Unit test scheduled for 2 November.
Cell Membranes Tutorial from the Biology Project
The last few units dealt with biology at the molecular level (and they won't be the last). Now we move up to the next level, that of the cell. In this unit we focus on the basic organization of cells, their internal structure, and some basic elements of cellular function. A following unit will explore the details of complex membranes that make up the outer boarder of cells and the structure of many of the internal cellular components. One of the challenges of this unit is the vocabulary; you need to learn and use a large number of new and sometimes strange sounding terms associated with the study of cells (i.e. cytology) and tissues (i.e. histology).
Learning Objectives: the successful student will be able to ...
- state the tenets of the Cell Theory as well as some of its exceptions.
- list several individuals who played a significant role in the development of the Cell Theory and briefly describe their contributions.
- explain why the "surface area to volume" problem limits the size of cells, perform simple calculations of surface area and volume of cells, and describe various strategies cells use to overcome this problem.
- name and describe the functions of the parts of a compound microscope and briefly describe other types of microscopes such as the transmission and scanning electron microscopes.
- distinguish between prokaryotic cells and eukaryotic cells and give examples and recognize examples of each.
- describe in some detail the structure of a "typical" prokaryote, name the two domains of prokaryotes, and give examples of beneficial, harmful, and extremophile prokaryotes
- name the important organelles of a eukaryotic cell, describe their structure, function, and their structural and functional relationship to other organelles.
- write a brief essay describing the "endosymbiotic" theory of eukaryote evolution and its supporting evidence.
- define and give examples of tissues, organs, and organ systems.
Lesson One: The Cell Theory.
Cells play such an import role in biology they have their own theory. This is not a theory that sprang up suddenly from the work of one or even a few scientists. It took years to emerge as a concept that brought together the contributions of many people working independently of one another. The Cell Theory is usually stated as three tenets:
- Cells are the basic, fundamental unit of life.
- All living organisms are composed of one or more cells.
- Living cells originate from other living cells.
Read the article from the Complete Microscope Guide which provides an excellent overview of the long development of the Cell Theory. As you read this article pay attention to the following points:
- The long time line it took for the Cell Theory to develop.
- The international effort this took; from the beginning Biology has been, like most sciences, a world wide effort.
- The role (and limitations) of technology in the development of the Cell Theory.
- The contributions of individual scientists; particularly those who made early contributions that led to the tenets of the Cell Theory listed above and those that helped develop the first effective microscopes.
Homework, Due 25 October. Pick one of the scientists mentioned in the article and write a brief biography. This must be in the format of a Power Point presentation that you will present to your classmates. Details to follow in class.
Lesson Two: The surface area to volume problem.
Most cells are small, quite small, and there is a reason for this; geometry. Cells must obtain nutrients, water, and oxygen from their environment. To do this they must move these materials across a membrane that forms the boarder between the cell's environment and its interior. It should make sense that the greater the surface area of the cell, the easier it is to do this. On the other hand, the larger the volume of a cell, the more nutrients the cell requires to maintain itself. Herein is the paradox; cells can increase their surface area to increase the efficiency of transporting nutrients across the cell membrane, but by doing so they also increase their volume and therefore their demand for even more nutrients. This is called the Surface Area to Volume problem. View the diagram in the Online Biology textbook to get an appreciation for the wide range of cells sizes. Read the accompanying material to review the SI units for these small dimensions (nano, micro, and millimeters). Read the following explanation of this problem and examples of solutions that cells use to cope.
Lesson Three: Prokaryotes, Eukaryotes and the three domains of life.
There are two types of cells, prokaryotic and eukaryotic. Although very different from one another in most respects, they also share much in common. You need to understand these differences and similarities and their implications for the evolution of cells. Read the following page by Lynn Fancher from the College of DuPage. Not only should you understand the differences and similarities between prokaryotes and eukaryotes, you should also appreciate the evidence that eukaryotic cells evolved from assemblages of symbiotic prokaryotes.
It turns out that not all prokaryotes are the same. Go to the tree of life at the University of California Museum of Paleontology and read their introduction to the classification of organisms into the three domains. On the diagram of the three domains, click on the Bacteria and then the Archaea. In both cases, then click on the Systematics link and explore the cyanobacteria and the various types of Archaea bacteria.
Homework, Due 29 October.
Read the article by Carl Zimmer on eukaryote evolution. Summarize this article using the posted guidelines. Be sure you use your own words to avoid plagiarism. Post your summary to the class blog. Instructions to follow in class. Once you have done that, you must also submit comments on the summaries of two of your classmates.
Image of sea anemone with symbiotic green algae in its cells from the Smithsonian National Zoological Park.
Lesson Four: Eukaryote cell structure and function.
This lesson will briefly survey the structure of a "typical" eukaryotic cell. Keep in mind that there is really no such thing as a typical cell. The diversity of cell types within and among species of eukaryote species is enormous. We will only touch upon the structures (or organelles) that make up a eukaryotic cell. As we progress through other units, we come back to these organelles and fill in the details. Your objective in this lesson is to learn the names, basic structure, location, and function of these organelles. In addition, you should appreciate the common features these organelles have in their construction and their functional interrelationships.
Start by going to Kimball's page on animal cells. Along with the diagram of a liver cell, there are links providing more detail on the various organelles labeled in this diagram. Begin with the "plasma membrane" more often called the cell membrane. The basic structure of this membrane is found not only in the cell membrane but in many organelles throughout the cell. For now understand the nature of the components of the membrane: phospholipids, cholesterol, and various types of proteins. Follow the link to the phospholipids to see how they are simple modifications of the triglycerides you studies earlier. Also understand how phospholipids are arranged in the membrane and their relationship to the proteins. Don't worry about the various types of proteins (for now).
Now, for reasons that will become clearer when you do your homework, follow the links to the various labeled organelles on Kimball's diagram in the following order.
- Nucleus: understand the arrangement of the membranes of the nuclear envelope and what "chromatin" is. Understand the primary function of the genes located on the chromosomes located in the nucleus.
- Rough and smooth endoplasmic reticulum and the ribosomes: Again, appreciate the membrane structure of these structures and their association with the ribosomes. Understand the different function of the smooth vs rough ER. Know the structural and functional relationship between these structures and the nucleus.
- Golgi Apparatus: Understand the membrane structure of this organelle, its structural similarities to the endoplasmic reticulum, and its function. Be able to describe how material manufactured on the endoplasmic reticulum is transported to the Golgi Apparatus and the role of the membranes in this process.
- Vacuoles, Peroxisomes, Lysosomes, and Pinocytotic vesicles: Appreciate the similarities in the structure of these organelles and the differences in their function. Where applicable understand their functional relationship to the Golgi Apparatus. Appreciate the role of these structures in the storage and transport of materials within the cell and across the cell membrane.
- Other organelles: For the remaining organelles, have a general understanding of their structure and function. For most of these, we spend a good deal of time with them in future units.
Homework, Due 31 October. Write a brief paragraph addressing the following questions and email your work to me using your Fontbonne Academy account.
- A number of textbooks have used the analogy of a factory to describe the functions and relationships among the cellular organelles you just studied with various cell structures playing roles similar to those that occur in the manufacture of complex products such as automobiles or buildings. Using the organelles listed above from nucleus to pinocytotic vesicles, describe their functions and their relationships to one another using this "factory" analogy.
- Using information from your readings describe two different situations where a medical condition is a consequence of the disruption of the normal functions of a cell organelle.
Lesson Five: Cell Memberanes, Structure and Function.
In the previous lessons we have been taking about the various organelles that sustain various function in eukaryotic cells. You learned that many of these organelles such as the nucleus, endoplasmic reticulum, Golgi apparatus, etc. are made of membranes with a common basic structure. In this lesson we will study that membrane structure in more detail. Go to the brief discription of membrane structure in Kimball. Take note of the double arrangement of the phospholipids that make up the bulk of the membrane (the phospholipid bilayer). In addition, notice the different types of proteins associated with the bilayer. These include integral, transmembrane, and peripheral proteins (these terms are not consistently used by various authors). Know the location of each of these types of proteins and the role of hydrophilic structures of these molecules. AP students note the role of the cytoskeleton in anchoring these proteins in the membrane. They don't rigidly fix the proteins but they do limit their movement. You can find a good animation here. The first few minutes of this Youtube video gives a nice view of membrane structures (the rest of the video is an excellent review of previous lessons). We will use the animations from this Carnegie Mellon University site to study some of the details of these membrane structures.
Homework, Due 14 November. Read the description of "G proteins" from Kimball. Understand how these important membrane proteins act as switches that, when coupled with membrane receptor proteins can regulate cell functions.You will probably find these videos helpful; here and here. Make a list of all the membrane associated proteins involved in the G protein signalling system and the specific function of each. Briefly describe two examples in this system where the change in protein shape is critical to protein function.
Lesson Six: The Fluid Mosaic Model.
All of the lipids and proteins that make up the membrane of eukaryotic cells are arragned in what is often called a "fluid mosaic" to reflect the fact that the phospholipids are moblie enough to be thought of as a liquid with various proteins floating in this matrix (diagram). The membrane associated proteins are often linked directly to other structures in the cytoplasm (diagram). This connect establishes lines of communication with the nucleus and other organelles. Other proteins function to transport material across the cell membrane. The transport can be either passive, requiring no outside source of energy, or the transport can be active, requiring a source of energy.