Enzymes

[Muska]

Argh. Firstly apologies if this is in the wrong forum (I usually end up managing to post stuff in the wrong forum, it’s not deliberate- honest!)

I need help with enzymes. Or rather, I need some sort of enzyme for dummies advice.

I understand what enzymes do, and how they break down molecules. After that I get a bit lost.

What I am trying to do is create an enzyme for dummies table, so I can explain it in laymans terms, but I get lost when it comes to monosaccharides, polysaccharides etc.

My table fields consist of: Enzyme (ie Pepsin) Substrate (ie carbs / starch) Substrate group (ie disaccharides) Location (ie stomach) and resul (ie pepides)

Is this right? I have been trying to get my head around this for days, and the more I read the more I confuse myself. Can anyone help?

[JackBean]

What are laymans terms? What are you actually asking for or about?
The fields seem fine, but your examples do not belong into one row.

[Swede]

If you by "pepides" meant "peptides" I think you had better change that to monosaccharides or disaccharides. You could also change the "substrate group"-example to polysaccharides. Pepsin acts on polysacharides to make mainlu disaccharides. Peptides are amino acids bound together, and has nothing to do wth carbohydrates.

[Muska]

laymans terms- simplified or easier to explain. Ie I don’t want to get into too much depth because my understanding is minimal, and I’m not a biology studen but rather a psychology student who has taken an extra biology module to better understand the bodies physiology.

I have to give a presentation on friday explaining the digestive system however, and although I have now developed a reasonable understanding on most of the digestive system, the more I read on enzymes the more I confuse myself.

For example carbohydrates are divided into 3 groups- disaccharides, monosaccharides, polysaccharides. I’m reading the aim is to break disaccharides and polysaccharides into monosaccharides, but that confuses me as I’m also reading that carbs, ie starch, need to be broken down into maltose. But maltose is a result of a substrate, whereas monosaccharides are a substrate- so how can a substrate (monosacharides) be brokwn down into…well, monosaccharides?? Does that make sense? And am I understanding it all wrong?

What do you mean my examples do now belong in one row? I’m trying to make the table from scrach based on my readings and understandings, but can’t quite formulate the basic (emphasis on basic here!) table categories I need.

[Muska]

quote Swede:

If you by “pepides” meant “peptides” I think you had better change that to monosaccharides or disaccharides. You could also change the “substrate group”-example to polysaccharides. Pepsin acts on polysacharides to make mainlu disaccharides. Peptides are amino acids bound together, and has nothing to do wth carbohydrates.

See this is where I get confused. My understanding is that peptides (sorry typo in first post!) are the result of a substrate being broken down by an enzyme, but polysaccharides etc are actual substrates?

[JackBean]

Swede: pepsin is protease!
http://en.wikipedia.org/wiki/Pepsin

Muska: OK, you need to acount, that in the body there is both anabolism (building up) and catabolism (break down). Also, if you want something to break down, you have first to build that, right? So, basically everything can be both substrate as well as product, but of different enzyme (there are thousands of enzymes!).

I mean, that pepsin has nothing to do with saccharides, so its substrate is some polypeptide and product some oligopeptide.
On the other hand, amylase (enzyme (everything ending in English with -ase is enzyme; everything ending with -ose is sugar/saccharide;)) breaks down amylose (see, polysaccharide) to smaler units like oligosaccharides and monosaccharides.

[Muska]

quote JackBean:

Swede: pepsin is protease!
http://en.wikipedia.org/wiki/Pepsin

Muska: OK, you need to acount, that in the body there is both anabolism (building up) and catabolism (break down). Also, if you want something to break down, you have first to build that, right? So, basically everything can be both substrate as well as product, but of different enzyme (there are thousands of enzymes!).

I mean, that pepsin has nothing to do with saccharides, so its substrate is some polypeptide and product some oligopeptide.
On the other hand, amylase (enzyme (everything ending in English with -ase is enzyme; everything ending with -ose is sugar/saccharide;)) breaks down amylose (see, polysaccharide) to smaler units like oligosaccharides and monosaccharides.

Ha this is like trying to grab smoke with my hands at the moment. Just as I think I am beginning to understand it it slips through my fingers!

I understand pepsin has nothing to do with saccharides, as they are a group of carbs- right? Pepsin is an enzyme that breaks up protein, where as amaylase breaks up carbs- ie dissacharides and polysaccharides etc?

Ok if I approach it like this:
Location: Mouth. Enzyme: Amylase: Substrate: carbs- mainly starch (Disaccharides and
Polysaccharides??): Result: maltose (and monosaccharides???)

Is that right?

Location: Stomach. Enzyme: Pepsin: Substrate: Protein Result: polypeptide?

Also I understand the enzyme Pepsin belongs to the peptidase group of enzymes, so is there a group that amylase belongs to? Or is amylase the group, and in actual fact the specific enzymes have other names?

And by the way- I really, really appreciate all the help as I can appreciate how hard this muct be to explain to someone who has no clue!

[JackBean]

There is hierarchical classification of the enzymes:
http://www.chem.qmul.ac.uk/iubmb/
So, amylase belongs to hydrolases called glycosylases, called glycosidases. The first name tells you, that it hydrolyse bonds, i.e. breaks bond by adding water. The other names tell you the specificity (towards sugars).

As you can see on the wiki article about amylase, there are several types differing in the specificity. But these are isoforms and amylase is taken as one enzyme (i.e. as is pepsin).

[Muska]

Ah right ok, it’s starting to make sense.

Ok would I be right in saying that in the stomach, the enzyme Pepsin (belonging to the enzyme group peptidase) breaks down the substrate protein into peptides. These then pass into the duodenum where the peptides now become the substrate? So the amylase trypsin (enzyme group hydrolases??) in the s.intestine breaks down the substrate peptides into…something…?

[mamoru]

quote Muska:

Ah right ok, it’s starting to make sense.

Ok would I be right in saying that in the stomach, the enzyme Pepsin (belonging to the enzyme group peptidase) breaks down the substrate protein into peptides. These then pass into the duodenum where the peptides now become the substrate? So the amylase trypsin (enzyme group hydrolases??) in the s.intestine breaks down the substrate peptides into…something…?

I think you are confused with your terminology.

Peptides are essentially proteins (really any amino acid polymer, so doesn’t have to be functional like a protein or enzyme). So, a peptidase will be an enzyme which breaks down other proteins (by breaking the peptide bonds between amino acids). Pepsin and Tripsin are both peptidases, so they will act to break down peptides. The ultimate end of this is breaking the peptide down into individual amino acids (since amino acids are the monomers of a peptide).

Amylase does not act on peptides. The substrate for amylase is polysaccharides which are carbohydrates. The ultimate end of this is usually to break polysaccharides (multi-unit sugars) down to monosaccharides (single unit sugars).

Anyway, for your example, you could say that Pepsin breaks large proteins down to smaller manageable peptides. These then travel to the small intestine and are broken down further (all the way down to individual amino acids?) by trypsin.

Amylase won’t be involved with this because it is breaking down starch, either in your mouth (there is amylase in your saliva) or in your intestine, as amylase doesn’t work in the low pH of the stomach.

[Muska]

Ok that actually all made sense. I think maybe I am trying to be too reductionist and group it all into an easy to read table consisting of set categories, like enzyme, substrate, result etc when really it doesn’t quite work like that. (unfortunately!) Or at least it does but there are so many enzymes etc and substrates that it is a pointless task.

I understand amylase doesn’t work on proteins, as I see enzymes working like jigsaw pieces in that they only fit certain shaped/sized substrate molecules, so the substrate for amylase is carbs.

But you’re right, all the terminologies confused me. I saw monosaccharides, disaccharides and polysaccharides etc as simply being different types of starch that needed to be broken down into maltose. But it’s not- starch is a polysaccharide, a type of carbohydrate. Maltose is a disaccharide. So both maltose and strach effectively need to be broken down into a monosaccharide?

Can a polysaccharide be broken down straight to a monosaccharide? Or does it have to be broken down to a disaccharide, then a monosaccharide? and if so am I right in saying if starch enters the mouth, it is broken down into maltose first? Or is that just a massive generalisation, and not necessarily true?

[mamoru]

quote Muska:

But you’re right, all the terminologies confused me. I saw monosaccharides, disaccharides and polysaccharides etc as simply being different types of starch that needed to be broken down into maltose. But it’s not- starch is a polysaccharide, a type of carbohydrate. Maltose is a disaccharide. So both maltose and strach effectively need to be broken down into a monosaccharide?

Essentially yes. The final monosaccharide will be glucose (C6H12O6). Maltose is a disaccharide of 2 glucose molecules. Starch is a polysaccharide of many glucose molecules.

quote :

Can a polysaccharide be broken down straight to a monosaccharide? Or does it have to be broken down to a disaccharide, then a monosaccharide? and if so am I right in saying if starch enters the mouth, it is broken down into maltose first? Or is that just a massive generalisation, and not necessarily true?

I’m not entirely sure. But, generally speaking (and as far as I understand it, though I may be incorrect on the specifics), amylase acts to break down starch into maltose. Then maltase (another enzyme) can break maltose down into glucose. So, you essentially have have amylase in the mouth starting to break down long (several hundred unit) starch molecules into smaller pieces. These then pass through everything to the small intestine where amylase continues to break it down to maltose. Maltase can then break it down to glucose. The reason for going through all of that is that larger polysaccharides, such as starch, cannot travel across the membranes of the small intestine and into the blood. Glucose (and maybe maltose?) can, and it can then be carried by the blood to wherever it needs to go (usually the liver where it is taken up and stored as glycogen, which is another polysaccharide, but also to any body cells that need some glucose to burn for energy).

[Muska]

So amylase breaks polysaccharides into disaccharides in the mouth. This disaccharide (in the form of maltose) travles through to the small intestine where maltese breaks the disaccharide into monosaccharide (glucose)?

Do you know how disaccharides reach the small intestine? I assume it isn’t through the alimantary canal?(though I could be wrong!)

[JackBean]

1) proteins are (poly)peptides, you can’t say it vice versa.

Muska (BTW where did you get your nick?:)
all the main components of our food are polycondensates. That means, that they are made of smaller units (amino acids in proteins; monosaccharides in carbs; fatty acids and glycerol in lipids; nucleobases and sugar-phosphate backbone in NA), which are connected by bond, made by release of water. So, when you want to break these big molecule, you add water to the previously mentioned bond and this does hydrolase in general. It hydrolyses any bond. Amylase hydrolyse glycosidic bond in carbs, pepsin hydrolyses peptide bond in polypeptides.

Look to the wiki page for Amylose
http://en.wikipedia.org/wiki/Amylase#Classification
here you can see, that there are several kinds of them differing in substrate specificity. Alpha breaks the chain in middle releasing oligosaccharides (having several Glc monomers connected), Beta cuts it from the end thus producing Glc

[Muska]

Ahh polypeptides that does actually sort of answer another question I had- are polypeptides broken down into peptides? And then into amino acids? Or are polypeptides and peptides in reality the same thing? Are there ‘dipeptides’? Or have I just made that word up?

I’m going to be honest, much of that wiki link is lost on me. I understand the very basics of enzyme breakdowns, but when you start going into ‘Glc’ and the such I get lost. I’m not really a biology student, I’m just taking a sort of biology for beginners module at uni to better understand the biological side of my psychology degree! fortunately I’m not quite as inept when it comes to psychology…!

Ha my name comes from a skateboarder named Chad Muska. When I was younger I used to skate and had Chad Muska’s siganture deck, so a few people started calling me Muska and it kind of stuck ever since.

[JackBean]

No, dipeptides exist, as well as tripeptides, tetrapeptides etc.

All these molecules (saccharides, peptides, nucleotides), you can divide to mono-; oligo- and poly-
Mono is clear, that’s only one
Oligo are "few", usually 2-10
Poly are many
Usually, there is little difference between polypeptides and proteins, that proteins are bigger (I think from 10 kDa?), but that can vary…

So, polyPEPTIDES are peptides, composed of many amino acids and they are broken down to smaller poly or oligopeptides (or single amino acids can be cleaved off from the terminus)

[Muska]

Ok I now understand what you all have been trying to explain to me for the last 2 days. (By understand I mean understand on a very basic level!) But I have managed to put it into my powerpoint presentation- huzzah! And better, I know what enzymes are for and what saccharides etc are so hopefully I won’t get caught out by the tutor! (A week ago I had never even heard of an enzyme, nevermind polypeptides and disaccharides etc!)

Honest to God if I hadn’t have come here I would still be buried neck deep in biology books trying to get my head around the whole concept (although if I had really thought about it- the clues are in the names poly/di/mono etc.) so I owe everyone who has offered me advice here massively. I really do.

Kudos for keeping patient with me as I fumbled my way around molecular biology 101 though, really is much appreciated.

[Author]

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