In Order to Test How Sea Urchin Sperm Bind to Eggs

question 45

Multiple Choice

In order to test how sea urchin sperm bind to eggs, scientists isolated the egg receptor protein that binds to the sperm acrosomal protein called bindin. Plastic beads were coated with egg receptor for bindin (ERB1) from eggs of the sea urchin Strongylocentrotus purpuratus, and then the beads mixed with sperm from S. purpuratus or from the related species, S. franciscanus. The researchers counted how many sperm were bound to each bead. The results are shown in the graph below. (Adapted from Kamei and Glabe 2003)
Treatments:
A: S. purpuratus sperm mixed with S. purpuratus ERB1 beads
B: S. purpuratus sperm mixed with beads containing no ERB1 protein
C: S. franciscanus sperm mixed with S. purpuratus ERB1 beads
D: S. franciscanus sperm mixed with beads containing no ERB1 protein
-What is a broader implication from the observations of the experiment?

• A) In sea urchins, fertilisation of eggs by sperm is dependent upon species-specific protein interactions.
• B) Only some species of sea urchins use receptor proteins on their eggs to bind sperm.
• C) Protein-coated plastic beads should not be used to test sperm binding to eggs.
• D) S. franciscanus is probably not a sea urchin, but must be some other type of organism.

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