Histones and extra DNA don't make a cell eukaryotic
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a cell has histones or more than one DNA molecule, it must be a eukaryote.”
You first meet histones and stacks of chromosomes in human cells, so they start to feel like eukaryote badges. Some prokaryotes have them too.
The short version
The mistake: If a cell has histones or more than one DNA molecule, it must be a eukaryote.
What's actually true: A eukaryote is defined by its nucleus and other membrane-bound organelles. A feature both groups share can't decide it.
- A eukaryotic cell keeps its DNA inside a nuclear envelope and has other membrane-bound organelles. That's what defines the group.
- A prokaryote usually has one circular chromosome, often with plasmids beside it.
- When a question gives only DNA data, look for several linear chromosomes, each wound around histones. That is the usual eukaryote pattern.
On the exam: Ask whether a membrane surrounds the DNA. Histones and extra DNA molecules show up in prokaryotes too.