really understand this... How come that if an amino group is attached to the amino acid side chain, like in arginine or lysine, the molecule is basic, but if an hydroxyl group is attached, like threonine, it is not basic?

How come the amino group can accept a H+ and a hydroxyl group cannot?

Thanks
 
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  • #2
Watari said:
Hi all

I don't really understand this... How come that if an amino group is attached to the amino acid side chain, like in arginine or lysine, the molecule is basic, but if an hydroxyl group is attached, like threonine, it is not basic?

How come the amino group can accept a H+ and a hydroxyl group cannot?

Thanks

Ammonia (NH3) is a weak (either Bronsted-Lowry or Lewis definition) base, water (H2O) is a very weak base.

Amines are weak bases (R-NH2), alcohols (R-OH) are very weak bases.

They both can act as bases, but the nitrogen-containing species are better bases. If you want a good explanation for why this is the case, you could say that it is due to the fact that oxygen (0) is more electronegative than nitrogen (0) and wants to hang onto its electrons (not form a bond to H). On the other hand, R-O- has a surplus of electrons (compared with R-OH) , and can share the extra two electrons with an H+ -- why hydroxides, alkoxides are stronger bases.
 

1. What are amino acid side chains?

Amino acid side chains are groups of atoms attached to the central carbon atom in an amino acid. They determine the unique properties and functions of each amino acid.

2. What is the difference between an amino group and a basic side chain?

An amino group (-NH2) is a functional group found in all amino acids, while a basic side chain refers to the specific side chains of amino acids that have basic properties, such as lysine, arginine, and histidine.

3. What is the significance of a hydroxyl side chain in amino acids?

A hydroxyl side chain (-OH) is a functional group found in some amino acids, such as serine and threonine. It can form hydrogen bonds with other molecules and play a role in protein folding and enzyme activity.

4. How does the presence of a basic side chain affect the overall charge of an amino acid?

The presence of a basic side chain in an amino acid makes it positively charged at physiological pH. This can affect the interactions and functions of the amino acid within a protein or in biological processes.

5. Are all amino acids with basic side chains considered essential?

No, not all amino acids with basic side chains are considered essential. Essential amino acids are those that cannot be synthesized by the body and must be obtained from the diet. Some amino acids with basic side chains, such as arginine, can be synthesized by the body and are therefore non-essential.

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