Explain/teach these concepts to a friend

1. Explain why the Bertozzi group chose sialic acid to label fluorescently.
2. Explain why the azide was chosen as the chemical reporter and why it is considered safe in the context of a larger molecule in biological systems when the chemical sodium azide is not safe.
3. Explain how glycans can be imaged with different colors to compare the trafficking of old glycans versus new glycans.