Which structure is the site of attachment for spindle fibers on chromosomes during prometaphase?

Which structure is the site of attachment for spindle fibers on chromosomes during prometaphase?

• A. Centromere
• B. Kinetochore
• C. Chromatin
• D. Chromatid

Answer: (B)

Spindle microtubules attach to kinetochores on the chromosomes during prometaphase. A kinetochore is a protein structure that forms at the centromere of each chromatid, serving as the actual attachment point for microtubules. This connection lets the chromosomes be pulled toward opposite poles and maneuvered toward the cell's center for alignment at the metaphase plate. The centromere is simply the region that holds sister chromatids together, not the attachment site itself. Chromatin is the DNA-protein complex that makes up chromosomes, and a chromatid is one of the two identical copies after DNA replication. Because the kinetochore is the specialized structure that directly interfaces with spindle fibers, it is the correct site of attachment.

Spindle microtubules attach to kinetochores on the chromosomes during prometaphase. A kinetochore is a protein structure that forms at the centromere of each chromatid, serving as the actual attachment point for microtubules. This connection lets the chromosomes be pulled toward opposite poles and maneuvered toward the cell's center for alignment at the metaphase plate. The centromere is simply the region that holds sister chromatids together, not the attachment site itself. Chromatin is the DNA-protein complex that makes up chromosomes, and a chromatid is one of the two identical copies after DNA replication. Because the kinetochore is the specialized structure that directly interfaces with spindle fibers, it is the correct site of attachment.