Think About This!
Think about the batteries you use in your toys at home. Let's say you have AA batteries in a toy, you can take those batteries out of your toy and put them in your CD player if you want. You are choosing what to use the batteries for. This is comparable to the alpha peptides that make up the proteins that the body can break down. The body breaks down the protein and chooses how to rebuild the molecules so that it can use them.
On the other hand, you can't take a D battery and use it in an appliance that takes only AA batteries. The appliance won't recognize the batteries, in fact, they won't even fit. This is like the beta peptides. They are a different size, and therefore proteins made up of beta peptides don't get broken down and used for another purpose.