8 - Into the membrane

Summary

Be like a duck. Calm on the surface, but always paddling like the dickens underneath.

(Attributed to Michael Caine, British actor, born 1933)

GENERAL IDEA

In this chapter we encounter some key examples of single molecules and molecular complexes which are primarily integrated into the cell membrane performing a range of essential biological functions, and of the surrounding molecular architecture of the phospholipids, that have been studied extensively using exemplary single-molecule biophysics techniques

Introduction

Roughly 30% of all proteins are integrated into the membranes of cells, a significant proportion which is indicative of the importance of molecular processes which occur at the surfaces of cells. The cell membrane is an enormously important structure. It provides a physical support for seeding a vast array of complex surface chemistry reactions, as well as acting as the site for molecular detectors, pumps, channels and motors, not to mention its obvious function as a physical boundary to the cell. In the previous chapter, we discussed some of the important biological systems that deal with molecules and molecular complexes which spend significant periods outside the cell membrane boundary, and how single-molecule methods have dramatically improved our understanding of these processes. In this chapter, we will discuss several of the biological systems which are primarily associated directly with the cell membrane itself, and how single-molecule techniques have probed many of these in physiologically relevant settings, including both protein complexes integrated into the membrane and the makeup of the phosopholipid bilayer. These include molecular complexes which transport molecules across cell membranes, such as ion channels and protein transport nanopores, as well as some remarkable molecular machines which are involved in cell motility and cellular fuel manufacture.