Abstract
A molecular motor is the nano-scale combustion engine of the cell: it uses a chemical reaction to drive motion. These proteins are fundamental to many cellular processes such as intracellular transport or gene transcription and understanding their behaviour is vital in understanding how we all function. There exist many different types of molecular motor, in this work I am concerned with stepping motors that walk hand-over-hand along a track within a cell. Experiments imply how molecular motors function but in order to describe this precisely one uses the language of mathematics. As motors are small and difficult to observe there is controversy about their movement and thus many competing descriptions, or models, exist. This work focuses on creating and applying general methods to compare the fit to experimental data of different models of the motor myosin-V and its stepping cycles. A review of existing theoretical and experimental work on molecular motors is conducted with emphasis on one type: myosin-V (Chapter 1). Extensions of existing theoretical methods are discussed (Chapter 2) and a novel method for calculating experimentally measurable quantities of molecular motors is presented (Chapter 3). A framework to compare competing models of myosin-V is described in Chapter 4 that allows one to identify mechanisms that enable models to reproduce experimentally observed behaviour. In Chapter 5 a set of models for myosin-V is investigated to establish mechanisms compatible with experimental trends for the average velocity and run length against nucleotide concentration. Asymmetric gating, futile cycling (foot stomping) and a loss of chemical coordination within the molecule are shown to be suitable candidates. In Chapter 6 these ideas are extended to include myosin-V under external forcing. Here multiple substeps, the elastic properties of the motor and slippage along the track are demonstrated to be vital in reproducing important experimental trends.