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Section 2 focuses on the interface of biology and chemistry, where we study how the protein folding reaction is impacted by immersion in the crowded intracellular environment and explore whether perturbations to the intracellular folding landscape can be linked to protein function. A review of the forces at play in the intracellular environment and the role that ultra-weak "quinary" interactions play inside living cells is presented in chapter 4, which also includes a review of the most recent literature studying biomolecular dynamics in their native environments. In chapter 5 we study the time-dependence of protein folding inside living cells as probed by live-cell fluorescent microscopy. We find that both the rate of folding and the thermodynamic stability of yeast phosphoglycerate kinase (PGK-FRET) are cell cycle-dependent, a process strictly regulated in time, suggesting that the interplay between the intracellular environment and proteins may impact their function. In chapter 6, a new probe to study protein folding in the cell is explored, namely the GFP/ReAsH Forster resonance energy transfer (FRET) pair. We show that this FRET pair suffers from bleaching artifacts but that directly excited ReAsH is an appealing prospect for studying protein folding in living cells on fast and slow time-scales. Finally, chapter 7 builds on the work presented in chapter 5 and chapter 6 by seeking a protein candidate whose function and in cell folding dynamics are linked. Several constructs of p53, a transcription factor, are explored as potential candidates for answering the question of whether protein activity level indeed can correlate with stability in living cells