PS3KEY

PS3KEY - Professor Hinck Bio 110, problem set 3 1) Order...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Professor Hinck Bio 110, problem set 3 1) Order the molecules on the following list according to their ability to diffues through a lipid bilayer, beginning with the one that crosses the bilayer most readily. Explain your answer. 1. Ca++ 2. CO 2 3. Ethanol 4. Glucose 5. RNA 6. H 2 O 1ANS) The order is CO2 (small and nonpolar) > ethanol (small and slightly polar) > H2O (small and polar) > glucose (large and polar) > Ca2+ (small and charged) > RNA (very large and highly charged). This list nicely illustrates the two basic properties that govern the capacity of molecules to diffuse through a lipid bilayer: size (small > large) and polarity (nonpolar > polar > charged). 2) K+ channels typically transport K+ ion 10,000 times better than Na+ ions, yet these two ions carry the same charge and are about the same size (0.133 nm for K+ and 0.095 nm for Na+). Briefly describe how a K+ channel manages to discriminate against Na+ ions. 2ANS) The key feature of a K+ channel is its selectivity filter. For the bacterial K+ channel, whose three-dimensional structure is known, the selectivity filter is a short, rigid, narrow pore, which is lined by carbonyl oxygens from the polypeptide backbone. The carbonyl groups are spaced exactly to accommodate a K+ ion, allowing it to shed its water molecules and interact with the oxygen atoms of the carbonyls. By contrast, the oxygen atoms are spaced slightly too far apart to accommodate a Na+ ion, providing too little binding energy to make up for the loss of water molecules that must be shed to pass through the filter.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/06/2012 for the course BIO 110 taught by Professor Rexach during the Fall '08 term at UCSC.

Page1 / 5

PS3KEY - Professor Hinck Bio 110, problem set 3 1) Order...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online