Amino Acid Metabolism: Introduction

00:01 In this set of lectures, I will describe the most diverse set of metabolic processes that occur that of amino acid metabolism.

00:09 Now to review for just a second, we remember that amino acids are essential for making proteins and that there are 20 common amino acids that are found in all proteins plus an occasional rare one that I will also describe here.

00:22 The structure of amino acids can all be schematically drawn as we see in the figure on the right.

00:27 There's a central alpha carbon that's found and every amino acid has all of these structures that we see here.

00:33 Above it is the hydrogen.

00:34 To the right, an alpha carboxyl group.

00:37 Beneath it, an alpha amine.

00:38 And to the left, an R group, the part of the amino acid that gives every amino acids its characteristics: structure, function and chemistry.

00:47 There's no single pathway for amino acid metabolism, which distinguishes it from some of the other metabolic processes that happen in cells.

00:54 The synthesis pathways for amino acids are actually grouped according to common anabolic precursors that they all have.

01:00 There's a family known as the alpha-ketoglutarate family, a serine family, aspartate acid family, aromatic amino acid family, a pyruvate family, and finally the most complicated pathway, the histidine pathway.

01:14 Now in addition to talking about amino acid metabolism, I will discuss post-translational modification.

01:19 So these are chemical changes that are made to amino acids after they've been built into a protein.

01:25 When we talk about amino acids, we hear the term essential and I want to define what that is.

01:30 So essential amino acids are amino acids that an organism must have in their diet.

01:35 They can't synthesize those.

01:37 Where by contrast, the non-essential amino acids are ones that can be made by an organism.

01:43 Essential versus non-essential varies in humans, and it also varies from one organism to another and also between child and adult.

01:50 So they're not an absolute list.

01:53 One list of essential amino acids and non-essential amino acids for humans is shown here.

01:58 We say for example the ones that have aromatic rings like tryptophan and phenylalanine, we will later discover have common metabolic pathways.

02:06 The tyrosine amino acid which is also an aromatic amino acid can be made from phenylalanine.

02:11 So is tyrosine essential or not essential? Well, if phenylalanine is in the diet, it's not essential.

02:16 If it's not in the diet, it becomes essential.