Prokaryotes vs Eukaryotes
Prokaryotes vs Eukaryotes, what’s the difference and how do I remember which is which?
Prokaryotes are single-celled organisms that do not have a nucleus or any membrane-bound organelles.
Eukaryotes are single-celled or multi-celled organisms that do contain a nucleus and membrane-bound organelles.
A good way to remember the difference is to look at the Greek origins of the words.
Prokaryotes– pro means before, kary (derived from karyon) means nut or kernel (referring to the nucleus), and otes is just a plural suffix. So essentially prokaryotes means it has no nucleus.
Eukaryotes– eu means good or true, kary (derived from karyon) means nut or kernel (referring to the nucleus), and otes is just a plural suffix. So essentially eukaryotes means it does have a nucleus.
That’s the main difference, but there is much more to prokaryotes vs eukaryotes than that so let’s go a little bit more in depth.
Prokaryotes vs Eukaryotes Background Information
First, let’s start with cells. Cells are the basic units of life. In school, we learned about them as the “building blocks of life.” All living organisms are made up of cells (except for viruses), and a cell is also the smallest unit of life that can self-replicate on its own.
The human body is composed of trillions of cells. In fact, scientists have calculated that the human body consists of roughly 37.2 trillion cells. That’s a lot of cells!
Cells (and thus all living organisms) can be divided into two major types depending on their cell structure: prokaryotes and eukaryotes. In terms of age, prokaryotes have been around a lot longer than their counterparts. They were originally the only type of cell for billions of years (the oldest records date them back to roughly 3.5 billion years ago), and eukaryotes evolved from them roughly 2-3 billion years ago.
A major distinguishing difference between prokaryotes and eukaryotes are organelles.
Organelles are tiny membrane-bound structures or compartments that perform specific functions in a cell. Examples of organelles would be a nucleus, chloroplasts, or mitochondria.
Prokaryotes do not contain organelles, and eukaryotes do contain organelles.
The reason organelles play such an important role for cells is due to size. The larger the cell size means that more cell processes are going on. Therefore, they need more space.
So larger cells contain more DNA which means more transcription is happening. More transcription means more translation, and more translation leads to more proteins being synthesized. Since so much is going on and the cells are so much larger organelles then become crucial in organizing cellular functions.
Prokaryotic cells are much smaller than eukaryotic cells, so they do not need organelles because they do not have as many components. They also do not have as many cellular functions going on and are much simpler. Their smaller size and simpler structure allow them to reproduce rapidly and effectively.
In comparison, eukaryotic cells are much larger, more complex and have more components.
To classify cells even further we can think back to high school and remember our classification system. All organisms fall into three domains (the highest taxonomic rank): Archaea, Bacteria, and Eukarya.
Both Archaea and Bacteria are prokaryotes, and Eukarya are eukaryotes as the name suggests.
Humans, animals, and plants are all eukaryotes, and they have more complex cellular structures and functions.
Prokaryotes vs Eukaryotes Structural Comparisons
Structurally eukaryotes are larger and more complex, and therefore they have more structural components than prokaryotes do.
Prokaryotes are single-celled organisms, so they have fewer components. While they do not have a nucleus or any membrane-bound organelles, they do have other components. They have a nucleoid, a cell wall, a cell membrane, cytoplasm, a cytoskeleton, chromosomes, flagella and pili, vesicles, and plasmids.
Eukaryotes can be single-celled or multi-celled organisms (they are usually multi-celled), so they have a lot more components. While they do contain a nucleus and membrane-bound organelles they also have other components as well. They have a nucleus, a cell wall, a cell membrane, cytoplasm, a cytoskeleton, chromosomes, flagella, mitochondria, an endoplasmic reticulum, a Golgi apparatus, lysosomes, peroxisomes, vesicles, and plasmids.
Prokaryote vs Eukaryote Structural Differences
Here are the main structural differences between prokaryotes and eukaryotes.
Since having a nucleus or not is one of the defining differences between the two let’s look at that first.
In prokaryotes, there is no nucleus, but there is a nucleoid. This is the region where their DNA is stored, but it is not an actual membrane-bound organelle or even a structure.
Eukaryotes have a nucleus which is an actual membrane-bound organelle that contains their DNA.
Prokaryotes do not have an endoplasmic reticulum, a Golgi apparatus, lysosomes, or peroxisomes; but eukaryotes do.
The endoplasmic reticulum is a network of interconnected membranes that help with synthesis in a cell.
The Golgi apparatus is a “folded” set of membranes that processes proteins and is involved in intracellular transportation.
Lysosomes are organelles that help a cell to break down materials, proteins, and membranes.
Peroxisomes are organelles that contain enzymes that primarily oxidize amino acids and fatty acids.
Prokaryote vs Eukaryote Structural Similarities
Here are some of the structural similarities between prokaryotes and eukaryotes, but even here there are some small differences, and some structures are more common in one or the other.
While both prokaryotes and eukaryotes have a cell wall, it is more common in prokaryotes than in eukaryotes. Also, the cell wall in prokaryotes is more complex than that of eukaryotes. The cell wall is the rigid layer that lays right outside the cell membrane and helps give a cell it’s defining shape.
Both prokaryotes and eukaryotes have cell membranes which surround the cytoplasm of the cell and protect the cell’s inner components. Cell membranes are semi-permeable. However, in prokaryotes, the cell membrane rarely contains steroids (such as cholesterol or sex hormones), but most eukaryotes do contain them.
Both prokaryotes and eukaryotes have cytoplasm which is a clear, thick fluid that contains all a cell’s organelles.
They also both have chromosomes which are DNA molecules that have all or part of an organism’s genetic makeup. Prokaryotes typically have one chromosome (there is a bacterium that has two chromosomes), and eukaryotes always have more than one.
Flagella and pili
Prokaryotes have flagella and pili that help them with their motility. Flagella are taller and have more of a “tail” shape while pili are shorter and have more of a “hair” shape.
Some eukaryotes do have flagella (for example sperm), but they do not have pili. The flagella in prokaryotes are made up of proteins, while in eukaryotes it is made up of microtubules.
Both prokaryotes and eukaryotes have a cytoskeleton which gives them their shape and is made up of microfilaments and microtubules. In prokaryotes, the cytoskeleton is not always present, but in eukaryotes, it is always present.
Both prokaryotes and eukaryotes have vesicles. Vesicles are small fluid-filled sacs that help transport cellular material from one area to another in the cell.
Both prokaryotes and eukaryotes also have plasmids which are small DNA molecules that replicate. They are much more common in prokaryotes (especially bacteria) than in eukaryotes.
Prokaryotes vs Eukaryotes Genetic Comparisons
Now that we understand their structure let’s look a little bit closer at their genetics.
Prokaryotes vs Eukaryotes DNA
First, let’s look at their DNA. The main difference between their DNA is that prokaryotes have small, circular DNA genomes, and eukaryotes have larger, linear DNA genomes.
Because prokaryotic DNA can interact with cytoplasm, this allows transcription and translation to occur at the same time and in the same location (in the cytoplasm).
Transcription is where DNA is turned into RNA, and translation is the synthesis of proteins.
However, in eukaryotic DNA transcription and translation happen at different times and in different locations. Transcription happens in the nucleus, and translation happens in the cytoplasm.
Prokaryotes vs Eukaryotes Chromosomes
Next, let’s look at their chromosomal differences. Prokaryotes have one chromosome which consists of one double-stranded circular DNA. This chromosome is stored in the nucleoid region.
Because they only have one chromosome, they are not considered to have “true” chromosomes. This is because they typically store most of their DNA on plasmids instead. Eukaryotes have many chromosomes, and occasionally they also have plasmids as well.
Prokaryotes vs Eukaryotes Haploid / Diploid
Another notable difference is that most prokaryotes only have one copy of each gene (meaning that they are haploid). While most eukaryotes have two copies of each gene (meaning that they are diploid).
Prokaryotes vs Eukaryotes Sexual Reproduction Comparison
There are also differences in how prokaryotes and eukaryotes reproduce.
Prokaryotes reproduce asexually meaning that a single organism can produce offspring on its own, and the offspring only inherits genes from that one organism.
Prokaryotes usually asexually reproduce using a process called binary fission. This is where a single entity breaks in half into two identical parts. The two identical parts (also known as daughter cells) have the same genetic makeup as their parent cells.
Eukaryotes can also reproduce asexually, but generally reproduce sexually meaning that two organisms reproduce to produce offspring, and the offspring receives half of its DNA from each of its parents.
When eukaryotes reproduce asexually, they use a process called mitosis. Mitosis is when a single cell divides into two daughter cells. These daughter cells have the same number and type of chromosomes as their parents.
When eukaryotes reproduce sexually, they use a process called meiosis. Meiosis is when a single cell divides twice to produce four daughter cells. These four cells contain only half of the genetic material from the parent cell. These are sexual cells which are sperm (for males) and eggs/ovum (for females).
Prokaryotes vs Eukaryotes Summary
While initially, it can be confusing to remember the difference between prokaryotes vs eukaryotes, one of the main ways to remember is to look at the words themselves.
Pro (before) and kary (nucleus) refer to not having a nucleus.
Eu (true) and kary (nucleus) refer to having a nucleus.
That is the key defining characteristic: that prokaryotes have no nucleus and eukaryotes do have a nucleus.
Prokaryotes also do not have membrane-bound organelles and reproduce asexually. Eukaryotes do have membrane-bound organelles, and they typically reproduce sexually.
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