How it works
A DNA packaging diagram of the eukaryotic chromosome: five levels in order, from the double helix through nucleosomes and the 30-nanometer fiber to loops and the metaphase chromosome. Read the names first, then press Quiz me.
Read the full guide
Read the levels from the top
DNA is a double helix. It winds around cores of eight histone proteins to make nucleosomes, joined by linker DNA like beads on a string. With histone H1 the beads coil into a fiber about 30 nanometers across. That fiber forms loops, and the loops fold up further. The tightest form is the metaphase chromosome, seen when a cell divides.
What the drawing leaves out
How the loops fold up further into a chromosome is not yet clear. The drawing shows only the levels that two sources name.
- The order runs from thin to thick: helix, beads, fiber, loops, chromosome.
Questions and answers
What are the levels of DNA packaging in order?
The DNA double helix, nucleosomes joined by linker DNA (beads on a string), the 30-nanometer fiber, loops of that fiber, and the fully condensed metaphase chromosome.
What is a nucleosome made of?
A core of eight histone proteins with DNA wound nearly twice around it. Neighboring nucleosomes are joined by linker DNA, and histone H1 sits outside the core.
What does histone H1 do?
It is the histone that is not part of the core. It helps the nucleosomes pack together: the 30-nanometer fiber forms most readily when H1 is present.
Why does DNA need to be packaged?
The DNA of one human cell is about two meters, or six feet, long, and it has to fit inside the nucleus. Winding it around histones and folding it again and again makes it compact.
Can I practice here for “label each level of dna packaging in the eukaryotic chromosome with the appropriate term.”?
Yes, for practice. That sentence is the instruction of a labeling exercise. The drawing here is our own and not a copy of any course figure, so your figure may name a level this one leaves out.