Today, we’ll be moving on to the sixth universal feature of all cells that Alberts et al. describe for us:
All of this talk about DNA should be leading you to ask more and more questions, that you should hope to answer throughout your study of molecular cell biology. You might know that DNA is related to the concept of genes and genetics. But what is a gene anyway? A gene is defined as a segment of a DNA sequence, which corresponds to just one protein or set of alternative protein variants, or, to one catalytic, regulatory, or structural RNA molecule, per the 2014 text by Alberts et al.
How can we relate the concepts of DNA and genes? Undoubtedly, DNA molecules are large. Within DNA molecules are specifications for a number of proteins, often thousands. DNA contains special sequences, which can be likened to the punctuation we use when we write. Just like punctuation, the special sequences of DNA serve to define where information for each protein begins or ends. Different proteins are coded for when individual segments of the DNA sequence are transcribed into different messenger RNA molecules. One gene is represented by each DNA sequence of this particular type (Alberts et al. 2014).
However, somewhat of a problem is the fact that RNA molecules that are transcribed from the same DNA segment can often be processed in more ways than one. If this happens, a set of alternative versions of a protein may be created. This is more common in complex cells like those found in plants and animals. Another complication might arise when DNA segments are transcribed into RNA molecules that are not translated; rather, these RNA molecules serve different functions, including catalytic, regulatory, or structural ones. These segments of DNA also count as genes (Alberts et al. 2014).
Now that you know what a gene is, it is useful to know how the expression of genes within cells occurs. The entire process is regulated. Cells, as opposed to manufacturing a load of proteins all at once, all of the time, actually adjust their rates of transcription and translation of different genes. This occurs independently, according to need. Interspersed among the segments that code for protein are stretches of regulatory DNA. These regions are noncoding, and they bind to special protein molecules that control the rate of transcription locally. From one class of organisms to another, how much of the regulatory DNA exists and how the regulatory DNA is organized varies. However, like many other things that we’ve discussed, the basics of this process is universal for most organisms, with exceptions. So, the genome of the cell is responsible for directing when and where proteins are made within the cell, and also determine the nature of those proteins made. The genome of the cell is the sum total of the genetic information of the cell, personified in its entire DNA sequence (Alberts et al. 2014).
A prospective medical student, looking to help others succeed.