Show the structures of the following amino acids in their zwitterionic forms: (a) Trp (b) Ile (c

Show the structures of the following amino acids in their...

Key Concepts

Side Chain Functional Groups

The side chains (R groups) of amino acids vary in structure and chemical properties, influencing characteristics such as polarity, hydrophobicity, and reactivity. These variations play an essential role in determining the structure, function, and interactions of proteins.

Amino Acid General Structure

Amino acids are composed of a central (alpha) carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group). This basic structure forms the backbone of proteins and provides the framework for the chemical diversity seen in biological systems.

Zwitterion

A zwitterion is a molecule that contains both positively and negatively charged groups yet remains overall electrically neutral. In amino acids, at physiological pH the amino group is protonated (–NH3?) and the carboxyl group is deprotonated (–COO?), resulting in a dipolar ion structure.

Acid-Base Behavior in Amino Acids

The acid-base properties of amino acids are key to understanding their behavior in solution. The ionization of the amino and carboxyl groups depends on the pH relative to their pKa values, which explains why amino acids exist in zwitterionic form under typical biological conditions.

Transcript

00:01 All right, so we're asked to draw the sphyderionic forms of a couple different amino acid residues.

00:06 The first is triptophen.

00:08 All right, so starting pretty simply with just my amine.

00:17 I'm going to leave an o right there and another oxygen there.

00:21 Now to draw the r group, i'm going to draw one, two.

00:51 All right, so that is triptophen.

00:55 So now we've got to figure out, we've got to worry about sphiderionic form.

00:58 So a sphyderion just means there's basically no charge.

01:02 And the way that's going to do that, like a neutral ph, is this is going to be hydrogenated.

01:08 That is going to be deprotonated, and then you're going to have an h3 plus.

01:15 You'll see that the positive charge on the h3 and the negative charge on the carboxy cancel out to form a neutral ion.

01:22 So this is the sphyterionic form.

01:24 All right, moving on to isocene.

01:28 We're going to have basically the exact same start.

01:32 Nh3 plus.

01:35 I'm going to draw that.

01:37 And then that, just like i would for any other amino acid.

01:42 Now, the reason i immediately just drew nh3 as opposed to waiting to draw the charges is that now that isosine is a hydrocarbon side chain.

01:50 So it's got no charge, no nothing that might affect the overall charge.

01:54 So i can just draw my isoleucine right here like that.

01:58 And that's the form for that one...

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