Hassti & Amelia
Applications of Chemistry in…human metabolism!
Hassti’s Connections - #1 – 3 (energy and change, rate of chemical reactions, redox reactions)
Amelia’s connections - #4 – 6 (Acids/bases, Le Chatelier’s Principle, Entropy)
Metabolism refers to the set of chemical processes that happen in living organisms to maintain life. It is the sum of all anabolic
and catabolic processes in an organism. These processes allow organisms to grow, maintain their structures, and reproduce.
Metabolism is divided into two components: catabolism and anabolism. Catabolic reactions are processes that break
macromolecules into constituent individual subunits, while anabolic reactions are processes that produce large molecules from
smaller subunits. It seems as though human metabolism is solemnly concerned with biology. However upon greater research, it
is shown that this topic is in fact much related to chemistry. Here is a summary of six ways as to how human metabolism
relates to chemistry.
1.
Energy and Change
-human metabolism is a series of chemical reactions that involve energy change and transfer
-there are two main types of chemical reactions that are involved in human metabolism: endothermic and exothermic
reactions
-an exothermic reaction is a chemical reaction in which the energy of the products is less than the energy of the
reactants, in other words there is a net release of energy
-an endothermic reaction is a chemical reaction in which the energy of the products is more than the energy of the
reactants, in other words there is a net absorption of energy
-two main chemical reactions in metabolism that illustrate this are as follows:
Note: Only cellular respiration takes place in human metabolism. Photosynthesis occurs only in plants.
Cellular respiration: exothermic reaction -- ∆H < 0
C6H12O6 + 6O2  6CO2 + 6H2O
∆H = -2870 KJ/mol C6H12O6 used
Photosynthesis: endothermic reaction -- ∆H > 0
6CO2 + 6H2O  C6H12O6 + 6O2
∆H = +2870 KJ/mol C6H12O6 formed
According to the 1st law of thermodynamics, energy cannot be created nor destroyed; it can be changed from one form to
another or transferred from one object to another. Cellular respiration is the process that traps and stores the free energy from
the foods we eat. How is energy converted from one form to another in the body you may ask? Well the answer is ATP! ATP is
like a rechargeable battery. Energy is released when ATP (charged form) is converted into ADP (uncharged form). The energy
is then used to power endothermic reactions in the body. In other words, the energy is released to do work.
2.
Rate of Chemical Reactions
-the chemical reactions involved in metabolism occur under specific rates
-the human body has several mechanisms to increase the rate of the body’s chemical reactions ---one of which is the
usage of biological catalysts, aka. Enzymes—since the addition of heat would prove inefficient because the
temperature of the body must stay within a limit
-an enzyme is a biological catalyst (a substance that is used to increase the rate of a chemical reaction without being
consumed in the reaction)
-an enzyme increases the rate of chemical reactions involved in metabolism by lowering the activation energies that
are needed to trigger the reaction; therefore the number of reactants that have sufficient energy to react are increased
-an example of such an enzyme involved in human metabolism is lactase which is responsible for breaking down
lactose, a sugar found in milk
-lactase is found in the small intestines, liver and the kidneys and it catalyzes the breakdown of lactose to simple
sugars, glucose and galactose
Hassti & Amelia
-lactase lowers the activation energy by providing an alternative mechanism for the reaction because according to
Hess’s Law the enthalpy change of a physical or a chemical process depends only on the beginning conditions
(reactants) and the end conditions (products); it does not depend on the pathway or the reaction mechanism
3.
Redox Reactions
-reaction that involves the transfer of electrons
-oxidation is the reaction that involves the loss of electrons
-reduction is the reaction which involves the gaining of electrons
-a reaction that involves both oxidation and reduction is called an oxidation-reduction reaction, also known as a redox
reaction
-there are various redox reactions that occur in human metabolism
-the following are some examples:
-the electron transport chain
-reactions involving the reduction or oxidation of coenzymes such as
NAD+ and FAD
-for instance, the reduction of NAD+ to NADH involves the transfer of a
hydride ion which contains two electrons
NAD+ + 2 e- + 2 H+ <--> NADH + H+
-oxidative phosphorylation
Cellular respiration: exothermic reaction -- ∆H < 0
C6H12O6 + 6O2  6CO2 + 6H2O
∆H = -2870 KJ/mol C6H12O6 used
-this is an oxidation process because hydrogen atoms carry electrons away from carbon atoms in glucose to oxygen
atoms
-when the hydrogen atoms form covalent bonds with oxygen, the shared electron pairs occupy positions closer to the
oxygen nuclei than they did when they were part of the glucose molecule since oxygen is much more electronegative
than carbon
-example of a main redox reaction/process involved in metabolism: electron transport chain (ETC)
--composed of a series of membrane-associated protein complexes arranged in order of increasing electronegativity
--electrons are transferred to the first protein from coenzymes (NADH and FADH 2)
--electrons are then transferred between the proteins
--each component is reduced by gaining two electrons from the component before it in the chain and oxidized by
losing two electrons to the component after it in the chain
--the ultimate goal of this redox reaction is to create an electrochemical gradient (by pumping hydrogen ions across the
membrane) that is used to make more ATP (thereby harvesting energy)
Hassti & Amelia
4. Acids/bases, buffer systems in human metabolism
As we ingest foods, the process of digestion sets off a series of reactions in our body. Stomach acidity increases, but
that same acidity must be neutralized when the digested foods pass on to the small intestines. That becomes the jobs of
our bodies’ amazing buffer systems.
A buffer is any solution that contains a weak acid with its strong conjugate base, or a weak base with its strong
conjugate acid.
Stomach acid is neutralized by the sodium bicarbonate buffer system
HCl  H+ + ClNaHCO3  Na+ + HCO3HCO3- OH- + CO2
Na + OH + CO2 + H + Cl H2O + NaCl + CO2
HCl + NaCO3  H2O + CO2 + NaCl
5. Le Chatelier’s principle
Recall this reaction from earlier
CO2(aq) + H2O(l)  H2CO3(aq)  H+(aq) + HCO3-(aq)
As our body tissue release H+ into our blood, the reaction shifts towards the left, increasing [H2CO3] and [CO2], the
pressure from CO2 builds and we exhale, getting rid of the excess CO2 and restoring balance.
As our body tissue remove H+ from our blood, the reaction shifts towards the right, decreasing [H2CO3] and [CO2],
the pressure from CO2 drops and we inhale, restoring CO2.
6. Entropy
-As we touched upon earlier in the thermodynamics unit, all reactions increase entropy. Here we will take a look at …
-how even though as we age, we put random things into organized parts such as food into muscle; we are still
increasing the chaos level of the universe.
-How the change of breaking down food is larger than the order we create by using those broken down bits to repair
cells, build muscle etc.
-How through metabolism, we are ironically contributing towards our deaths via increased entropy of our body, but
still needing to do so.
Hassti & Amelia
References
-Hassti
Cellular metabolism . (n.d.). Retrieved from
http://www.biologyinmotion.com/atp/index.html
Christian, E. (n.d.). Chemistry of Metabolism . Encyclopedia of
diet . Retrieved from http://chestofbooks.com/health/nutrition/Diet Encyclopedia/Lesson -V I-Chemistry-Of-Metabolism.html
Cunningham, E. (1978). Biochemistry: mechanisms of metabolism .
South Carolina: McGraw -Hill Book Company.
Energy transfer in metabolism. (2002). Retrieved from
http://staff.jccc.edu/PDECELL/metabolism/ent rans.html
Gropper, S., Groff, J., & Smith, J. (2009). The Digestive System: Mechanisms for
Nourishing the Body. Advanced nutrition and human metabolism 5th ed (pp. 24-28). Wadsworth, US:
Cengage Learning.
The role of enzymes in metabolism . (n.d.). Retri eved from
http://www.titaneducation.com.au/samples/Biohsctr.pdf
Hassti & Amelia
References
-Amelia
Ben-Naim, A. (2007). Entropy demystified : the second law reduced to plain common
sense. Hackensack: World Scientific.
Chemical of the Week -- Biological Buffers. (n.d.).Science is Fun in the Lab of
Shakhashiri. Retrieved April 29, 2011, from
http://scifun.chem.wisc.edu/chemweek/biobuff/biobuffers.html
Gropper, S., Groff, J., & Smith, J. (2009). The Digestive System: Mechanisms for
Nourishing the Body. Advanced nutrition and human metabolism 5th ed (pp. 24-28). Wadsworth,
US: Cengage Learning.
pH Buffers in the Blood. (2008, September 5). Washington University Department of
Chemistry. Retrieved April 23, 2011, from http://www.chemistry.wustl.edu/