DNA in Prokaryotes and Eukaryotes
All cells use DNA, but they do not organise it in the same way. Prokaryotes package DNA for fast cell function and gene exchange, while eukaryotes organise DNA into linear chromosomes inside a nucleus.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions — start at whatever level suits you.
A student says, "DNA is just DNA, so it should be stored the same way in every organism. A bacterium should have chromosomes in a nucleus just like a human cell."
Before reading on, explain what you think is wrong with that statement. How might DNA organisation differ between a bacterium and a human cell, and why could that matter biologically?
Know
- How DNA is organised in prokaryotes and eukaryotes.
- The difference between circular DNA, plasmids and linear chromosomes.
Understand
- Why nucleus and nucleoid are not the same thing.
- How chromatin packaging helps fit DNA into eukaryotic cells.
Can Do
- Compare bacterial plasmids with human chromosomes in a precise HSC-style response.
- Link DNA organisation to cell function and biotechnology use.
Core Content
Syllabus focus · same molecule, different arrangement
The DNA molecule itself is still a double helix, but the way that DNA is arranged inside cells differs between organism types.
In this lesson, the key idea is not that prokaryotes and eukaryotes use different kinds of hereditary material. Both use DNA. The important comparison is how that DNA is stored, packaged and organised inside the cell.
Prokaryotic cells usually contain one main circular DNA molecule located in the nucleoid region. Eukaryotic cells usually contain multiple linear DNA molecules packaged into chromosomes inside a membrane-bound nucleus.
What to write in your book
- Both cell types use DNA (a double helix) — only the arrangement differs.
- Prokaryotes: one main circular DNA molecule in the nucleoid.
- Eukaryotes: multiple linear chromosomes in a membrane-bound nucleus.
- Use precise terms: circular DNA, linear chromosomes.
Both prokaryotes and eukaryotes use _____ as their hereditary material (type the molecule's abbreviation).
Prokaryotic DNA · nucleoid · plasmids
Most prokaryotes, such as bacteria, do not have a nucleus. Their main chromosome is typically a circular DNA molecule located in the nucleoid region of the cell. The nucleoid is not surrounded by a nuclear membrane.
Many prokaryotes also contain plasmids, which are small circular DNA molecules separate from the main chromosome. Plasmids often carry extra genes, for example genes associated with antibiotic resistance. Because plasmids are separate from the main chromosome, they are important in both natural bacterial gene transfer and biotechnology applications.
What to write in your book
- Prokaryotes have no nucleus; main DNA = circular, in the nucleoid (no membrane).
- Plasmids = small circular DNA molecules separate from the main chromosome.
- Plasmids carry extra genes (e.g. antibiotic resistance) and aid gene transfer.
- Plasmids ≠ the main chromosome.
Small circular DNA molecules separate from the main bacterial chromosome are called:
Eukaryotic DNA · packaging into the nucleus
Eukaryotic cells, such as plant and animal cells, contain DNA inside a membrane-bound nucleus. Their DNA is arranged as multiple linear chromosomes rather than one main circular chromosome.
Eukaryotic DNA is associated with proteins. When the DNA is less condensed, it is referred to as chromatin. During cell division, this chromatin condenses into visible chromosomes. This organisation allows large amounts of DNA to fit into the nucleus while still remaining accessible when genes need to be used.
Genes occupy specific positions on chromosomes, so chromosome organisation matters for inheritance and later for gene expression.
What to write in your book
- Eukaryotes: DNA inside a membrane-bound nucleus, as multiple linear chromosomes.
- DNA + proteins = chromatin (less condensed form).
- Chromatin condenses into visible chromosomes during cell division.
- Packaging fits large DNA into the nucleus while keeping genes accessible.
Eukaryotic DNA is arranged as a single circular chromosome floating in the cytoplasm.
Prokaryotic DNA is typically a single circular chromosome located in the nucleoid region.
Eukaryotic and prokaryotic DNA both associate with histone proteins to form nucleosomes.
Comparison · description, gene transfer, biotechnology
Differences in DNA organisation affect how we describe cells, how genes are transferred, and how biotechnology uses DNA. A bacterial plasmid can be isolated and used as a vector. A human chromosome cannot be treated as if it were a small circular DNA ring.
Prokaryotes
- Main DNA usually circular
- Located in nucleoid, not nucleus
- Often have plasmids
- Useful in gene-transfer biotechnology
Eukaryotes
- DNA arranged as multiple linear chromosomes
- Located inside nucleus
- Packaged with proteins as chromatin
- Organisation supports complex gene regulation
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Main DNA form | Usually one circular chromosome | Multiple linear chromosomes |
| Location | Nucleoid region | Nucleus |
| Additional DNA | Often plasmids present | No equivalent plasmid role in typical HSC comparison |
| Packaging | Less extensive than eukaryotic chromatin packaging | DNA associated with proteins as chromatin |
What to write in your book
- Prokaryotes: circular DNA, nucleoid, plasmids → useful in gene-transfer biotech.
- Eukaryotes: linear chromosomes, nucleus, chromatin → complex gene regulation.
- A plasmid can be a vector; a human chromosome cannot be used the same way.
- Know the comparison table: form, location, additional DNA, packaging.
Where is the main DNA of a prokaryotic cell located?
Both cell types use DNA, but the form, location and packaging differ.
Model · four quick reference points
Bacterial DNA
Usually a single main circular chromosome in the nucleoid, with possible plasmids.
Human DNA
Multiple linear chromosomes inside a membrane-bound nucleus.
Chromatin
Eukaryotic DNA associated with proteins before full chromosome condensation.
Biotech Link
Plasmids are useful vectors because they are separate, replicating DNA molecules.
Activities
Compare and Represent
Complete these statements.
1. The main DNA of a bacterium is usually ____ and located in the ____.
2. Additional small circular DNA molecules in some bacteria are called ____.
3. In a eukaryotic cell, DNA is found inside the ____ and arranged as ____ chromosomes.
Link Structure to Use
Explain why plasmids are useful in biotechnology, but why a full human chromosome would not usually be used in the same way as a simple bacterial plasmid.
Core idea
- Prokaryotes and eukaryotes both use DNA, but they organise it differently inside cells.
Mechanism / structure
- Prokaryotes usually have circular DNA in a nucleoid and may contain plasmids. Eukaryotes have linear chromosomes in a nucleus, packaged as chromatin.
Common mistake
- Do not say that bacteria have a nucleus or that plasmids are the same as the main chromosome.
Exam sentence starter
- "DNA in prokaryotes differs from DNA in eukaryotes because it is usually..."
A fresh set drawn from this lesson's question bank — feedback shown immediately. +5 XP per correct · +25 XP all correct
Pick your answer, then rate your confidence — that tells the system what to drill next.
UnderstandBand 3(3 marks) 1. Outline two differences between DNA organisation in prokaryotic and eukaryotic cells.
AnalyseBand 4(4 marks) 2. Explain why chromatin is an important concept when describing eukaryotic DNA.
EvaluateBand 5–6(5 marks) 3. Evaluate the statement: "Plasmids are a useful example of how DNA organisation in prokaryotes can support biotechnology applications."
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1 — Compare and Represent
1. circular DNA molecule; nucleoid.
2. plasmids.
3. nucleus; linear.
Activity 2 — Link Structure to Use
Plasmids are useful because they are small, separate circular DNA molecules that can carry inserted genes and replicate inside bacterial cells. A full human chromosome is far larger, organised differently, and not used in the same simple vector role as a bacterial plasmid.
Short Answer Model Responses
Q1 (3 marks): In prokaryotes, the main DNA is usually circular and located in the nucleoid rather than a nucleus [1]. In eukaryotes, DNA is arranged as linear chromosomes [1]. Eukaryotic DNA is enclosed inside a membrane-bound nucleus, unlike prokaryotic DNA [1].
Q2 (4 marks): Chromatin refers to eukaryotic DNA associated with proteins [1]. This packaging helps fit large amounts of DNA into the nucleus [1]. It also allows DNA to exist in a less condensed form when genes need to be accessed [1]. During cell division, chromatin condenses into visible chromosomes [1].
Q3 (5 marks): The statement is valid because plasmids show that prokaryotic DNA organisation includes small DNA molecules separate from the main chromosome [1]. Plasmids are circular and can replicate inside bacterial cells [1]. They are useful in biotechnology because inserted genes can be carried on plasmids into bacteria [1]. This makes plasmids practical vectors for gene transfer and cloning applications [1]. Therefore plasmids are a strong example of how prokaryotic DNA organisation supports biotechnology use [1].
Prokaryotes
Usually one main circular DNA molecule in a nucleoid, plus possible plasmids.
Eukaryotes
Multiple linear chromosomes inside a nucleus.
Chromatin
DNA associated with proteins in eukaryotic cells.
Exam trap
A nucleoid is not a nucleus, and a plasmid is not the main chromosome.
Rapid-fire questions on circular DNA, plasmids, the nucleoid, linear chromosomes and chromatin. Beat the boss to bank a tier — gold (perfect + fast), silver (80%+), or bronze (cleared).
You should now be able to reject the idea that all organisms store DNA the same way. DNA is still DNA, but its cellular organisation differs sharply between prokaryotes and eukaryotes, and those differences matter in cell biology and biotechnology.