Continuing with the study of cell biology, is the eighth universal feature of all cells, according to Alberts et al.:
The point here is very straightforward. Plasma membranes surround all cells, and serve as selective barriers allowing a cell to concentrate the nutrients that is has gathered from its environment, retain the products synthesized by the cell for its own use, and also allows the cell to excrete waste products. All in all, plasma membranes maintain the integrity of the cell as a chemical system that is coordinated (Alberts et al. 2014).
It is important to know also what makes up a plasma membrane. Particular molecules arrange themselves in a particular way to make a plasma membrane, and understanding their arrangement can tell you more about the properties of a plasma membrane. Firstly, the molecules making up a plasma membrane are amphiphilic, which means that they consist of two parts, with one of them being hydrophobic or water-insoluble, and the other being hydrophilic, or water-soluble. When placed in water, the molecules take up a position with hydrophobic portions making contact with one another, allowing them to hide from the water. Predictably, then, the hydrophilic portions of the molecules are exposed and are not “afraid” of the water. Molecules that are amphiphilic, such as those in this specific case, aggregate in a particular way in water, causing the creation of a bilayer, which then forms small closed vesicles. The molecules that are a part of the process described above are phospholipid molecules (Alberts et al. 2014). Below, you can see what a phospholipid bilayer as described looks like.
It should be noted that without regards to slight variation in chemical details, hydrophobic tails of the predominant membrane molecules in all cells are hydrocarbon polymers. The process described above is evidence of an important principle of cells, which is that molecules produced by a cell self-assemble in order to achieve structures that the cell requires (Alberts et al. 2014).
Going back to the original point, plasma membranes allow materials to be imported into the cell and exported out of the cell in accordance with the cell’s needs. This means that the cell is permeable to some degree. Cells, for this reason, have specialized proteins embedded in their membrane, known as membrane transport proteins. These proteins are by and large the major determinants of the molecules that are permitted to enter the cell. Catalytic proteins inside of the cell thus are tasked with determining the reactions that the particular molecules undergo. Thus, it can be said that when a cell manufactures specific proteins, genetic information is recorded in the DNA sequence, and this then dictates the entirety of the chemistry that occurs within the cell. More than just the chemistry, the form and behavior of the cell is also dictated in this way (Alberts et al. 2014).
So, since it’s been quite a while since we’ve done a post on cell biology, I thought that I would pick up where I left off last time, today. In my last post that was made over a month ago on the subject, I was going over the universal features of all cells, per Alberts et al. The seventh in this series is the following:
The point that Alberts et al. make here is fairly straightforward. All cells make DNA, RNA, and protein. Thus, they all using similar small molecules in similar processes. Small molecules including simple sugars, nucleotides, amino acids, and other universally-required substances. As an example, ATP is needed for DNA and RNA synthesis, and is also a carrier of the free energy that is required to drive many different chemical reactions that occur in the cell (Alberts et al. 2014).
It is important to note, finally, that small-molecule transfers of different cells may share similar properties in a broad aspect, but have many details that are inherently different. As an example of this, plans are a type of organism that requires very simple nutrients. Plants utilize energy from sunlight to be able to make their own small, organic molecules. It is a bit more complicated for animals, who feed on living things and in many cases are required to obtain many of their organic molecules in a ready-made form. This is a point to which we will likely return in later studies of the subject, in more detail (Alberts et al. 2014).
In the last post, we discussed monatomic and polyatomic ions. In this post, we will go over binary molecular compounds, which is a fairly simple topic of study, with a few rules to follow. A binary compound, as the name implies, is a compound that is composed of two elements. Binary compounds can be separated into two groups, according to Ebbing and Gammon in their 2009 textbook.
When writing the formula for a compound, there are also conventions to follow, dictating the order in which the elements are placed. The order that elements in the formula must follow is as given below, by Ebbing and Gammon:
Element: B Si C Sb As P N H Te Se S I Br Cl O F
You might notice, from this, that these elements actually follow somewhat of a pattern of increasing group number, with B from Group IIIA, Si and C from Group IVA, elements Sb to N in Group VA, H not included, elements Te to S in Group VIA, elements I to Cl in Group VIIA, O not included, and F not included (Ebbing and Gammon 2009).
If you noticed this trend, what this tells you is that you can find out the order that elements in a binary compound should be written in, easily, using a periodic table of elements, which you will almost always have available to you when studying chemistry or taking an exam in the course. Specifically, this order goes from decreasing to increasing nonmetallic character. So, the elements in the beginning are more metallic than those further down the line (Ebbing and Gammon 2009).
Now, on to the rules for naming binary molecular compounds. Yes, more rules, also given to us by Ebbing and Gammon:
There are some things to consider, however. There are random oddities of the naming system that you should be well aware of, per Ebbing and Gammon:
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