Biology 101: Cells
Jumping Right In
There are many different kinds of cells. Some organisms consist entirely of one cell while others consist of billions. That is amazing! Just think of the kind of diversity. The amount of time and genetic mutations that have gone in to specializing each type of cell.
This article, for sake of simplicity, will focus only on prokaryotic and eukaryotic cells. Highlighting their similarities and differences. In the future, additional articles will come along to further demystify some of the more specialized eukaryotic cells.
Essentially, this article is meant to be a supplemental study aide to go along with what has been taught in class. In college I was lucky enough to have some amazing professors, but I also had the misfortune of having professors that didn't care if their students learned the material or not. I have been in the situation where I needed to learn for myself, and lets face it textbooks are boring. I learned organic chemistry because there were students that were given extra credit projections to make youtube videos about various topics of organic chemistry. My teacher just gave out worksheets and did not ever lecture or give guidance. These videos were vital to my education. It is my hope that this article can be used in a similar way.
Simply put, a prokaryote is a single celled organism that lacks membrane bound organelles, a mitochondria, or a membrane bound nucleus. So what are prokaryotes? Prokaryotes are divided into two domains: Archaea and Bacteria. It is thought that prokaryotes were the first form of life on Earth. According to the theory of evolution, all life on Earth derived from those first prokaryotes. The cellular structure of prokaryotic cells is much simpler than that of eukaryotic cells. The cell is inclosed inside of the cell wall, with only the flagellum and pili on the outside of the wall, used mainly for propulsion. Think of the cell wall like a coat, it protects the outside of the cell. Directly inside the cell wall is the cell membrane, this layer is responsible for regulating the flow of substances in and out of the cell. Inside of the cell membrane the organelles float freely in the cytoplasm. The ribosome, which is also found in eukaryotic cells, is responsible for the production of proteins. The nucleoid is where the DNA of the cell is stored.
Typically, prokaryotic cells reproduce asexually. This means that the offspring come from one individual and are identical to that parent. Of course, mutations can occur which is how things like resistance to antibiotics happen.
The Hardiness of Prokaryotic Cells
Prokaryotic cells are some of the toughest creatures on the planet. Think about it. They were the first forms of life that formed in the most extreme of conditions. They are able to survive at the bottom of the ocean, where there is no sunlight and it is just barely above freezing. They are able to leave inside the near boiling waters of the hydrothermal lakes of Yellowstone. There are even some bacteria that can survive off the hydrogen sulfide produced by volcanic activity.
Eukaryotic CellsClick thumbnail to view full-size
By definition a eukaryotic cell is any cell that has its genetic material bound within a nucleus. From that point there can be a broad range of differences. Some eukaryotic cells are single celled organisms while others are found inside of multi-celled organisms that can have many different types of specified eukaryotic cells. Think about it. Each cell in the human body (excluding all the bacteria in out gut and on our skin) is a eukaryotic cell. There are literally hundreds of different kinds of cells in the human body alone. That's some serious diversification!
Eukaryotic cells also contain other membrane bound organelles: such as the mitochondria, golgi apparatus, and chloroplasts. Each organelle is specialized to perform specific tasks within the cell.
Eukaryotic cells are able to reproduce by both asexual (mitosis) and sexual (meiosis) reproduction. This is one of the reasons why eukaryotic cells are able to have such a wide range of diversity, even within cell types.
A Side Note
As this article mainly focuses on the basics of each cell type it is not possible to devolve fully into the structure of the eukaryotic cell. I feel that doing so here would make this article too wordy and long. I intend to further my study aide articles and write one that focuses entirely on the eukaryotic cell and its organelles.
Similarities and Differences
One of the big similarities between the two types of cells is that they both contain ribosomes. However, the ribosomes in eukaryotic cells are larger than those found inside of prokaryotic cells.
Both prokaryotic and eukaryotic cells are capable of photosynthesis. However, one of the big differences is where the photosynthesis occurs in the cell. In the prokaryotic cell it takes place in the cell membrane, while in the eukaryotic cell it takes place in the chloroplasts.
Possibly, one of the biggest differences between the two cells is where the genetic material is stored. In eukaryotic cells DNA is stored within the nucleus, while in prokaryotic cells the DNA is not bound by a nuclear envelope and is freely within the cytoplasm.
Currently, there is debate on weather or not living bacteria has been found on Mars. If this is true and if the theory of evolution is correct, then one day it may be possible that eukaryotic cells may evolve from the prokaryotic bacteria on Mars. Maybe, as our exploration of our neighboring planet continues, we will get a front row seat in viewing the evolution of life on Mars.
The mitochondria and chloroplasts found in eukaryotic cells contain ribosomes. These ribosomes are smaller than the other ribosomes found inside of the cell and are more similar to those of the ribosomes found in prokaryotic cells. There are theories that suggest that both organelles were actually once bacteria. In theory primitive eukaryotic cells would have taken in the bacteria via phagocytosis and then the bacteria evolved in to the organelles that we know today.
For Further Reading
Interested in learning more about cells? Still have more questions? You can find more information at these websites:
Wikipedia - Prokaryotic Cells
Wikipedia- Eukaryotic Cells
For those of you with an iPhone or iPad you have access to iTunes U. If you have never checked it out before it is worth looking in to. Some professors at universities will publish their lectures on iTunes U. There are a lot of free podcasts, video lectures, and audio recordings on a wide range of topics. Best of all, its free.
The History Behind Cell Theory
This video is essentially a really shorted and simplified version of how our scientific understanding of cells changed throughout history and how the cell theory came to be.