Please explain your thinking whether the mutations that cause cancer (stabilize the active form of grass) make the amino acids phenylalanine or glycine.
The correct answer and explanation is:
Correct Answer: Phenylalanine
Explanation (≈300 words):
Mutations that cause cancer by stabilizing the active form of Ras (a small GTPase in the RAS-MAPK signaling pathway) are often associated with phenylalanine, not glycine.
To understand why, we need to look at the RAS protein and its role in cell signaling. RAS switches between an active GTP-bound form and an inactive GDP-bound form. This cycling is tightly regulated. However, mutations in the RAS gene (especially KRAS, HRAS, and NRAS) can disrupt this balance and keep Ras in its active, GTP-bound state, promoting constant cell division — a hallmark of cancer.
One common mutation involves a change at codon 12 (which normally codes for glycine) in the RAS gene. Mutations at this codon often replace glycine with another amino acid, such as phenylalanine, valine, or aspartic acid. When glycine is substituted with phenylalanine, the bulky and hydrophobic side chain of phenylalanine interferes with GTP hydrolysis. This means RAS cannot return to its inactive GDP-bound state, leading to persistent activation of downstream signaling pathways that promote uncontrolled growth and proliferation.
In short:
- Glycine is the normal (wild-type) amino acid in the critical position.
- Phenylalanine is a possible mutation that disrupts Ras inactivation.
- This mutation stabilizes the active form of Ras, contributing to oncogenesis (cancer development).
Therefore, while glycine is the original residue, the mutant form associated with cancer involves phenylalanine (or other amino acids) replacing glycine — and these changes stabilize Ras in its active form.
Summary:
Mutations that cause cancer typically involve glycine being replaced by phenylalanine or other amino acids at a key site in Ras, which stabilizes the active form of the protein. So the correct answer is phenylalanine.