3 key bio 110 - Professor Hinck Bio 110, Fall, problem set...

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

View Full Document Right Arrow Icon
Bio 110, Fall, 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. T/F questions
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.

Page1 / 5

3 key bio 110 - Professor Hinck Bio 110, Fall, problem set...

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