BRAINCAKENucleoid
Prokaryotic cells have no nucleus. Instead, their main DNA is found in an irregular region of the cytoplasm called the nucleoid. The nucleoid is not surrounded by a membrane, so the DNA is in direct contact with the cytoplasm and its ribosomes.
The nucleoid contains a single, large, circular chromosome made of double-stranded DNA. In Escherichia coli, for example, the chromosome is about 4.6 million base pairs long and carries over 4000 genes. Stretched out, it would be roughly 1000 times longer than the cell itself, so it has to be tightly packed. The DNA is supercoiled (twisted on itself) and folded into loops held by proteins. Prokaryotes do not wrap their DNA around histones in nucleosomes as eukaryotes do.
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Key terms in this lesson
- intron
- A non-coding sequence within a gene that is removed from the pre-mRNA by splicing before translation.
More in Prokaryotic Cells
- Bacterial Cell
- Pili and Flagella
- Cell Surface Membrane
- Plasmids
- 70S Ribosomes
- Gram-Staining
- Antibiotics
- Alternative Classification of Bacteria
All 31 lessons in Prokaryotic Cells · All Edexcel AS-level Biology topics