Which of these describes the structure of the endoplasmic reticulum? A. A system of folded membranes
B. A tiny organelle that has. o membrane.
C. a rigid, protective layer found outside the cell membrane.
D. an organelle surrounded by a double membrane containing dna.

You have just sequenced a new protein found in mice and observe that sulfur-containing cysteine residues occur at regular intervals. what is the significance of this finding? it will be important to include cysteine in the diet of the mice. cysteine residues are required for the formation of α helices and β pleated sheets. cysteine residues are involved in disulfide bridges that form tertiary structure. cysteine causes bends, or angles, to occur in the tertiary structure of proteins.