How would you explain the connection between glucose entering the body and energy created by the body to a friend, using your new biochemistry knowledge?

Glucose is a food source of energy for the body.  It is a simple sugar and once ingested, it enters the bloodstream through the digestive system and is distributed to the cells of the body.  These cells need to take in the glucose and access the energy of the molecule and use it to create the form of energy that is usable by the body- a molecule called ATP.  This molecule “traps” energy to be tapped in 3 high-energy bonds.  The “TP” stands for triphosphate:  Each phosphate bond contains a large amount of energy that can be accessed and utilized by the cell when broken and each ATP molecule contains three of these high energy bonds.

Here is a brief glimpse of the path that glucose takes in the creation of this energy housing molecule:  Once within a cell’s cytoplasm, a glucose molecule is broken down into two smaller molecules through a series of chemical reactions that yield 2 high energy ATP.  These reactions take place without molecular oxygen and, thus, are labeled as anaerobic.  This pathway, called glycolysis, is an important pathway for the body for two major reasons: First, it produces the form of molecule necessary to continue on with other energy producing pathways, and secondly, it can produce energy for the body when oxygen levels are low.  The molecules produced in glycolysis are now in a form that can enter into the mitochondria: the major site of energy production in the cell.  Within the mitochondria, the molecules enter the Citric Acid Cycle: a cyclic path of reactions that produces more ATP energy molecules as well as electron carriers.  Electron carriers are molecules that carry electrons transferred from intermediate molecules of the pathway to a final pathway called the electron transport chain.  This final pathway uses the shuffling of these electrons to the ultimate electron acceptor; oxygen; in a series of chemical reactions to pump protons across a membrane and harness the energy in many more high energy ATP bonds that can be utilized by the body. 

Important to note is that this journey that glucose takes through these energy-producing pathways is not a one-way street.  Many times the body calls for energy to be stored and this flow will stop and energy storage pathways will be utilized.  These are pathways that bind glucose molecules together and store them for times when there is a high-energy demand, like when you go for a run or engage in some other kind of exercise or hard work that calls for large amounts energy quickly.  Also important to remember is that ATP is used by the body to drive anabolic processes as well: the building up of molecules needed by the body.  Many of the chemical intermediates within the energy-producing pathways are also used in molecule building pathways.  In short, our body’s energy production, energy usage and energy storage pathways are complex and interwoven and quickly reactive to the immediate needs of the body as they change from one moment to the next.  Glucose gets pulled apart, put back together and transformed in many complex chemical reactions to meet the energy producing and energy storage demands of the body from one moment to the next.

What knowledge have you connected with past knowledge?

Ah, yes- your eyes are correct; your synapses are firing in the right directions; you are not mistaken:  You have read this question before- precisely two entries back!  Since this is a repeat question, I have chosen to approach my answer a bit differently this time:  I will begin my answer with a bit of an editorial angle before I label several specific connections that biochemistry has made for me with past studies.  However, before I do so, it is noteworthy to point out that this same question could be used for each week’s blog entry for this class, for biochemistry is full of connections to knowledge I have previously gained in past classes and explanations of "why and how".

On the Editorial Side: 

I simply love the Biochemical Connections boxes in our text:   As a student of medical and health sciences, these lovely little half-page snippets have become a lifeline for me, as they often connect complicated sequences of biochemical steps to the world I am working to enter into, through explanations of how these processes, or problems with the processes, cause various diseases or genetic differences.  Others explain the basic physiology of which I have previously studied in further detail and provide a thoughtful pause to make these connections of how chemistry basics are the fundamental basis behind what we are studying.  Taken together, each of these Biochemical Connections boxes is analogous to an island oasis in the midst of an ocean of protein abbreviations, nucleotide sequences and nucleophilic attacks!

Recent Connections:

In the most recent chapters of study, we have been immersed in the world of DNA.  Namely, the study of the biochemical processes of DNA replication, transcription and translation.  Thus, I felt it most appropriate to focus on a discussion of specific examples of connections I have made to past knowledge in these areas.

Connecting back to Microbiology:

In our recent study of DNA replication, we learned about the processes of proofreading and repair mechanisms in prokaryotic DNA.  In addition to errors made in replication to cause mutation, other mutagens can also have an effect on damaging DNA sequence and structure.  In this section I immediately connected back to my study of Microbiology when we learned about these various sources of mutagens, specifically UV light’s ability to cause thymine dimers; the formation of π electron bonds from the 5^th C and 6^th C of two adjacent thymine bases, which can alter the shape of the DNA molecule and cause errors in transcription and replication.  I understood this in my previous study, but only on a very high level.  Now, with my understanding of Organic Chemistry and Biochemistry, I can understand the nature of the bond that is formed and why this alteration in the three dimensional structure of the DNA molecule has such a drastic effect on the replication and transcription processes.  This connection also extends to the processes of repair mechanism and the need for recognition of the “correct strand”.  I distinctly remember learning in Microbiology about how prokaryotic DNA use methylation to flag the parent strand.  My understanding of this process stopped here at the time.  Now my understanding is much more complete, as I can connect back to Organic Chemistry and to Biochemistry and know that the adenine bases of the parent strands are methylated (meaning that -CH₃ is added) before replication, allowing enzymes to distinguish the parent strand (one without the mistake) from the newly synthesized stand (one with the mistake) and make the correction accordingly.

Connecting back to Anatomy & Physiology:

Another example I will give demonstrates connections between recently learned biochemistry concepts with those learned in Anatomy and Physiology.  This example involves the transcription factor cyclic-AMP-response-element-binding protein (CREB) which, in a neuron, activates genes associated with synapse-strengthening proteins that influence the development of long-term memories.  Reading about CREB and its role in the neuron provided a long overdue explanation for what those calcium ions were doing during depolarization when the calcium channels are opened:  They were activating enzyme pathways that ultimately activated CREB which activated the appropriate genes for the appropriate synapse-strengthening protiens!  I found this connection very interesting, as it provided a very specific example of the effect that transcription factors have on transcription and gene expression and connected with the broader level understanding of neurological function that I studied in Anatomy and Physiology.  In this sense (and, of course, many more examples that are like it) biochemistry has provided me with the explanation of "why and how" and the details that were missing in some of my prior studies.  This missing “why and how” have often times plagued me, as I have always thought it would be easier to understand the structure and function of the nervous system (and other biological systems) if I just had more detail to understand the underlying processes.