During mitosis, what structure directly generates the forces that move sister chromatids toward opposite spindle poles during anaphase?

• A. Golgi-derived vesicles pushing chromatids by membrane flow
• B. Kinetochore microtubules of the mitotic spindle (with motor proteins and microtubule depolymerization at the kinetochore and/or pole)
• C. Actin microfilaments in the contractile ring
• D. Intermediate filaments pulling chromatids through the nuclear lamina

Answer: (B)

Verified step by step guidance

1. Identify the phase of mitosis in question, which is anaphase, the stage where sister chromatids are separated and pulled toward opposite spindle poles.
2. Recall the main components involved in chromosome movement during mitosis: microtubules (specifically spindle microtubules), motor proteins, and associated structures like kinetochores.
3. Understand that the kinetochore is a protein complex assembled on the centromere of each chromatid, serving as the attachment site for spindle microtubules.
4. Recognize that kinetochore microtubules generate force through two main mechanisms: motor proteins (such as dynein and kinesin) that 'walk' along microtubules, and microtubule depolymerization at the kinetochore or spindle pole, which shortens the microtubules and pulls chromatids inward.
5. Conclude that the structure directly responsible for generating the forces moving sister chromatids during anaphase is the kinetochore microtubules of the mitotic spindle, not Golgi vesicles, actin microfilaments, or intermediate filaments.