DNA in a loop
No nucleus? The DNA lives in the nucleoid.
A cell with no nucleus
Bacteria have no well-defined nucleus. But they still have DNA.
Where do you think a bacterium keeps its DNA?
What this lesson covers
The idea
Prokaryotic cells have no well-defined nucleus; their DNA is a single circular molecule associated with proteins, lying in a region called the nucleoid.
A cell with no nucleus
Bacteria have no well-defined nucleus. But they still have DNA.
Where do you think a bacterium keeps its DNA?
- Lying free in a region of the cell
- In a nucleus with a double membrane
- It has no DNA
Where is the DNA?
Look at each kind of cell and find its DNA.
The nucleoid
Prokaryotic cells have no well-defined nucleus. Their DNA is a single circular molecule associated with specific proteins. The region containing this genetic material is called the nucleoid.
Nucleoid means “nucleus-like”. It is a region, not a membrane-bound nucleus.
- Prokaryotic cell | Eukaryotic cell
- Where is the DNA? | in the nucleoid | in the nucleus
- Shape of DNA | single circular molecule | in chromosomes
- Membrane around DNA? | no | yes
Notes
Prokaryotic cells have no well-defined nucleus. Their DNA is a single circular molecule with proteins, in a region called the nucleoid.
Check yourself
The region of a prokaryotic cell that holds its DNA is the…
The DNA of a prokaryotic cell is…
Is the nucleoid surrounded by a nuclear membrane?
Which cell has a nucleoid?
- nucleoid — correct. Yes.
- nucleus. That is the membrane-bound structure of eukaryotic cells.
- vacuole. Vacuoles store water and other materials.
- a single circular molecule with proteins — correct. Yes.
- many rod-shaped chromosomes in a nucleus. That describes eukaryotic cells.
- absent. Every cell has DNA.
- No — correct. Yes. That is why prokaryotic cells have no well-defined nucleus.
- Yes, a double membrane. That is the nucleus of eukaryotic cells.
- Yes, a single membrane. The nucleoid has no membrane.
- A bacterial cell — correct. Yes. Bacteria are prokaryotic.
- A plant cell. Plant cells have a nucleus.
- A human cell. Human cells have a nucleus.