Biology homework help?

Question

There are 2 questions i am stuck on. Any help would be much appreciated:

1) Amylase digests starch into maltose sugar. It is produced by the pancreas as well as the salivary glands. Suggest why this is necessary.

2) Gastric proteinase is made in the cells of the stomach wall in an inactive form. The enzyme only becomes active once it has been secreted into the stomach acid. Suggest an advantage of this system.

Answer 1

2) The proteinase - as you can see in its name- is an enzyme that helps digest proteins. So if it were to become active before secretion, it would start digesting away the stomach wall itself.

1) I'm not exactly sure how much detail you want for this- or what you mean by "this". But starch needs to be turned into a form of sugar because animals -and humans- cannot store food in the form of starch. (Plants do that-remember potatoes?) Also we get our ATP from sugar- so in any case, starch itself is not of much use to the body.

Answer 2

Starches are long chains of sugars that are bonded together. But they aren't very useful to the body in this form, so amylase is useful as an enzyme that breaks apart the bonds between the sugars (technically these bonds are known as 1,4 glycosidic linkages) to give maltose, which can be used by the body as a source of energy. Maltose is a disaccaride ("two sugar") that is made up of two molecules of glucose. Maltose is further cleaved by enzymes to give two separate molecules of glucose. It is this glucose which is truly useful for the body as energy. The starch from which it originally came must be processed and broken down to maltose.

Many enzymes that act in the stomach require an acidic medium to become active. This is useful because they do not act outside of the stomach medium where such activity may be damaging or not useful (the only place in the body that has very acidic pH is the stomach). One probable reason for this selectivity to pH is that you probably wouldn't want a pepsin like gastric protease to be active in other parts of the body, where it could wreak havoc with any organ (which is made of proteins). In addition, you want the enzyme to be selective so that it acts only when you need it; it would be highy inefficient if the enzyme were active all of the time.