Sister chromatids of a metaphase chromosome animation
Date Uploaded: 06/27/2021
Tags: Sister chromatids of a metaphase chromosome how the chromosome is organized centromere loops of DNA histones Nucleosomes
At metaphase, the chromosomes are duplicated and are at their most condensed. In each chromosome. two identical sister chromatids are held together at a constricted region called the centromere. When a chromosome is condensed, interactions among chromosomal proteins keep loops of DNA tightly packed into a "super-coiled" array. On closer examination, we can see that the chromosomal proteins and DNA are organized as a cylindrical fiber. If we immerse a chromosome in saltwater. this fiber loosens up to reveal a beads-on-a-string organization. The string is one molecule of DNA. Each bead is a nucleosome that consists of a DNA molecule looped around a core of histones. Nucleosomes can loosen in controlled ways to give enzymes access to specific DNA regions.
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