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Comparison with Eukaryotic Cells

In Eukaryotes, linear DNA exists as many chromosomes associated with histone proteins (chromatin) in the nucleus which is enclosed by the nuclear envelope.In Prokaryotes, a circular loop of DNA is free in the cytoplasm, folded and condensed by non-histone proteins.Prokaryotes have small, circular loops of extra-chromosomal DNA in the cytoplasms called plasmids. In eukaryotes, extra-chromosomal DNA is present in mitochondria and chloroplasts.There are no membrane-bound organelles in Prokaryotes.The ribosomes in prokaryotes, mitochondria and chloroplasts are 70S ribosomes and are smaller than the 80S ribosomes found in eukaryotic cells. Both cells have a cytoskeleton, but the cytoskeleton is more complex in eukaryotes.Both eukaryotes and prokaryotes have a cell surface membrane. Prokaryotes have a cell wall made of peptidoglycan, plant cells have a cell wall made of cellulose and animal cells do not have a cell wall.

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Specification: OCR Biology A (H020), AS-level, 2.1.1 Cell structure. Topic: Cell Structure.

Key terms in this lesson

organelle
A membrane-bound structure within a cell with a specific structure suited to a specific function.
mitochondrion
An organelle with a double membrane, the inner one folded into cristae, that is the site of aerobic respiration and ATP production.
cytoskeleton
A network of protein fibres in the cytoplasm that gives cells shape, allows movement and anchors organelles.
plasmid
A small, circular loop of DNA, separate from the main chromosome, found in the cytoplasm of prokaryotic cells.
prokaryotic cell
A cell with no nucleus or membrane-bound organelles, found in bacteria.

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