Past exam of the biochemistry and Molecular Biology course of the University of Cambridge / 2025 / Paper 2 / Section B / 13 / a

Culture each patient and control sample under matched conditions, including equivalent growth-factor withdrawal where appropriate, then prepare paired unstimulated and PDGF-stimulated samples with the same stimulation time. Rapidly lyse on ice with suitable detergents and protease and phosphatase inhibitors. Measure protein concentration and load equal amounts after SDS-PAGE sample preparation. Separate the proteins with molecular-mass markers, transfer them to a suitable membrane, verify transfer and block non-specific binding. Incubate with the Ras-PST25 primary antibody, wash, add a detectable secondary antibody, wash again and record the signal within its linear range. Preserve the original phosphorylation state and compare equal, verifiably transferred inputs. Include a total-protein loading measure, appropriate antibody controls and independent biological replicates; use matched exposures rather than independently rescaling lanes.