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.
