Eukaryotic organisms are quite diverse and include the single-celled yeast, the large elephant, and the gigantic, underground fungus that spans several hundred to several thousand acres of land. It is incredible that these rather diverse organisms are genetically similar enough to be grouped into the Domain Eukarya, which consists of the four kingdoms of Animalia, Fungi, Plantae, and Protista.
Eukaryotic and Prokaryotic Cells
One of the major classifications of all organisms is determined by the differences between eukaryotic and prokaryotic cells. Eukaryotic cells have a cell nucleus that contains organized, genetic material. Prokaryotic cells do not have a cell nucleus, but have genetic material that is clumped together and freely floating in the cytoplasm.
Eukaryotic Cell Structures
Eukaryotic cells are complex and consist of many membrane-bound organelles. The organelles to the cell are like the organs to the body. The University of Arizona Department of Biochemistry and Molecular Biophysics published the "Prokaryotes, Eukaryotes, & Viruses Tutorial" as part of The Biology Project in April 1997, which describes the different organelles that can be found in eukaryotic cells:
- The cell nucleus, the organelle that is the key difference between eukaryotes and prokaryotes, contains all of an organism's genetic material and a nucleolus within a double membrane called the nuclear envelope. The genetic material is deoxyribonucleic acid (DNA). The nucleolus produces ribonucleic acid (RNA).
- Mitochondria are the power plants of the cell. They are believed to have originated from bacteria and have their own DNA. This DNA is not unique because it is passed down from mother to offspring. Many people have the same mitochondrial DNA!
- The plasma membrane is a phospholipid bilayer that is part of the endomembrane system, which is a network of membranes that encloses all of the organelles of a cell. According to Biology, written by Robert J. Brooker, Erip P. Widmaier, Linda E. Graham, and Peter D. Stiling, and published by McGraw-Hill in 2008, the plasma membrane acts as a barrier between the inside and outside of the cell and contains the cytoplasm in which all of the internal organelles are suspended. Its membrane-bound proteins "allow the transport of substances into and out of cells." Other proteins act as receptors that determine how a cell interacts with its environment.
- Ribosomes make proteins that are either used within or transported out of the cell.
- The rough endoplasmic reticulum is so named because its surface is textured with ribosomes. The rough ER is responsible for sending various proteins to the appropriate organelles within the cell.
- The smooth endoplasmic reticulum serves several purposes. Like the rough ER, it is part of the cellular transport system. It also metabolizes lipids and detoxifies substances that are transported into the cell, such as harmful chemicals.
- The Golgi apparatus, or Golgi body, is the processing plant of the cell. According to Brooker et al., the Golgi apparatus "packages different types of materials into secretory vesicles" that are used to transport those materials out of the cell. It also processes proteins and lipids into different forms and transports them to the appropriate organelles within the cell.
- Lysosymes break down unusable materials that are transported into the cell as well organelles that are no longer of use.
- Peroxisomes, or microbodies, break down hydrogen peroxide, which is a byproduct of cell metabolism.
- Vacuoles are essentially storage units. They are more prominent in plant and fungal cells, but smaller vacuoles are used in animal cells.
- Plant and some other types of cells contain chloroplasts that allow the cells to use light energy to create sugars.
- Plants and fungi have cell walls that contain the plasma membrane and all of the other cell contents.
Eukaryotic Gene Expression
Eukaryotic gene expression is the process by which certain characteristics are exhibited. For example, a brown-haired human and blonde-haired person may produce a child with blonde hair, but that child will have the genetic information for both brown and blonde hair. Some genes are bundled together in the sense that they will always being expressed with certain other genes when activated.
Transcription in Eukaryotes
Gene transcription in eukaryotes occurs when genetic code in DNA is copied as an RNA molecule called messenger RNA (mRNA). The mRNA travels to the ribosomes that use the genetic information to produce proteins. Brooker et al. explain that "a gene is an organized unit of DNA sequences that enables a segment of DNA to be transcribed into RNA and ultimately results in the formation of a functional product."
All of the single organisms that we can see with the naked eye are eukaryotic organisms. Plants, animals, and fungi are all eukaryotic organisms. Some eukaryotic organisms can only be seen when they are part of colonies, such as collections of yeast. What they have in common is that they all contain genetic material that is neatly packaged within a special compartment in the cell called a nucleus. How that genetic material is used is incredibly diverse.
Diane Ursu - Diane Ursu joined Suite101 as a contributing writer in August 2009 and became a Feature Writer in January 2010. She is a freelance writer ...
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