Chemical bond formation
What is chemical energy?
Chemical bonds form spontaneously between complementary atoms meeting in the correct orientation. High energy, fast moving atoms are more likely to collide. Complementary atoms are those whose outer electron shells are more stable when the atoms share electrons.
Physics defines energy as an ability to do work. Chemistry simply maintains that molecules possess energy due to their motion. Physiology is a specialized form of chemistry, so it is easiest to stick with the definition from chemistry. It is atomic motion, defined as kinetic energy, which humans and other life forms organize into special functions called physiology. Atoms have moving parts and they themselves are in motion.
Bond energy
Bond energy is defined by how much the participating atoms are limited in their motion by the bond. Plants produce high energy sugar molecules by capturing the sun’s radiant energy to rearrange carbon dioxide and water. When sugar is metabolized back to carbon dioxide and water the sun’s energy becomes available to power physiologic functions. That molecules possess a predictable amount of motion (kinetic energy) at any given temperature is based on scientific observation.
The inherent property of molecules to move is not emphasized in physiology textbooks. Rather molecules are drawn in one of several static formats. While such illustrations are useful, they are also misleading. Motion (kinetic energy) at the molecular level in humans is not noticeable. It is difficult to imagine, because our bodies appear to be relatively solid objects. The thought of all that random motion under the surface is a bit alien.
This video by graduate student Jamie Schiffer at the University of California San Diego provides a peak at the latest ways in which molecular motion of large molecules is predicted.
High energy bond
Students in anatomy and physiology hear a lot about high energy bonds being made during sugar metabolism. Chemical bond formation between atoms to make molecules is a matter of the right partners with enough kinetic energy coming together in the correct orientation in space. The more kinetic energy an atom has, the faster it moves and the more likely it will meet a possible partner in the correct orientation.
Within molecules there are both high energy and low energy bonds. The low energy description comes from the fact that bound atoms have lower kinetic energy, or freedom of motion, than before the bond was formed. That is atoms linked together move more slowly than they did as separate entities. The energy that they lose is then available to other molecules nearby that are in the correct orientation.
The phrase strong bond is used interchangeably with the description ‘low energy bond’. In contrast, a ‘high energy bond’ is one where the participant atoms retain a lot of the kinetic energy they had before the bond was formed. The retained kinetic energy of atoms in such bonds weakens the bond. Therefore, the phrase weak bond is used interchangeably with the description ‘high energy bond’.
Energy transfer
Enzymes are large protein molecules that collect and place smaller molecules in the correct orientation so that chemical bonds and their energy content can be transferred between them. Key to understanding how energy is extracted from sugar rests with the fact that the molecular bonds in sugar are much weaker than the final bonds in the products of sugar metabolism, carbon dioxide and water. It takes less energy for the body to break the bonds in sugar than is released to the local environment of the enzyme surfaces by the formation of carbon dioxide and water in the final step.
Further reading
Water’s Chemistry Governs Physiology
Physiology: Custom-Designed Chemistry
Do you have questions?
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Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts is now Manager at Reece Biomedical Consulting LLC.
She taught physiology for over 30 years to undergraduate and graduate students, at two- and four-year colleges, in the classroom and in the research laboratory. Her books “Physiology: Custom-Designed Chemistry”, “Inside the Closed World of the Brain”, and her online course “30-Day Challenge: Craft Your Plan for Learning Physiology”, and “Busy Student’s Anatomy & Physiology Study Journal” are created for those planning a career in healthcare. More about her books is available at https://www.amazon.com/author/margaretreece. You may contact Dr. Reece at DrReece@MedicalScienceNavigator.com, or on LinkedIn.
Dr. Reece offers a free 30 minute “how-to-get-started” phone conference to students struggling with human anatomy and physiology. Schedule an appointment by email at DrReece@MedicalScienceNavigator.com.