Biochemistry Overview & The Aminotransferase Reaction

Hello and welcome back to Educator.com, and welcome back to Biochemistry.0000

Today, we are going to start our discussion of protein and amino acid metabolism and breakdown.0004

Today, I am just going to do a quick overview, talk about the basic reactions, and then, we will start talking about the individual reactions; and, in particular, we are going to talk about this amino transferase reaction.0013

Let's just jump right on in.0024

OK, the proteins that you ingest or the proteins that happen to be inside the cells, anyway, they undergo normal catabolism like anything else.0027

The thing with proteins or the thing with amino acids is they do not just have the carbon skeleton part, they also have that amino group, that NH₃ group or NH₄ group.0040

So, the metabolism happens in 2 ways.0051

The amino group is metabolized, and the carbon skeleton is metabolized.0054

The first thing that we are going to discuss is the metabolism of the amino group, so just a quick breakdown here.0058

We have our proteins from whichever source, and, of course, they are going to be broken down into amino acids.0068

And, so the amino acids, there is one pathway; this is the other pathway here.0078

This becomes NH₄⁺; the amino group is taken away, and this eventually enters the urea cycle.0083

Some of it is used for biosynthesis, this NH₄; the rest of it enters the urea cycle for excretion.0096

Let's go ahead and just put something like that urea there.0103

That is the urea cycle; now, these over here, these are the alpha-keto acids that are left over - OK - what we would call the carbon skeletons without that NH₃ group.0108

OK, and we are going to have...let's go ahead and do...at this point, those are going to enter the citric acid cycle, which we have already discussed, and between them, there is something called the aspartate-argininosuccinate shunt.0125

There is a connection; these amino acids, the amino group is metabolized one way.0161

The carbon skeletons are metabolized another way, and there is a passage between them.0165

This is, sort of, the big picture of what is going on with amino acid metabolism.0172

OK, we are going to talk about this first part right here and in particular, what happens right here; and then, we will go ahead and discuss the urea cycle in subsequent lessons.0177

OK, let's see here.0186

Now, these processes all take place in the liver, in liver cells.0190

What I am about to do here...these processes all take place in the liver.0196

OK, this is going to be the overview here.0212

You know what, let me go ahead and do this in blue, I think.0217

We have C; we have COO.0221

This is R; we have H, and we have our NH₃⁺.0225

This is just some amino acid that is either inside the liver or came from outside from dietary protein- things like that.0230

What happens is the following: C, C, R, O, O^-.0239

I will go ahead and draw this 1, 2, 3, 4, 5, O^-.0250

This is alpha-ketoglutarate, and this is going to be O^- there; and then, we have 1, 2, 3, 4, 5.0256

We have COO^-; we have H.0267

Let me go ahead and put this NH₃⁺ here, CH₂, CH₂, COO^-.0272

This molecule, well, actually, let me go ahead and finish up the drawing here.0279

This is going to be the NH₄⁺.0286

OK, this is going to be excretion, and it is going to be either NH₄⁺.0291

It is going to be urea, or it is going to be uric acid, depending on the particular organism that we are talking about.0299

For us, it is going to be urea; now, let me see here.0307

In red, let me go ahead and do...this is glutamate, this molecule right here.0312

This molecule, right here, is the alpha-ketoglutarate.0321

OK, this is just your any amino acid.0328

Notice that we have an R-group there; it could be anything, and this is your alpha-keto acid that is left over after the amino group is taken off.0333

This amino group is what is taken off; it is transferred to alpha-ketoglutarate, and it is held as glutamate.0341

Glutamate is the central molecule in all of the processes that we are going to be describing that take place in the liver.0350

Glutamate is the place where amino acids are held until they are - I am sorry - further processed.0355

In the process of going from glutamate back to alpha-ketoglutarate, this amino group has released its NH₄.0365

Now, some of these is used for biosynthesis, and the rest is excreted.0373

It enters the urea cycle, which we will discuss in a little bit, so that is all that is going on here.0380

These alpha-keto acids, they are the carbon skeletons that are left over from amino acids that transfer their amino group to alpha-ketoglutarate to form glutamate.0386

OK, that is one of the processes that takes place.0401

OK, now, let's go ahead...another process that takes place is this one.0406

Let's do this one; let’s go back to blue and our molecules.0414

C, C, C, C, C, O^-, H, NH₃⁺, CH₂, CH₂ - oops - 1, 2, 3, 4, 1, 2, 3, 4, 5, yes, there we go.0418

1, 2, 3, 4, 5, yes, here we go, NH₂.0441

This goes to our C, C, C, C, COO^-.0447

This is H; this is NH₃⁺, CH₂, CH₂.0460

This is there, and, of course, NH₄⁺, which goes onto release either the NH₄⁺, the urea or the uric acid.0465

OK, this one, here, we have glutamine.0482

The excess ammonia that is produced in other tissues, tissues that are outside the liver, that ammonia is tied up as glutamine.0490

So, that is this right here; OK, it is tied up that way.0503

What you have is you have glutamate that actually ties it up as the NH₂ group.0508

So, this NH₂ group on the glutamine are the ammonias that are produced by the metabolism of other proteins that are not in the liver cells, and they are transported to the liver cells, at which they give up this particular ammonia group, this NH₂.0512

They give it up as the NH₄, and that goes on to either be used in biosynthesis or excreted as urea, uric acid or NH₄, and this right here, when it gives it up, it turns into this molecule glutamate.0531

And again, as we saw, glutamate is the central molecule in this amino group metabolism.0546

Glutamate- very, very important molecule, and this glutamate, of course, goes on to release this one in another step, which we just saw a minute ago, in its conversion to alpha-ketoglutarate to free up the alpha-ketoglutarate to take more amino groups from other amino acids that are already in the liver.0555

This, right here, is the glutamine from other tissues, OK?0575

OK, now, the excess NH₃ produced in other tissues, as we just said, is tied up as the NH₂ group of glutamine.0584

It is very, very important; it is this NH₂ that is the excess ammonia from other tissues, not this.0613

It is this, which enters the liver and undergoes the above process.0622

Again, glutamate is very, very central here.0650

OK, now, let's take a look at the excess ammonia that is produced in muscle tissue.0654

In this particular case, we have the following; let me go back to blue.0663

We have C, C and CH₃, H, and we have the NH₃⁺, COO^-.0667

This is alanine; OK, this amino acid.0678

The excess ammonia that is formed in muscle tissue is actually tied up with pyruvate to become alanine, and this alanine that is transported to the liver, and it gives up its amino group to form glutamate.0682

This is alanine; actually, I will go back.0701

Let me go ahead and do the... you know what, I am going to erase this, and I am going to do it a little bit lower because I want to do my alpha-ketoglutarate vertically.0706

Let me go ahead and put it over here; this is C, C, C.0715

No, OK, C, C, C, H, OO^-.0720

This is CH₃; this is our NH₃⁺.0730

What we have here is C, C, C, O, O^-.0735

This is that; this is that.0744

Again, another alpha-keto acid; what we have here is the C, 2, 3, 4, 5.0747

This is that one; this is that one.0756

This is CH₂, CH₂, COO^-, and then, of course, we have our glutamate, 1, 2, 3, 4 and 5.0759

We have our carboxylic acid; we have our NH₃ that has been transferred to alpha-ketoglutarate to form glutamate, and let me go ahead and finish these off with a couple of hydrogens and another carboxyl group.0769

OK, now, this is alanine from muscle tissue, OK?0785

OK, the excess ammonia that is formed in muscle tissue is tied up as the amino acid alanine.0798

Alanine is carried to the liver, where it transfers its amino group to alpha-ketoglutarate.0806

This is alpha-ketoglutarate.0812

It transfers its amino to alpha-ketoglutarate, and in the process, it forms glutamate; and now, glutamate can go ahead and do what it does giving up...this is that.0817

In that process of glutamate back to alpha-ketoglutarate, it gives up the NH₃.0829

It gives it up as NH₄, ammonium, and the ammonium is either excreted directly, or it enters the urea cycle to be turned into urea.0834

This alanine, the carbon skeleton of alanine, ends up becoming the pyruvate, and the pyruvate does whatever it does.0842

This is from the alanine.0851

Notice, in all of these transformations of an amino acid to the carbon skeleton, these alpha-ketoacids, this amino group is replaced by a double bonded oxygen, by a carbonyl group.0855

It is called oxidative deamination; Deamination means we remove the N, the nitrogen.0867

The amino group, oxidative means we actually also take away some hydrogens.0872

We take away electrons, and we give them up to oxygen, so the carbon becomes oxidized.0876

It is deaminated, and it is also oxidized, so that is what happens there, again, glutamate, central molecule.0881

OK, now, let's go ahead, and I am going to draw, sort of, a big picture of all three in one place, so that you see that.0890

I am not going to use structures; I am just going to use their names, again, just to get an idea of what is happening here.0900

Let me go back to blue; let's go ahead and put...we have a particular amino acid, whatever amino acid happens to come from intracellular protein breakdown or dietary protein breakdown, and I am just going to go ahead and attach an NH₃ group there.0909