Chocolate cake that really gives you a kick
Posted on 9 December 1999
Biologists call these protein machines 'molecular motors' and the ones in your muscles are called actin and myosin. Eat a mouthful of chocolate cake and your body will break it down into glucose, which in turn is used to make the fuel that allows your muscles to move your arms and legs.
Now scientists at the University of York are studying how the molecules in our muscles actually produce mechanical movement by converting the chemical energy of that chocolate cake. Dr Justin Molloy of the Moelcular Motors Group in the Department of Biology, says: "Rather like a petrol engine, molecular motors take chemical fuel and convert this to mechanical force and movement. Your biceps muscles contain billions and billions of these molecular motors. Our group carries out basic research to try and understand how that engine works, its molecular mechanism. Effectively we are helping to write the engine manual of the human body."
Dr Molloy has developed a novel technique for observing the movements of single molecules with lasers dubbed 'optical tweezers'. Optical tweezers are a form of nanotechnology: they work by using the pressure exerted by light as it is absorbed or refracted by microscopic particles. These forces are so small that you don't even notice them in everyday life. For instance, the force exerted by bright sunlight on your body is about one milligram (the weight of a mosquito). However, a tightly focused laser beam is able to exert enough force to capture and manipulate small particles suspended in fluid; Dr Molloy uses the tiny optical forces to counter-balance those produced by single muscle protein molecules.
In his experiments, a single strand of actin is stretched between two minute plastic beads which are held in place by the optical tweezers. When an immobilised myosin molecule touches the actin filament it breaks down a molecule of fuel and produces a small tug on the actin strand. The size of the tug is measured in nanometres (a millionth of a millimetre) and the force produced measured in picoNewtons (a millionth the weight of a mosquito).
Scientists began studying the mechanism of muscle movement by experimenting with whole muscles, then individual fibres, before moving on to work with single molecules. Recently there have been several key developments in this field including the use of optical tweezers and the imaging of single molecules in solution. These have enabled researchers to provide a better understanding of molecular mechanics. The York group recently discovered that some motor proteins actually produce two mechanical kicks for each molecule of fuel used.
Dr Molloy has just received a grant of £118,000 from the Wellcome Trust to study myosin I, non-muscle motors responsible for intra-muscle force; and a BBSRC grant of £180,000 collaboratively with Dr. Michelle Peckham at Leeds University to study cellular dynamics by visualising single molecules within a living cell.