The present thesis explores some metaphysical issues concerning biochemical kinds and the relations between chemical and biological properties and phenomena. The main result of this thesis is that there is something sui generis about biochemical kinds. This result is motivated by two theoretical steps. The first is characterising biochemical functions as weakly emergent from the chemical structure [Chapter 3, Chapter 6]. The second is via an account for which biochemical kinds are natural categories [Chapter 4, Chapter 7]. The thesis comprises (...) four parts. Part I [Chapter 1, Chapter 2] aims to offer the methodological and conceptual tools that underpin this research. Chapter 1 presents the debate on the unity of science and the motivation of the research. Chapter 2 presents the account of natural kinds that will be used throughout the thesis. Part II [Chapter 3, Chapter 4] offers a detailed metaphysical analysis of the molecular gene. Chapter 3 argues that molecular genes are weakly emergent from nucleic acids. Chapter 4 argues that the category "molecular gene" can be deemed a natural kind, following the account presented in Chapter 2. Part III [Chapter 5, Chapter 6, Chapter 7] explores some of the themes related to biochemical kinds and generalises some of the results from Part II. Chapter 5 considers biochemical functions and how functional attribution should be interpreted for biochemical molecules. Chapter 6 considers the relation between biochemical functions and structure, spelt in terms of weak emergence and explores unity in biochemistry. Chapter 7 considers the topic of biochemical kinds per se and argues that biochemical kinds are natural categories. Part IV [Chapter 8] elucidates the main outcome and the implications that this research can have for future discussion in the philosophy and metaphysics of biochemistry and the unity of science. (shrink)