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C hapter 1Introduction to Biochemistry
Next time you’re at the gym, think about the fact that all the cells in your body
are working together to achieve your goals. Your muscles would rapidly fail without
your liver sending out the sugar they need to contract. You could only last for a
few minutes without your heart pumping oxygen-containing blood throughout your
body. And without your brain sending signals to mastermind it all, you wouldn’t even
make it out of the locker room.
One of the goals of this course is to understand how all the body’s organs work
together during exercise. This is pretty complicated, as you can imagine, so before
we can understand this cooperation between organs, we have to first discuss the
building blocks of the organs, cells. We can reduce cells even further down to their
components, the basic biological building blocks called lipids, carbohydrates,
proteins, and nucleic acids. That’s what biochemistry is all about, trying to
understand the whole from its parts.
Chemistry Review
If you were to take biochemistry, you would first have to take a semester of
introductory biology and four semesters of chemistry. However, our goal in this
course is to learn just enough about biochemistry to understand what’s going on at
the cellular level when we exercise. Let’s first highlight some of the most
important concepts from all those chemistry courses that you (probably) haven’t
taken so that you can follow the rest of this chapter.
A. What is chemistry anyway?
Chemistry is the study of material substances and the changes they undergo.
All materials are comprised of matter, which can be defined as anything that
occupies space and has mass. Matter is composed of extremely small particles
called atoms. There are about a hundred different kinds of atoms in nature. Each
, Exercise Physiology
J. T. Millard
Figure 1.
different variety of atom is called an element, and chemists arrange these in the
periodic table of the elements (Figure 1). Not all the elements are represented
equally, either on Earth itself or inside cells. All life forms are based on the
element carbon (C), and they also contain relatively large amounts of hydrogen (H),
nitrogen (N), oxygen (O), calcium (Ca), phosphorus (P), and sulfur (S).
Atoms are made up of even smaller particles: positively charged protons,
negatively charged electrons, and neutral neutrons. The arrangement of these
subatomic particles puts the protons and neutrons together in a massive nucleus
with the much smaller electrons buzzing around in a cloud. Atoms have equal
numbers of protons and electrons, which means that the charges cancel and they
are electrically neutral.
Atoms can link together in different ways to form molecules, with the “glue”
that holds them together called chemical bonds. Chemical bonds are often shared
pairs of electrons. The arrangement of atoms in a molecule is called the structure,
and chemists have developed some shorthand ways of representing structures.
As an example, let’s look at the molecule ethanol, which contains two atoms of
carbon, six atoms of hydrogen, and one atom of oxygen. We can write a chemical
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, Exercise Physiology
J. T. Millard
formula for ethanol as C2H6O, where the subscripts reveal how many of each type
of atom is in a molecule. Usually, chemists would draw this molecule using a simple
depiction with symbols for the atoms and lines for bonds (Figure 2C). This type of
drawing can be further simplified by leaving out the explicit bonds between carbon
and hydrogen, since there are so many carbon-hydrogen bonds in biological
molecules (Figure 2D).
B. Oxidation-Reduction Reactions Release Energy
Chemical reactions occur when the atoms in molecules link up in new ways to
produce new substances with different properties than the original materials,
often releasing or consuming energy. Energy produced during chemical reactions
can sometimes be harnessed to do useful work, such as lifting a big weight or
throwing a ball.
An important type of chemical reaction in metabolism is the oxidation-
reduction (or redox for short) reaction. Redox processes enable you to use the
energy within fuel molecules and also provide the energy needed to power your
Ipod and drive your car. Redox reactions involve the transfer of electrons from
one substance to another. The substance that loses electrons is oxidized, while the
substance that gains electrons is reduced. In reactions involving electron
transfer there cannot be an oxidation without a reduction. Note that when an
atom or molecule undergoes oxidation or reduction, it may end up with an unequal
number of protons and electrons, thereby becoming a charged species called an ion.
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