Question

How are spindle microtubules attached to chromosomes?Choose one:

A. The microtubules bind to cohesion complexes on the DNA.
B. The microtubules bind to the kinetochore complexes through a connecting protein.
C. The plus ends of the microtubules bind directly to DNA.
D. The minus ends of the microtubules bind directly to a protein complex on DNA.

Answer 1

Spindle microtubules attach to chromosomes through the kinetochore, a protein structure on the centromere of each chromosome, enabling them to pull sister chromatids apart during cell division.

Step-by-step explanation:

The way in which spindle microtubules are attached to chromosomes is through the kinetochore. The kinetochore is a specialized protein structure located on the centromere of each chromosome. During the stages of prometaphase and metaphase, the spindle fibers, which are composed of microtubules, extend from the microtubule-organizing centers or the centrosomes at the poles of the cell. The plus ends of these microtubules then come into contact and bind firmly to the kinetochores of the chromosomes. These spindle fibers are specifically called kinetochore microtubules. It is through this connection that the microtubules are able to exert force and eventually pull the sister chromatids apart during anaphase. Other types of spindle fibers, such as the polar microtubules, do not bind directly to the chromosomes but instead overlap at the cell's center and contribute to cell elongation.

Answer 2

Spindle microtubules attach to chromosomes at the kinetochore complexes through a connecting protein (option B). The kinetochore is a specialized structure formed at the centromere of each sister chromatid, essential for chromosome alignment and segregation during cell division.

Step-by-step explanation:

Attachment of Spindle Microtubules to Chromosomes

The correct answer to the question “How are spindle microtubules attached to chromosomes?” is B. The microtubules bind to the kinetochore complexes through a connecting protein. During prometaphase, a phase of mitosis, the nuclear envelope breaks down and spindle microtubules grow from microtubule-organizing centers (MTOCs) toward the chromosomes. Each sister chromatid develops a protein structure at the centromere known as a kinetochore, where the spindle microtubules bind. These kinetochore microtubules are essential for aligning chromosomes during metaphase and for their segregation during anaphase, ensuring that each new daughter cell receives the correct number of chromosomes.

In contrast, polar microtubules do not bind directly to chromosomes but overlap and interact with other microtubules from the opposite poles of the cell. These interactions contribute to separating the poles and elongating the cell as chromosomes are segregated.

Hence, the answer is option B.