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M112 F10 STUDY QUESTION SET 2 (FERTILIZATION) ANSWER KEY page 1 It is strongly recommended that you write out your answers to the questions before you look at this key!!! 1A. The binding domain is the region of the protein involved in contact and recognition – it physically interacts with the jelly coat molecule (and must be on the extracellular side of the sperm membrane, so at the N-terminus). Since the response to this binding is species-specific, the binding must be species specific. And specificity in terms of physical interaction must be dictated by structure. In turn, structure is dictated by amino acid sequence (which in turn is encoded by the nucleic acid sequence). We would thus predict that the sequences of the binding domains of the proteins would vary across species. We might see some variation in other regions as well, but these structural differences would not be expected to be reflected in binding differences. 1B. Yes – as noted above, the binding domain should reveal species-specific sequences. And even a few amino acid changes could profoundly affect structure and thus recognition. The rest of the protein is involved in relaying the binding signal to the signal transduction machinery that causes the AR. This signaling function is not predicted to vary much across species, so it is not surprising that these regions of the protein are quite similar across species. 1C. Synthesizing the answers in (A) and (B): The protein recognizes the jelly coat ligand based on a species-specific recognition reflected in the structure (7 aa sequence) of the binding domain. This binding results in the activation of the cytoplasmic domain, triggering the signaling pathway that leads to the acrosome reaction. 1D. The hypothesis regarding species-specific binding focuses on the 7 AAs that vary across species. A direct test of the hypothesis that these 7 AAs dictate species-specific binding is to “swap” the 7 AAs from one species (call it X) into the binding domain of the protein of a second
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This note was uploaded on 11/11/2010 for the course MCDB 112 taught by Professor Staff during the Spring '08 term at UCSB.

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