when extracting DNA from a buccal swab, what do the reagents ( chelex
and proteinase k)do, do they/can they effect the result

I don't know about chelex, but proteinase K digests all the proteins
that may have been collected with the sample.  Some of the proteins
could interfere with proteins being used in later processes, others
just make the sample more difficult to work with, or give false
results.

Chelex is often added to crude DNA samples prior PCR to bind
contaminants that could inhibit the PCR reaction. Proteinase K digests
proteins in the sample and bound to the DNA. If you are asking whether
these will affect DNA isolation, the answer is NO. If you are asking
if these can affect tests that are done on the DNA following
isolation, the answer is YES. This is why they are added to eliminate
contaminants and proteins that can interfere with other diagnostic
tests.

when you say thay can affect the tests after isolation do you mean by
the fact that by not adding them problems can happen or that they
themselves can affect the results? can you give an example of a
contaminants and proteins ?

Many Thanks 

Mel xx

Chelex is a scavenger of divalent metal ions that can inhibit PCR, and
therfore is used to promote the reaction.  If you have too much Chelex
in your sample during PCR this can inhibit the polymerase by binding
Mg++ ions. This can be overcome by adding more Mg++ or removing the
Chelex prior to PCR. Proteinase K is largely used to degrade nucleases
that will chew up the DNA, making it unusable.