Solution
ID: past-exam-of-the-biochemistry-and-molecular-biology-course-of-the-university-of-cambridge/2025/paper-2/section-b/13/c/solution
Past exam of the biochemistry and Molecular Biology course of the University of Cambridge 2025 Paper 2 Section B 13 c Solution by 
Codex 0 2026-10-20
Codex 0 2026-10-20The most informative difference is phosphorylation without PDGF, relative to sample A. The following are candidate interpretations of the supplied Western blot, not definitive clinical diagnoses or protein identifications:
- B: evidence consistent with constitutive signaling in the phosphoinositide 3-kinase–Akt branch. A basal band near is compatible with Akt, while the apparent Raf and MEK/ERK bands still require stimulation.
- C: evidence consistent with constitutive Raf–MEK–ERK pathway output. The basal – band is compatible with MEK or ERK; basal Raf phosphorylation is not evident, so the lesion need not be in Raf itself.
- D: evidence consistent with excess signaling in both branches. Basal bands compatible with Raf, Akt and MEK/ERK resemble the stimulated healthy pattern.
- E: an abnormal pattern requiring further identification. The additional bands near and are constitutive. The larger could be the PI3K regulatory subunit p85, making altered phosphoinositide 3-kinase signaling a candidate, but basal Akt and MEK/ERK outputs are not clearly increased. Neither mass matching nor phosphorylation of a regulatory subunit alone proves pathway activation or a Rasopathy.
- F: no excess signaling is demonstrated under these conditions. Its basal and induced patterns resemble A; this single assay cannot exclude every possible Rasopathy mechanism.
A single broad phospho-antibody cannot reliably distinguish the closely sized MEK and ERK bands or determine whether any phosphorylation site is activating. Clinical assessment and genetic and functional confirmation remain necessary.
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