Nutrient Transport - Advanced Exercise 3

E. coli transports the sugar lactose via the LacY permease—go to the “Transporter: LacY lactose MFS transporter” page: http://biocyc.org/ECOLI/NEW-IMAGE?type=ENZYME&object=LACY-MONOMER

  1. How many amino acids make up this protein, and what is its molecular weight?

  3. How does EcoCyc write out (not a picture!) the transport reaction carried out by LacY? (Hint: The Gene-Reaction Schematic will tell you, if you know how to read the diagram.) Given this transport reaction, what kind of transporter is it? 

  5. What residues in LacY are essential for substrate (lactose) binding and/or proton translocation?

  7. Two residues are important for transport, but are not highlighted in the Sequence Features diagram. What are they, and are they important for the same reason? Explain.

  9. LacI represses lacY transcription; name other regulators that affect  transcription of this gene?

  11. For the dual regulator of the lac operon, how do you explain that the same protein binding to the same site(s) can both activate and repress transcription? Make sure you mention the regulator’s name.

  13. The “Transcription Units” diagram shows a predicted promoter just upstream of lacY, called lacYp. Is this prediction based on experimental evidence? If so, what kind of experiment was done?

  15. Why might this evidence not be considered “high quality” by EcoCyc? (Hint: Look at the lacYp Transcription Unit page.)

  17. Name one other sugar transported by LacY besides lactose. Does the channel have the same affinity for this substrate as lactose?