Wednesday, December 31, 2008
To get started I thought I would address a few of Three Question Thursday questions(TQTQ from here on). I plan to use other TQTQ in future posts. So here goes.
TQTQ - 1: Why is there a change in ion concentration after ions flow inside the cell membrane?
Response: When ions such as Na+ move into a cell, for example through a membrane channel, they will move down their concentration gradient. This means that they move from where they are of higher concentration toward lower concentration (thanks to the second law of thermodynamics). This movement will continue until the concentrations become equal. This is to say that the number of Na+ ions per volume is now the same outside and inside the cell. The concentration of Na+ ions inside the cell has changed by the addition of Na+ ions from the exterior to the interior of the cell. Comments?
TQTQ - 2: What is the function of the alpha-helix portion of a trans membrane protein?
Response: Recall that proteins have primary, secondary, tertiary, and quarternary structures. See pages 71-76 of your text for a review. The alpha-helix is a secondary structure of proteins and help anchor the transmembrane protein in the membrane. Also recall that the cell membrane is a phospholipid bilayer with the hydrophillic (water-loving) portions pointing toward the cell exterior and interior and hydrophobic (water-fearing) portions arranged toward the middle of the membrane. This makes the middle of the membrane hydrophobic and because the alpha-helix is typically hydrophobic, it is this part of the membrane protein that is embedded within the membrane, anchoring the protein. See the image below. Comments?
TQTQ - 3: If alternative mechanisms of carbon fixation evolved in arid climates, what would happen to those mechanisms if those plants were to be moved from that climate?
Response: First, a point of clarification. Some CAM plants such as cacti are found in desert (arid) regions. Others such as pineapples (CAM) and corn (C4) live in regions that experience high daytime temperatures. Both climates expose the plants to excessive water loss through their stomates during the day. I know the book uses the term arid but I wanted to make clear that these alternative carbon fixation mechanisms are adaptations to high temperatures not just dry conditions.
Now to the answer. The answer to this question is not related to the content we are currently studying. Rather it is an evolutionary question. The simple answer is we do not know. Because mutation and genetic recombination are the source of new variation and both of these processes are of a random nature, we can not say this or that will happen. We can say that the selective pressures that resulted in these alternative carbon fixation mechanisms would be relaxed if we were to move the plant to a moderate climate such as the Puget lowlands. We could also form some hypotheses as to the direction of CAM plant evolution given a thorough understanding of CAM physiology. Left alone to nature this would take thousands of years if not longer. Alternatively, in a lab we might be able to accelerate CAM evolution but this would be artificial selection - like what we do with dogs, cats, and farm animals. I hope this helps. I love evolution questions, thanks Ana. Comments?
Feel free to comment on this post OR write your own question. I am back to monitoring the blog regularly.
Sunday, December 21, 2008
Before we begin I have a comment. The great quantity of information packed into each chapter of your text can be overwhelming, particularly if you attempt to memorize each fact disconnected from the others. Unless you have a mind that can hold on to thousands of isolated bits of information (there are people who can) you will become quickly frustrated. What will help you retain information is to connect all those facts to one or two big ideas. As you work to understand the big ideas incorporate the facts. If you do this it will cause your brain to link the many facts to the one or two, easier to recall, big ideas. Once linked in this way the facts become easier to recall and understanding of the big ideas is more complete. A word of warning, it still takes work. Trust your intelligence, have fun learning, and work.
Now to chapter 7.
Like all chapters of this text, chapter 7 presents a couple primary concepts and a few secondary concepts. The primary concepts are the compartmentalization of the cell and the cytoskeleton. The secondary concepts include; how cells are studied, comparison if prokaryotic and eukaryotic cells, power generation, and the nature of the cell surface. Two of the secondary concepts, power generation and the cell surface are covered in more detail in later chapters. In this post I will begin a discussion on the primary concepts.
Essentially, what a cell does is separate the inside from the outside. This allows the development of an interior environment different from the exterior. Once this difference is established the potential for unique chemical interactions in the cell exists. This concept can be extended to the interior of the cell.
If you look at the structure of the cell you can see that the interior is compartmentalized. In fact there are many compartments (organelles); a nucleus where DNA is kept, the closely associated endoplasmic reticulum, golgi apparatus, mitochondria, chloroplasts, and various membrane-bound vesicles. The big idea is that each compartment has a different internal environment which allows it to perform unique chemical reactions thus giving the organelle its function.
The primary example is the association between the nuclear membrane, endoplasmic reticulum, golgi apparatus, and vesicles. Take some time to learn how information leaves the nucleus, is processed in the endoplasmic reticulum, the product then shipped to the golgi apparatus and modified, and finally released as a vesicle. Note different kinds of vesicles are produced and have different functions and destinations.
So take a look at your book and familiarize yourself with the endomembrane system. If you have questions, be sure to post it here. Also, so far, four of you have accepted my invitation to the blog – thanks! But if you are in contact with the any of the others in the class tell them to join! So let me hear your questions and comments and get the conversation going. I will be blogging all break.
Friday, December 19, 2008
You may have noticed a change in the header. I have begun to invite former students who are now or are studying to be doctors and scientists. My hope is that they will join the conversation giving their perspective and broadening the knowledge base of the blog.
Also, you will see more gadgets (as Blogger calls them) appear in the left-hand margin. Feel free to suggest some. I will be placing links to science sites of interest.
Thursday, December 18, 2008
If you have questions during the holiday be sure to use the blog! I will be home all break and monitoring the blog. I will even add some comments on chapters through the break.
As this is a closed blog, I have given permission to only those AP Biology students who had email addresses listed on the school district database, Zangle. Any student who did not, was not invited. So let the others know about the blog and have them send their email address to firstname.lastname@example.org so I can include them. More later.
Wednesday, December 17, 2008
You probably know better than I how communication is changing. One of the fastest growing is Internet facilitated social networks. The blog is one way to create such a network and is the form I have chosen for all of us to communicate outside of the classroom. This blog will be used to post assignments, questions, and answers. Now, it is not necessary to submit a question only to me as through email. With a blog, when you post a question, all of you can contribute to the answer. With a blog you can save time because you can ask a question and receive an answer at any time of day. No need to wait until the next class period. As I learn all that a blog can do I will add more dimensions. So let's get blogging.