Can someone please help me with these chemistry questions

Question

1. Describe in detail the use of SDS and dithiothreitol in SDS-PAGE. What is the purpose of these reagents and how do they contribute to the analysis?
2. What does High Affinity refer to when in the analytical column of Ion Chromatography and what affects this?

Answer 1

SDS coats the analyte molecules and make them uncoil. They therefore have properties of movement proportional only to their length. Dithiothreitol snips (reduces) any S-S bonds between two segments of chains on proteins, so that they can uncoil to full length. If proteins were coiled up, they would not have usefully different transport properties through the gel column -- in fact, they would probably stick and that would be that. But uncoiled, they are like trying to pour cooked spaghetti through a strainer -- yes, it will eventually go through, but it takes a lot of water to persuade it! Whereas, short snippets of spaghetti go right through. Same with proteins. Separation on the basis of length -- shorter come out first.

-- Cheers, --mr. d.