Phagocytes Produce Transmembrane Proteins Called Toll-Like Receptors (TLR)

Phagocytes produce transmembrane proteins called toll-like receptors (TLR) . The structure of a TLR is represented below. The gray structure indicated by the bracket is _____, which is held together by _____ bonding and is an example of _____.

A) an amino acid; covalent; primary structure
B) beta sheet; hydrogen; secondary structure
C) an alpha helix; hydrogen; secondary structure
D) tRNA; covalent; translation
E) rRNA; covalent; ribosome formation