AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The mitochondria and chloroplasts of eukaryotic cells also contain DNA…
Full specification wording
DNA, genes and chromosomes: The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.
Mitochondria and chloroplasts contain their own DNA, which is structurally similar to prokaryotic DNA: it is short, circular, and not associated with histone proteins.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 4 of 11
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mitochondria and chloroplasts contain their own DNA, which is structurally similar to prokaryotic DNA: it is short, circular, and not associated with histone proteins. These organelles also contain smaller 70S ribosomes and divide by a process resembling binary fission. These shared features support the endosymbiotic theory, suggesting these organelles evolved from free-living prokaryotes engulfed by ancestral eukaryotic cells. While this DNA codes for some organelle proteins, most are coded by nuclear genes. Mitochondrial DNA is typically inherited maternally via the egg's cytoplasm. Consequently, mitochondrial conditions often pass from mothers to offspring, though heteroplasmy can vary the severity.
What earns the marks
- Stating the DNA of mitochondria and chloroplasts is short and circular.
- Specifying this organelle DNA is not associated with histone proteins.
- Noting these organelles contain smaller 70S ribosomes, supporting prokaryotic origins.
- Identifying that mitochondrial DNA is typically inherited maternally via the cytoplasm of the egg.
Common mistakes and how to put them right
Stating these organelles contain no DNA and rely entirely on the nucleus.
Describing mitochondrial or chloroplast DNA as linear, confusing it with nuclear eukaryotic DNA.
Assuming maternal mitochondrial inheritance guarantees all offspring will be equally affected, ignoring heteroplasmy and threshold effects.
Exam tips
- Memorise the three key features shared with prokaryotes: short circular DNA, no histones, and smaller 70S ribosomes.
- If a pedigree shows a trait passing from mothers to offspring but never from fathers, consider mitochondrial inheritance.
Try the lesson
The start of the DNA, genes and chromosomes: The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein. lesson, made from checked teaching notes for this specification point.
Have a go first
Which organelles in a eukaryotic cell contain DNA that is short, circular and not associated with protein?
Listen
Mitochondria and chloroplasts contain their own DNA, which is structurally similar to prokaryotic DNA: it is short, circular, and not associated with histone proteins. These organelles also contain smaller 70S ribosomes and divide by a process resembling binary fission. These shared features support the endosymbiotic theory, suggesting these organelles evolved from free-living prokaryotes engulfed by ancestral eukaryotic cells. While this DNA codes for some organelle proteins, most are coded by nuclear genes. Mitochondrial DNA is typically inherited maternally via the egg's cytoplasm. Consequently, mitochondrial conditions often pass from mothers to offspring, though heteroplasmy can vary the severity. A strong answer earns marks for these points. stating the DNA of mitochondria and chloroplasts is short and circular. specifying this organelle DNA is not associated with histone proteins. noting these organelles contain smaller 70S ribosomes, supporting prokaryotic origins. identifying that mitochondrial DNA is typically inherited maternally via the cytoplasm of the egg. Exam tip: Memorise the three key features shared with prokaryotes: short circular DNA, no histones, and smaller 70S ribosomes.
Key words
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circular organelle DNA
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endosymbiotic theory
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maternal inheritance
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See every definition
- circular organelle DNA
- The DNA of mitochondria and chloroplasts is short, circular and not associated with protein, like the DNA of prokaryotes.
- endosymbiotic theory
- The idea that these organelles evolved from free-living prokaryotes engulfed by ancestral eukaryotic cells, supported by their shared features.
- maternal inheritance
- Mitochondrial DNA is typically inherited maternally via the egg's cytoplasm, so mitochondrial conditions often pass from mothers to offspring.
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