Genetic material
Another major difference between the two types of cell is that prokaryotic cells do not have a nucleus or other membrane bound organelles whereas eukaryotic cells do – instead the genetic material of prokaryotes (a single plasmid as opposed to several chromosomes) is in a region of the nucleus called the nucleoid. The genetic material in eukaryotic cells is associated with the histone protein, whereas that of prokaryotic cells is folded around several different proteins including the HU protein. Eukaryotic cells replicate by mitosis and meiosis, whereas prokaryotic cells undergo binary fission. Prokaryotic chromosomes tend to only have one copy of each gene rather than two, so are haploid as opposed to eukaryotic cells’ diploid chromosomes.
Prokaryotic DNA/ RNA lack introns and large non-coding regions between genes, leading to a much more compact genome. However, this means that they do not have gene ‘promoters’ and so they have less control over gene expression. Genes are transcribed and translated to create proteins in groups known as operons rather than as individual genes. These processes occur simultaneously rather than over two locations (the nucleus and ribosomes of eukaryotic cells) since the DNA of prokaryotic cells can interact directly with the cytoplasm.
Membrane bound organelles
Prokaryotic cells usually have no or very few membrane bound organelles – for example they do not have lysosomes, an endoplasmic reticulum or mitochondria. They rarely have a cytoskeleton or microtubules. Instead of having chloroplasts, prokaryotes which photosynthesise have chlorophyll loose in the cytoplasm. In contrast, eukaryotic cells are more complex and have many membrane bound organelles. The mitochondria and chloroplasts or eukaryotic cells are thought to have come from endosymbiotic bacteria, whereas the evolution of prokaryotic cells led to similar processes being carried out over the cell membrane. Prokaryotic cells also have smaller ribosomes and less complex flagella (if present).
Size
Prokaryotic cells tend to be 1-10µm compared to the 10-100µm of eukaryotic cells. The smaller size of prokaryotic cells means that they have a higher surface area to volume ratio, thus allowing substances to diffuse more quickly across the cell – leading to higher metabolic and growth rates and thus a shorter generation time than eukaryotes.
Diagram
A very good diagram illustrating these similarities and differences is below – the top two cells (animal and plant cells) are eukaryotic, whereas the lower bacteria cell is a prokaryote.
This comes from Encyclopaedia Britannica from their website:
Sources
Lecture notes – ‘the living cell’, Michael Akam
Molecular Cell Biology, Sixth Edition
Subtitles are an excellent way to organize your essay, well done ☺
It’s important in compare/ contrast essays to devote equal time and essay space to both the differences and the similarities, this one sentence should not be the extent of the discussion on similarities but looking at the subtitles the reader will think that is the case
This is only true of plant cells- fungi have a cell wall made of chitin.
Prokaryotes do have a separate genome from their plasmids, that’s why horizontal transfer is not deleterious for the donor- the plasmids are independent of their core genome.
Need to briefly define terms like mitosis, meiosis, and binary fission- the essay is meant to show what you know!
Too vague- eukaryotic chromosomes also have only one copy of each gene, but the cell has two copies overall because it has two chromosomes.
Again, need to define these terms so the reader has some context
Should define transcription and translation
Strictly speaking, operon refers to the DNA containing the gene clusters, not the proteins the DNA encodes
But they do have analogs that serve a similar purpose!
Avoid sweeping statements like this- eukaryotes compensate by completing many metabolic reactions across the cristae of the mitochondria, for example, and in certain eukaryotic cells like human muscle cells the metabolic output easily rivals or is higher than the average prokaryote’s.
Too vague! I applaud your use of a figure, but it needs to be more incorporated into your essay- it shouldn’t be there for its own sake.
Overall, you seem to be very good at structuring and organizing your work, so well done! Unfortunately this essay has no conclusion, and neglects to mention that eukaryotes can form multicellular organisms- a huge difference between the two cell types. We will discuss in supervisions how to break down the “need to include” information in your essay plan prior to writing to avoid this in the future. But as a whole, well done!
by
dragonkeeper13 (student)
