The parent protein that consists of three protein strands twisted around each other and is secreted by fibroblasts is called what?

The parent protein that consists of three protein strands twisted around each other and is secreted by fibroblasts is called what?

• A. Procollagen
• B. Gelatin
• C. Myosin
• D. Keratin

Answer: (A)

Fibroblasts synthesize a collagen precursor called procollagen, which is made from three polypeptide chains that coil into a triple helix. This precursor is secreted into the extracellular space, where its end propeptides are removed to form mature collagen that then assembles into fibrils. This description—a three-stranded, triple-helix protein that is secreted by fibroblasts—fits procollagen best. Gelatin is simply denatured collagen, not the secreted precursor; myosin is a motor protein, and keratin is a different structural protein, not the secreted triple-helix precursor.

Fibroblasts synthesize a collagen precursor called procollagen, which is made from three polypeptide chains that coil into a triple helix. This precursor is secreted into the extracellular space, where its end propeptides are removed to form mature collagen that then assembles into fibrils. This description—a three-stranded, triple-helix protein that is secreted by fibroblasts—fits procollagen best. Gelatin is simply denatured collagen, not the secreted precursor; myosin is a motor protein, and keratin is a different structural protein, not the secreted triple-helix precursor.