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What is the Chromatin of a Cell?

Cells contain a massive amount of DNA which must be packaged in order to fit into the nucleus. Chromatin consists of a cell's DNA which has been packaged by winding around histone proteins. The structure of chromatin varies throughout the cell's life cycle.

  1. Basic Structure

    • Chromatin is composed of basic units called nucleosomes, which are small sections of DNA wrapped around eight histone proteins that act as a kind of scaffolding.

    Visualizing Chromatin

    • The chromatin in a cell condenses and becomes visible as distinct chromosomes through a microscope during mitosis, when the cell makes a copy of its DNA prior to dividing into two new cells.

    Chromosomes

    • Organisms have different numbers of chromosomes. Humans possess two copies each of their 23 unique chromosomes. Each chromosome represents a portion of the chromatin and contains DNA that codes for different genes.

    Euchromatin and Heterochromatin

    • A single chromosome can contain sections of chromatin that are loosely coiled and transcriptionally active, called euchromatin, or chromatin that is tightly coiled and inactive, called heterochromatin.

    Transcription

    • Cells must constantly transcribe portions of their DNA in order to make necessary proteins. During transcription or DNA replication, portions of the chromatin must remain unfolded in order to allow access to the cell's transcriptional machinery.

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