Chapter 9, Problem 18STP

Summary Introduction

To describe:

The importance of the spindle fibers to chromatids during prophase.

Introduction:

Cells reproduce by a cycle of growing and dividing called the cell cycle. There are three main stages of a cell cycle; interphase, mitosis and cytokinesis.The second stage is mitosis in which cell’s nucleus and nuclear material divides. There are four stages in mitosis; prophase, metaphase, anaphase and telophase.

Answer to Problem 18STP

During prophase, mitotic spindle fibers form in the cytoplasm. They help in moving and organizing chromosomes before cell division. The spindle fibers attach to the sister chromatids at centromere and then attach to opposite poles of the cell. This arrangement ensures that each new cell receives one complete copy of the DNA.

Explanation of Solution

Prophase is the first stage in which a dividing cell spends most of the time. The nuclear membrane disintegrates and nucleolus disappears. The chromatin tightens and condenses into chromosomes. Chromosomes are shaped like an X. Each half of this X chromosome that was replicated in interphase is called sister chromatid. Mitotic spindle also begins to form between the poles of the cell.The sister chromatids are attached at the center with a structure called centromere. Towards the end of prophase, the spindle fibers attach to the sister chromatids of each chromosome on both sides of the centromere and then attach to opposite poles of the cell. This arrangement ensures that each new cell receives one complete copy of the DNA.