Analyses highlighting the epistemic dimension of students' participation in science have dominated science education literature for the past several years. While most of this literature has focused on how students learn together, the relational nature of these knowledge-building interactions has been under-examined. In response, this paper empirically examines how these epistemic interactions are also relational. Building upon Noddings' ethic of care and Maheux and Roth's argument that "being-in-the-know" in mathematics is always "being-in-the-know-with" others, I develop the construct of "relationality" as a moral and ethical orientation to teaching that is also visible in moment-to-moment interaction. I present a micro-interactional analysis of what enacting relationality can look like in the context of science teaching through two excerpts in which 8th grade students made unexpected bids to shift their participation. I illustrate how these relationally- and epistemically-entangled bids, and the teachers' attention and responses to them, precipitated role negotiations: explorations and expansions of what it could mean to "be-in-the-know-with" while building science knowledge. This analysis suggests that learning to notice students' bids for new roles and learning to interpret those bids as simultaneously relational and epistemic moves is an essential aspect of responsive teaching that cultivates trusting relationships as participation in sophisticated disciplinary practices. I conclude with a discussion of how micro-level relational dynamics function as a mechanism by which meso-level classroom cultures and macro-level social narratives are constituted and contested, and the implications of these constitutions and contestations for science, teachers, and science teacher education.