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     Chapter 13 is all about the Regulation of Genes (le duh). Gene regulation is vital in both prokaryotes and eukaryotes, but for different reasons. A focus of both prokaryotes and eukaryotes is conservation of energy. Eukaryotes the primary focus is cell differentiaon. All cells within a eukaryotic organism have the same genome, but the cells perform different functions and different structures. This is achieved through gene regulation, as cells have different proteomes and this differentin allows for the varied cell types that we see in eukaryotic organisms. One of the chief reasons for genetic regualtion in prokarotic organisms is the need to respond to environment and stay constantly agile and survive as long as possible. Without cells, or a singular celled organsim producing the right proteins for the right situation, the cell will struggle mightly. 

     The classic example for gene regulation in prokaryotes is the regulation of lactose breakdown in E. Coli. The breakdown of lactose is controlled by the lac operon, and this operon consists of three adjacent structural genes lacZ, lacY, and lacA. The chief regulating factors are the availablity of glucose and the availabilty of lactose. If lactose is not present, repressors bind to the promoter, inhibiting transcription. If lactose is present, these repressors are silenced and RNA polymerase can attach and transcription occurs of the enzymes needed to break down lactose, however the transcription is conditional upon the absence of glucose. When glucose is absent, levels of cyclic amp (cAMP) are high. cAMP is necessary to power Catabolite Activator Protein (CAP), and cap is neccesary for the transcription of mRNA and so on and so forth. So basically, a lac operon needs both low levels of glucose and high levels of lactose for the enzymes needed to break down lactose to be produced, which makes sense. 

     Gene regulation in eukaryotes is a lot more complicated. It is very rare to find such a straight forward example as the lac operon in a eukaryotic organism, as there are so many moving parts and different facets to protein production in eukaryotic organisms. A lot of eukaryotic gene control is related to the structure of the chromosomes, and this has to do with histones and what-not. Honestly, I don't know too much about eukaryotic gene control, I struggled comprehending a lot of the information because it was so complicated. I'm going to have to check out those virtual lectures. 

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