BRAINCAKEChromosomes
In a eukaryotic cell, the DNA in the nucleus is divided into a number of linear molecules. Each DNA molecule, together with its associated proteins, forms a chromosome.
The DNA is wound around proteins called histones. DNA and histones together form chromatin. For most of the cell cycle the chromatin is spread out through the nucleus so its genes can be transcribed, and individual chromosomes cannot be seen. Before the cell divides, the chromatin coils and condenses, making the chromosomes short and thick enough to be seen with a light microscope.
Before division, each DNA molecule is replicated. The chromosome then consists of two identical copies called sister chromatids, joined at a region called the centromere.
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All 18 lessons in The Cell Cycle · All Edexcel AS-level Biology topics