Reflecting back on the course, what are three major themes you would identify that connect the various topics discussed in this course – how are they connected to more than one topic, and how do they connect with what you knew before this course? What knowledge have you gained with regards to these three themes you have identified?

Various themes are present in Biochemistry that make it possible to see many connections with other biology and chemistry principles.  Biochemistry bridges these two disciplines in many ways; in explaining how principles of both disciplines govern the structure and function of organisms.  Reflecting back on the course and my studies, it has become apparent that the purpose of Biochemistry is to understand this bridge and how chemistry underlies and explains all biological processes (and how these individual chemical reactions might be targeted and altered to the advantage of the organism and to the disadvantage of disease).  Specific to this ”biochemical bridge”, three major themes have resounded through my  study of biochemistry and biochemical processes in the body:  chemical pathways and how they are interwoven, catalysis and control, and energy conversion.

Chemical Pathways & How they are Interwoven

An organism’s processes are comprised of chemical pathways that consist of many series of chemical reactions and steps that involve various molecules that lead to the creation of structures and functions vital to the organism.  These pathways are also intricately interwoven in a way that allows that organism to change quickly and efficiently respond to its internal and external environment.  Various pathways or steps in pathways can turn "on" or "off' other processes.  For example, DNA replication in eukaryotes is initiated by a complex of proteins that bind to replicators.  Some of these proteins; appropriately named replication licensing factors (RLFs); are cytosolic, meaning they are located outside of the nucleus, in the cytosol, and are separated from the DNA by the nuclear membrane.  During cell mitosis the nuclear membrane dissolves.  This makes it possible for the cytosolic RLFs to gain access to binding to the origin recognition complex and DNA and begin replication.  Thus, the pathway for replication in eukaryotes is intricately linked with and dependent on the pathways of cell mitosis.  Induction of one set of pathways makes the other possible.  We also see many examples of interwoven pathways when we study the many pathways of metabolism, as many of the intermediates created in the chemical reactions of the catabolic pathways, are also used in anabolic pathways to build the molecules of life.  In this sense, the direction and which pathways are activated are adjusted based on the immediate needs of the organism.  In conclusion, the ways in which these chemical pathways are linked together and affect one another are vital to the proper functioning of the organism.

Catalysis and Control

Another very important theme of this “biochemical bridge” is catalysis.  So many of the reactions in various pathways are nonspontaneous and even those ones that are spontaneous, if left uncatalyzed, would happen far too slowly to prove any use to an organism that needs to continually adjust to rapid changes and stimuli.  As we have seen in every reaction in glycolysis, the citric acid cycle, electron transport chain, β oxidation, etc., an enzyme or enzyme complex is involved in every step, catalyzing each chemical reaction and providing chemical control points that allow various pathways to be activated and inhibited, depending on the current needs of the organism.  Previous to studying biochemistry, I had encountered the topic of enzymes in relation to their role in digestion and how they function in catabolic processes.  Continuing with this theme, we have studied the enzymes involved in the breakdown of glucose to pyruvate.  On the flip side, we have also studied the enzymes that catalyze gluconeogenesis reactions- those anabolic reactions that respond to the energy needs of the organism being fulfilled, so that glucose can be resynthesized, stored and used later, when energy supplies are low.  We have also seen how these enzymes can be turned on or off (by other enzymes!) and, thus, function as control points for the pathways that they catalyze.   Enzymes are essential to life processes.

Energy Conversion

Lastly, the theme of energy conversion is ever present throughout all biochemistry principles.  This energy conversion is the main theme in our studies of the various metabolic cycles.  Energy is created from each of the cycles and used to drive anabolic metabolism.  Each and every biomolecule requires energy in its production, every process that we have previously studied in anatomy and physiology involves use of energy converted and then transferred within the body.  Even the very processes of energy conversion require energy already converted and created by the body.  To be specific, in the glycolytic cycle, 2 ATP molecules are required in the series of reactions that convert a glucose molecule to 2 pyruvate molecules, a process which produces 4 ATP molecules for an energy-yield of +2 ATP.  We need ATP to make ATP! and other biomolecules too.