Where are we going with this? The information on this page should increase understanding related to this standard: Evaluate comparative models of various cell type…Evaluate eukaryotic and prokaryotic cells.
Article includes ideas, images, and content from Troy Smigielski (2021-09)
(Hmm… What now?)Okay… starting with cell theory, we are expected to agree that:
- All living organisms are made up of cells.
- Cells are the basic unit of life.
- All cells come from pre-existing cell.
Furthermore, all cells are made up from four basic biomolecules.
But all cells are not the same. There are two basic types of cells: eukaryotic and prokaryotic.
Eukaryotic Cells
The first type of cell we will discuss are called eukaryotic cells. To begin with, eukaryotic cells have a nucleus and membrane-bound organelles.
So, just what are membrane-bound organelles?
A membrane is an outer lining or covering.
Organelles are the smaller parts of the cell that have specific functions.
For example, the nucleus or the mitochondria are membrane-bound organelles. The organelles are the parts that make up a cell.
Secondly, eukaryotic cells have ribosomes, which are organelles that make proteins.
It is worth nothing here that plant cells have a cell wall whereas animal cells do not. So, eukaryotic cells occur both with and without cell walls.
Based on having eukaryotic cells, some organisms are classified as eukaryotes.
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| Source: Google |
If an organism has eukaryotic cells, it is said to be a eukaryote. Alternately, if an organism has prokaryotic cells, it is said to be a prokaryote.
Okay, cool…
Eukaryotes are generally multicellular although they can be unicellular. For instance, diatoms are unicellular eukaryotes that produce ~20% of earth’s oxygen.
Examples of eukaryotes include animals, plants, and fungi.
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| By File:Osmia rufa couple (aka).jpg: André KarwathFile:Boletus edulis (Tillegem).jpg: Hans HillewaertFile:Volvocales.png: Aurora M. NedelcuFile:Lightmatter chimp.jpg: Aaron LoganFile:Ranunculus asiaticus4LEST.jpg: Leif StridvallFile:Isotricha intestinalis.jpg: Agricultural Research ServiceCompilation: Vojtěch Dostál - File:Osmia rufa couple (aka).jpgFile:Boletus edulis (Tillegem).jpgFile:Volvocales.pngFile:Lightmatter chimp.jpgFile:Ranunculus asiaticus4LEST.jpgFile:Isotricha intestinalis.jpg, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=5321214 |
Some eukaryotic cells will have flagella and/or cilia. These function in cellular movement. The singular of flagella is flagellum.
In eukaryotes, DNA is housed in the nucleus in structures called chromosomes (chromatin).
Eukaryotic Cells Summary:
- Eukaryotic cells have a nucleus and membrane-bound organelles.
- Eukaryotic cells have ribosomes, which are organelles that make proteins.
- Eukaryotic cells are larger and more complex than prokaryotic cells.
- Based on having eukaryotic cells, some organisms are classified as eukaryotes.
- DNA is housed in the nucleus in structures called chromosomes (chromatin).
Prokaryotic Cells
The next type of cell we will discuss are called prokaryotic cells. Prokaryotic cells do NOT have a nucleus and do NOT have membrane-bound organelles.All prokaryotes have a cell wall.
Prokaryotic cells also have ribosomes.
Prokaryotic cells are smaller and less complex than eukaryotes.
Organisms made up of prokaryotic cells are called prokaryotes.
Prokaryotes are usually unicellular although there is some debate that they can be multicellular.
Examples of prokaryotes are bacteria and archaea.
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| https://www.google.com/search?q=prokaryotes |
Another difference between eukaryotes and prokaryotes is found in the way they arrange their DNA. Recall that in eukaryotes, DNA is housed in the nucleus in structures called chromosomes (chromatin). In prokaryotes, DNA is floating freely in one chromosome and is circular in shape.
There are extra pieces of DNA called plasmids that can be transferred to other prokaryotes. These typically carry favorable genes like antibiotic resistance.
Prokaryotic Cells Summary:
- All prokaryotes have a cell wall.
- Prokaryotic cells also have ribosomes.
- Prokaryotic cells are smaller and less complex than eukaryotes.
- Organisms made up of prokaryotic cells are called prokaryotes.
- Prokaryotes are usually unicellular, although there is some debate that they can be multicellular.
- DNA is floating freely in one chromosome and is circular in shape.
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The Endosymbiotic Theory
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| Source |
"The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship. Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell. Mitochondria and chloroplasts cannot grow outside their host cell." (Source, 2021-09-07)
According to the endosymbiotic theory one ancestral prokaryote (with no membrane bound organelles) ingested a mitochondrion.
Rather than the mitochondrion being broken down, the two cells began to live in symbiosis which is where they help each other out.
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| https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/15-the-origin-of-cells/endosymbiosis.html |
This process continued until the modern-day eukaryote evolved with many organelles.
So, according to the theory, the complex arrangement of the eukaryotic cells resulted from the happenstance merger of smaller prokaryotic cells that resulted in a symbiotic relationship. The repeated occurrence of these mergers eventually produced the various, specific-functioning cells we can identify now.
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Wow! That's a lot of stuff about something so small! Seriously… How about a chart?
Comparison of Eukaryotic and Prokaryotic Cells
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