In the first section of this page, you will write a daily summary of that day's class.  For example in  your chapter 2 blog, your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's lecture, outlining the major points.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.

A.  Daily Blog

9/29/2010 (submitted 9/29/2010)

You would think a cell membrane is just there to separate the cytoplasm from the extracellular matrix, but it is much more that that. The membrane of each cell is in a way its "resume", making it different from the others. Cell membranes are composed of a phospholipid bilayer (two layers). Each phospholipid contains a hydrophilic phosphate head, and two hydrophobic lipid tails. In the two layers, the hydrophobic tails face each other, while the hydrophilic heads are exposed to the water-based surroundings. This structure allows the membrane to be stable in the watery conditions. We first talked about the fluidity of the membrane with rising and dropping temperatures. As temperature drop, the membrane starts to solidify. To maintain normal fluidity, the lipids chains are unsaturated, shortened, and more cholesterol is incorporated between the phospholipids. Unsaturated lipids, contain a kind in one of the bonds, causing them to be unorganized and prevent solidification. When temperatures rise, the membrane becomes way to fluid, and could leak. Contrastingly, the lipids tail length is increased, and more lipids are saturated. Saturated lipids have no kinks, and organize better. The membrane it self serves complex purposes for the cell. The extracellular leaflet (the outside one) is the identity of the cell. The carbohydrates, the glycoproteins, and the cholesterol is found in this leaflet. These things identify the cell origin and the cell type. Now one may wonder how these things get here. The actual membrane is synthesized in the smooth ER (sER). Cotranslational modification brings the proteins to this membrane is the ER, and string the proteins through. The carbohydrate and glycoproteins are attached to the membrane in the sER lumen. From there the membrane is cleaved and forms a vesicle. It is further modified in the golgi apparatus. Then it is exocytosis-ed into the cellular membrane. Endocytosis of the membrane maintains the size of the membrane. The membrane also contains 3 types of proteins. Transmembrane, Peripheral membrane, and Lipid-anchored. Transmembrane proteins are arranged in a "inside out" structure. In normality, the tertiary structure of a protein exposes the hydrophilic polar ends to the surroundings. Since transmembrane proteins span the entire membrane, a section is exposed to the hydrophobic lipids tails. For the protein to be stable, now the hydrophobic ends a exposed to the outside. Peripheral membrane proteins attach to the transmembrane protein section in the cytoplasm. Lipid-anchored proteins attach to lipid tails, replacing the phosphate head. One again, proteins play an important part, so its not surprising to know that 25% of our genome codes proteins. 

Now imagine. If proteins end up in the wrong location, are in the wrong form, etc. What do you do? Well, you say hi to the new disease you just developed. If proteins do not end up where they belong and in the form they belong, the cell would have a wrong identity, it could let in harmful toxic substance, and disease the cell. 

10/1/2010 (submitted 10/5/2010) 

After talking about the structure of a membrane, we discussed how the membrane maintain a constant concentration gradient between the matrix and the inside of the cell. A cell at equilibrium is a dead cell, thus the cell has a constant negative charge along the inside of the membrane, with a positively charged cellular matrix. Movement of molecules in and out of cells is driven by a concentration gradient, thats why cells at equilibrium are useless and dead. With transport across the membranes, comes the need of energy. According to the law of thermodynamics, energy can never be destroyed or created, it just changes form; and entropy in always increasing, spontaneously. The greater the polarity of a molecule, the less the membrane is permeable to it. A greater concentration on one side than the other represents stored energy. 

Passive Transport does not require energy, because the molecules move down their concentration gradient. Molecules can either just diffuse across the membrane, or move through channels in a process called facilitated diffusion. Channel proteins are open on both ends, and molecules just flow through. Active transport, requires the use of ATP to move molecules against the concentration gradient. With a gradient, the cells also possesses potential energy. Ions follow a electromagnetic gradient. Primary active transport uses the hydrolysis of ATP to transport molecules. Secondary active transport uses a existing gradient to establish a another gradient. 

There are three types of proteins. Uniporters carry one type of molecule is one direction. Symporters carry 2 or mole different molecules in the same direction. Antiporters carry 1 or more types of molecules in, and 1 or more types out. ATP used in transports is not wasted, it is transfered into the gradient.

A great way Dr. Weber showed the form change of energy is by comparing a regular rubber band to a stretched rubber band. A regular rubber band, when released does nothing. But when energy is used to stretch it, that energy is now in the rubber band, and if the stretched rubber band is released, it will propel. All in all, a fun relaxing Friday lecture :)

10/6/2010 (submitted 10/6/2010)

Review day! For a test I'm extremely horrified about. Dr. Weber, feel empowered, we are scared of your test. Well for the first part of lecture, we quickly went over polarity of water and its properties. We also did a quick review about the role of cholesterol in membrane fluidity and how lipid lengths affect organization. Also looked at a little bit of the ER. Then we discussed a experiment testing the protein CHIP28 and its relation to aquaporins. CHIP 28 was added to a frog oocyte. Then that cell and an another were placed in a hypotonic solution. The cell contain CHIP 28 absorber water to the point of being lysed as compared to the control. This proved that CHIP28 indeed, provided a path way for water to diffuse through. Lecture ended with a round of question from the class regarding the test. 

B.  Useful Materials

1. Essential Biochemistry - This link gives a tutorial on membrane transport. it goes through how transport works in living cells, the types of transport, and why in general transport is important. Throughout, its          test knowledge of certain concepts. 

2. Introduction of Phospholipids to Cultured Cells with Cyclodextrin - Me(B)-CD greatly enhances translocation of membrane phospholipids from vesicles to cells in culture. The experiment studies the parameters which cause this to happens Conditions tested were incubation time, me(B)-CD concentration, vesicle concentration, cell type, and phospholipid structure. Also, cholestrol presence was also studies, since me(B)-CD is known to remove cholesterol, altering the membrane growth. In all, me(B)-CD mediates efficient transfer of long-chain (phospho) lipids from vesicles to cells without significantly compromising their growth or viability. 

3. The image below is th fluid mosaic model. It clearly shows the different types of membrane proteins, components of the extracellular matrix, and the structure of the bilayer. A great tool to understande membrane function.