🗻 Big Picture: What's the difference between us and bacteria? Well, a lot of things, but they all come down to the major division between prokaryotes (them) and eukaryotes (us). Find out what sets us apart at the cellular level in this guide!
All living things are made up of cells. They can be as small as a diatom (which has one cell), or as big as a blue whale (which has 100 quadrillion cells) (yes, we said quadrillion) (no, we didn’t know that was a real number until today). Cells fall into one of two categories: prokaryotic or eukaryotic. But who cares, right? A cell’s a cell. Well, not necessarily. While prokaryotic cells and eukaryotic cells have some things in common, there are more differences between them than similarities. Let’s explore below.
Prokaryotes are small, simple, single-celled organisms (unicellular) of the domains Bacteria and Archaea They range in size from 0.1-5.0 micrometers, and their most defining feature relative to eukaryotes is that they lack membrane-bound organelles, including a nucleus. It doesn’t mean that they don’t have anything going on in there though. Instead of being divided by membranes, prokaryotic cells are divided by specialized regions that are sorta-kinda like organelles (for all intents and purposes at least).
Instead of a nucleus, their DNA bundles together in a central region that we refer to as the Nucleoid. Speaking of DNA, theirs also has some defining features that set it apart from eukaryotes. As a refresh, eukaryotic DNA is double-stranded, linear, and found within the nucleus. Prokaryotic DNA is also double-stranded, but it’s circular and found within the cytoplasm instead. Some other features you might find in a prokaryotic cell include:
Cell Wall: provides structures and protection.
Cell Membrane: separates cells from outside environment.
Cytoskeleton: provides structure, protection, and plays a role in cell division.
Ribosomes: responsible for protein synthesis.
Capsule: a gelatinous layer surrounding the cell wall that helps the bacterium attach to surfaces.
Fimbriae: thin, hair-like structures that help with cellular attachment.
Pili: rod-shaped structures that also help with attachment as well as DNA transfer.
Flagella: a tail-like structure that helps with movement.
Some examples of prokaryotes include cyanobacteria (also called blue-green algae), Streptococcus bacterium (the bacteria that gives you strep throat) (boooo streptococcus 👎), and Escherichia coli bacterium (more commonly known as E. coli) (boo you too 😒).
Eukaryotes are organisms of the domains Protista, Fungi, Plantae, and Animalia and range in size from 10 micrometers to 100. Unlike prokaryotes, they do have membrane-bound organelles (including a nucleus). Eukaryotic cells are larger and more complex than prokaryotic cells. They’re typically multicellular, but there are a handful of examples of single-celled eukaryotes like phytoplankton, zooplankton, and protozoa.
Unlike prokaryotes, eukaryotic DNA is double-stranded, linear, and found within the membrane-bound Nucleus. It exists as entangled strands called Chromatin until a cell is ready to divide, at which point it’s packaged into tightly woven structures called Chromosomes.
Eukaryotes are typically divided into two categories: plants and animals (though they can also be protists and fungi). While they have many similarities, there are a few additional features found in plant cells that are not found in animal cells. We’ll go over those they have in common and those they don’t below.
Plants & Animals:
Nucleus: you haven’t forgotten already, have you? 🤨
Nucleolus: site of ribosomal RNA synthesis.
Plasma Membrane: separates cell from outside environment.
Cytoskeleton: provides structure, allows movement, and assists with cell division.
Mitochondria: powerhouse of the cell (need we say more? 🔋).
Ribosomes: site of protein synthesis.
Cytoplasm: a fluid-like substance between the nuclear envelope and plasma membrane.
Cytosol: a gel-like substance that is part of the cytoplasm and is the place in which organelles are suspended.
Endoplasmic Reticulum: site of protein folding and transport.
Vesicles/Vacuoles: membrane-bound sacs involved in storage and transport.
Golgi Apparatus: processes and packages proteins and lipids.
Chloroplasts: site of photosynthesis.
Central Vacuole: stores water and maintains turgor pressure (differentiated from animal cell vacuoles by its large size, central placement, and functions)
Cell Wall: surrounds cell membrane and provides structure and support.
Some examples of eukaryotes include flowers (plants), elephants (animals), mushrooms (fungi), and amoebas (protists).
Now that we’ve gone over the basics of prokaryotic and eukaryotic cells, the differences between them are a lot clearer. Let’s summarize below:
Eukaryotic cells have membrane-bound organelles, while prokaryotic cells have specialized regions.
In Eukaryotes, DNA is stored in the membrane-bound nucleus, while prokaryotic DNA is found in a central region within the cytoplasm called the nucleoid.
Eukaryotic DNA is linear and stored in the nucleus. Prokaryotic DNA is circular and stored within the nucleoid.
Prokaryotic cells are smaller than eukaryotic cells (0.1 to 5 micrometers compared to 10 to 100 micrometers).
Let’s not forget that as different as they are, prokaryotic cells and eukaryotic cells do have some common ground between them (maybe we’re not so different from algae after all ).
Both prokaryotic cells and eukaryotic cells have DNA (yes, yes, we know, we just talked about how it’s different–but the point is, they both have it).
Both prokaryotes and eukaryotes have a plasma membrane.
Both prokaryotic and eukaryotic cells have cytoplasm.
Both prokaryotic and eukaryotic cells have ribosomes.
Prokaryotes are small, simple, unicellular organisms of the domains Bacteria and Archaea that lack membrane-bound organelles. Instead, they have specialized regions that serve different purposes within the cell.
Prokaryotic DNA is found in the nucleoid, the central region of the cell.
Features of prokaryotic cells can include a cell wall, cytoplasm, cell membrane, ribosomes, capsule, fimbriae, pili, and flagella.
Examples of prokaryotes include cyanobacteria, Streptococcus bacterium, and Escherichia coli (among many others)
Eukaryotes are complex, typically multicellular organisms of the domains Protista, Fungi, Plantae, and Animalia. They have membrane-bound organelles that serve different purposes within the cell.
Eukaryotic DNA is stored within the nucleus either as chromatin or chromosomes.
Features of eukaryotic cells can include a nucleolus, plasma membrane, cytoskeleton, mitochondria, ribosomes, cytoplasm, cytosol, endoplasmic reticulum, vesicles/vacuoles, golgi apparatus, chloroplasts, central vacuole, and cell wall.
Examples of eukaryotes include flowers, elephants, mushrooms, and amoebas (among many others).
Eukaryotic cells differ from prokaryotic cells in size, by the presence of membrane-bound organelles, and the linear structure of their DNA which is stored within the nucleus.
Prokaryotic cells differ from eukaryotic cells in size, by their lack of membrane-bound organelles, and the circular structure of their DNA which is stored in the nucleoid.
Eukaryotic and prokaryotic cells are alike because of the presence of DNA, the plasma membrane, cytoplasm, and ribosomes.
1. Where is DNA stored in prokaryotic cells?
In the nucleoid, the central region of a prokaryotic cell.
2. Are human cells prokaryotic or eukaryotic?
The nucleus, which houses the DNA, or genetic material, cytoskeleton, organelles surrounded by cytoplasm, and nucleus enclosed by nuclear envelope are traits seen in human cells and hence makes our cells eukaryotic cells.
3. What are the primary differences between prokaryotic and eukaryotic cells?
The presence or absence of membrane-bound organelles and a nucleus, and the structure of their DNA.
4. What are the shared features between prokaryotic and eukaryotic cells?
Both prokaryotes and eukaryotes have DNA, a plasma membrane, cytoplasm, and ribosomes.
5. What is the difference between prokaryotic and eukaryotic DNA?
Prokaryotic DNA is double-stranded, circular, and found in the nucleoid while eukaryotic DNA is double-stranded, linear, and stored within the nucleus.
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