AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
In prokaryotic cells, DNA molecules are short, circular and not associated…
Full specification wording
DNA, genes and chromosomes: In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.
A prokaryotic cell has no nucleus.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 1 of 11
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A prokaryotic cell has no nucleus. Its DNA lies free in the cytoplasm as a single short, circular molecule, in a region sometimes called the nucleoid. This DNA is not wound around histone proteins, so it is often described as naked. Many prokaryotes also carry plasmids, which are small, separate circles of DNA holding extra genes such as those for antibiotic resistance, but a plasmid is not the cell's main DNA molecule. When the cell divides by binary fission, the circular DNA replicates and a copy passes to each daughter cell. The key features to remember are that the main DNA is short, circular, and not associated with proteins.
What earns the marks
- Prokaryotic DNA is circular and free in the cytoplasm, not enclosed within a nucleus.
- The main DNA molecule is short compared to eukaryotic DNA.
- Prokaryotic DNA is not associated with proteins or histones.
- Plasmids are small, separate circles of DNA carrying extra genes, distinct from the main circular DNA molecule.
Common mistakes and how to put them right
Naming plasmids as the cell's main DNA.
Put it right: Plasmids are small separate circles; the main DNA is the short circular molecule free in the cytoplasm.
Writing nucleosome when nucleoid is meant.
Put it right: Nucleoid is the region containing the main DNA; a nucleosome is DNA wound around histones in eukaryotes.
Stating that a prokaryote contains no protein at all.
Put it right: Say the DNA is not associated with proteins or histones, which is the accepted wording.
Exam tips
- When asked for features of prokaryotic DNA, explicitly state that it is short, circular, and not associated with proteins.
- The phrase 'not associated with proteins' or 'not associated with histones' is the standard way to describe prokaryotic DNA lacking nucleosomes.
Try the lesson
The start of the DNA, genes and chromosomes: In prokaryotic cells, DNA molecules are short, circular and not associated with proteins. lesson, made from checked teaching notes for this specification point.
Have a go first
Which combination of features correctly describes a DNA molecule in a prokaryotic cell?
Listen
A prokaryotic cell has no nucleus. Its DNA lies free in the cytoplasm as a single short, circular molecule, in a region sometimes called the nucleoid. This DNA is not wound around histone proteins, so it is often described as naked. Many prokaryotes also carry plasmids, which are small, separate circles of DNA holding extra genes such as those for antibiotic resistance, but a plasmid is not the cell's main DNA molecule. When the cell divides by binary fission, the circular DNA replicates and a copy passes to each daughter cell. The key features to remember are that the main DNA is short, circular, and not associated with proteins. A strong answer earns marks for these points. Prokaryotic DNA is circular and free in the cytoplasm, not enclosed within a nucleus. The main DNA molecule is short compared to eukaryotic DNA. Prokaryotic DNA is not associated with proteins or histones. Plasmids are small, separate circles of DNA carrying extra genes, distinct from the main circular DNA molecule. A common slip: Naming plasmids as the cell's main DNA. Instead, plasmids are small separate circles; the main DNA is the short circular molecule free in the cytoplasm. Exam tip: When asked for features of prokaryotic DNA, explicitly state that it is short, circular, and not associated with proteins.
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Key words
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circular DNA
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nucleoid region
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DNA without histones
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plasmids
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See every definition
- circular DNA
- The main DNA molecule of a prokaryotic cell is circular and lies free in the cytoplasm, not enclosed within a nucleus.
- nucleoid region
- The region of a prokaryotic cell in which the main DNA lies free in the cytoplasm is sometimes called this.
- DNA without histones
- Prokaryotic DNA is not wound around histone proteins, so it is often described as naked.
- plasmids
- Small, separate circles of DNA holding extra genes such as those for antibiotic resistance, but not the cell's main DNA molecule.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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