A.8.e. <<Previous Problem

To further examine the relationship of Band 3 and spectrin (and more generally, of integral membrane proteins and the peripheral membrane proteins of the cytoskeleton), the markers were “reversed”: that is, the latex bead was attached through the membrane to spectrin and gold was attached to Band 3 proteins. Initially, 3 gold particles are visible in the video sequence (a third one is located on the upper right edge of the ghost).

The video sequence is divided into 3 episodes: 1. during the first 6 sec, the behavior of unmanipulated particles are displayed (and may be compared with your observations in earlier videos); then, the optical tweezers are used to pull the latex particle from right to left at a rate of almost 2 mm/sec; during the final episode, the force field is reversed and the bead is returned more or less to its original location. The video lasts 20 sec and is projected at about the rate it was recorded; therefore the movements you observe are “real time”.

Watch the video in the left compartment, review earlier videos in the right, and consider the questions; then continue to next problem to examine the results of a Control experiment.

QUESTIONS

1. How does Band 3 behavior in the first problem compare with what you observed in the first video in this problem set?

2. What effect, if any, does displacement of spectrin have on Band 3 behavior? How does the effect compare with what you observed when the markers were reversed, in the last experiment?

3. More Band 3 protein markers are evident at the end of the second (and third) episodes than at the beginning. Where do they come from and how do you explain their appearance?

4. How do you think the latex sphere is connected through the membrane to the underlying spectrin?