11.   The head of the sperm has proteins that are like specially-shaped keys.

12.   The University of Texas study was based on a comparison of mice which had normal protein FasL activity against mice that were bred to be deficient in this protein.

13.   The viral envelope has different proteins studding its surface, which enable it to bind with human cells and infect them.

14.   Many are malnourished because most corn has little protein.

15.   Some soy milk products do not have sufficient vitamin D for toddlers, and some rice-based milks do not have enough protein.