FI questions -- PAC tranches and Duration understand, collecting, principal, actually

CFA4Techie

Please help to understand two points I've read in the FI topic. Thanks in advance.

1. I saw this statement, "PAC tranches can siphon interest slated for the support tranches, but do not redistribute it. In fact, PAC tranches are designed to provide a minimum guaranteed principal payment by collecting interest targeted for a support tranche when prepayments are low." Does this mean that if prepayments are below expectations, PACs will actually take the interest as well as the principal from support tranches? I thought it was just interest.


2. Please explain why this is true: "Duration and convexity estimates for bonds without embedded options will not be significantly affected by changing the size of the rate shock from 100 basis points to 50 basis points. However, for bonds with embedded options, the size of the rate shock can have a significant effect on the estimates. "