Selection among replicators and protocell chemotaxis

Thesis

This thesis describes a series of projects which have autocatalysis as the overarching theme.

Chapter 1 is a general introduction to the construction of chemical models of biological systems. There is a discussion of what mechanisms are used to achieve autocatalysis. The biomimetic work of chapters 3 and 4 use lipid replicators, so there is particular focus on the physical autocatalysis of lipid aggregates and their use in prebiotic models. The roles that lipids play in life are used as an illustration of the promise they offer to systems chemists. A brief history of biological homochirality is given.

Two designs for novel asymmetric autocatalytic reactions are described in chapter 2, both based on hydrogen bonding catalysis. Though neither system showed the desired amplification of chirality, this work led to the study of positive nonlinear effects within thiourea catalysis.

Projects which attempt to couple lipid replication with protocell behaviour are presented in chapter 3. In this chapter oil droplets are used as simple model protocells. Interestingly, feedback between the motion of droplets and a lipid forming reaction are observed, with the system showing striking chemotaxis. In the second part of this chapter other systems are used to explore the relationship between lipid formation and compartment division.

Chapter 4 describes observations relating to transient lipid replicators which can be fuelled to be maintained out of equilibrium. An initial finding shows that fuelling can result in dramatic oscillations, as well as stable concentrations. When lipids compete for resources, they typically show a succession through time, an interesting protocell model. Which replicating species dominates results from a multitude of combined effects which cannot be predicted simply using rates of formation of each lipid in isolation.

Finally, chapter 5 outlines the conclusions that can be drawn from these results and what future work remains.

Authors: Scanes, RJH

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: nonlinear effects; Origins of life; lipid world; nonlinear kinetics; asymmetric autocatalysis; protocells; organocatalysis; oscillating reactions; lipid replicators; small molecule replicators; synthetic chemotaxis
• Subjects: Nonlinear chemical kinetics; Chemistry, Organic