Examples of chemical reactions in daily life


You Are What You Eat!
Lipids and carbohydrates are
the scientific names for fats and
sugars. These natural substances
do a lot to keep us healthy. Along
with giving us energy, they help
cells move around the body and
communicate.
FATS
Eating healthy means that you need
to be careful about the amount of fat
in your diet. But a certain amount of
fat is really necessary: All humans
need lipids, called essential fatty
acids, from food because our bodies
can’t make them from scratch. Some
body fat is also necessary as insu-
lation to prevent heat loss and to
protect vital organs from the strain
of routine activities.
Lipids in adipose tissue (fat cells)
are a major form of energy storage
in animals and people. The “fat-
soluble” vitamins (A, D, E and K) are
essential nutrients stored in the liver
and in fatty tissues. Triglycerides,
another type of lipid, are especially
suited for stockpiling energy because
of their high caloric content. When
we need energy, our bodies use
enzymes called lipases to break
down stored triglycerides into smaller
pieces that participate directly
in metabolism.
The mitochondria in our cells
ultimately create energy from these
reactions by generating adenosine
triphosphate, or ATP, the main cur-
rency of metabolism.
In addition to providing and
storing energy, lipids do many other
things. They act as messengers,
helping proteins come together in
a lock-and-key fashion. They also
start chemical reactions that help
control growth, immune function,
reproduction and other aspects of
basic metabolism.
The plasma membrane is a perfect example of the rule that oil and water don’t mix.
Inside the Cell
Carbohydrate
Glycoprotein
Glycolipid
Cholesterol
Phospholipid
Protein
Outside the Cell
Plasma
membrane
Membranes are a hallmark of how organisms evolved

the ability to multitask.
The lipid molecule cholesterol
is a key part of the plasma mem-
brane, a coating that wraps around
every cell in the human body.
Although it does act as a protec-
tive barrier, the plasma membrane
is less like a rigid wall and more
like a pliable blanket. In addition to
lipids, the plasma membrane con-
tains sugars that stick out from its
surface and proteins that thread
through it.
It is an orderly arrangement
of ball-and-stick molecules called
glycolipids (lipid chains with sugars
attached) and phospholipids
(lipids marked with cellular tags
called phosphates).
When aligned “tail-to-tail,” these
fat-containing molecular assemblies
resemble a double array of match-
sticks lined up perfectly end-to-end.
The membrane forms more or
less automatically when the lipid
end of each glycolipid or phospho-
lipid matchstick is attracted to oily
substances: other lipids. The other
matchstick end, containing a sugar
or phosphate molecule, drifts natu-
rally toward the watery environment
typical of the areas inside or
between cells.
Membranes are a hallmark of
how organisms evolved the ability
to multitask. Membranes allow cells
to keep proteins and other mole-
cules in different compartments so
that more than one set of reactions
can occur at the same time.
In addition to the plasma mem-
branes around cells, organelles
inside cells are wrapped by similar,
lipid-containing membranes that
encase specialized contents.

Chemistry…For a Healthier
Enzyme Reaction
2 Hydrogens 1 Oxygen
H H
2H O2
H C H H C OH
H
H2O
H
Methane (Gas) Water Methanol (Liquid)
The enzyme methane monooxygenase converts methane into methanol, producing water
as a byproduct. Methanol is a liquid that can be transported much more easily than methane,
a gas that is hard to keep contained.
12 National Institute of General Medical Sciences
Chemists want to understand
how biology works so they can
manipulate it. Inventing environ-
mentally friendly approaches that
make reactions more efficient
and produce minimal toxic by-
products is an important goal of
modern chemistry.
Whether inside the body or in
the lab, all chemical reactions do
the same thing. They convert start-
ing materials, or reactants, into
products. Catalysts make these
reactions go faster.
A catalyst works by providing a
route for the reaction pathway to
make its product using less energy.
Catalysts are facilitators—they
are not used up in the reaction and
can be recycled. Researchers are
continually looking for catalysts
that are more efficient and friend-
lier to the environment. Such
catalysts are an important aspect
of “green chemistry.”
One recent advance in this area
is the development of “click chem-
istry,” which allows chemists to tailor
reactions very precisely. Thus, they
can generate substances quickly
and reliably. Click chemistry also
produces fewer byproducts—some
of which can be hazardous—and
less waste.
Harnessing biology’s magic
through chemistry underlies the field
of biotechnology—the use of biologi-
cal systems or living organisms to
make useful products and processes.
Biotechnology has applications in a
wide range of areas that benefit the
United States and the world.
Examples include genetically
engineered medicines and agricul-
tural processes that reduce farmers’
dependence on herbicides and
insecticides.
Other applications of biotechnol-
ogy include biodegradable plastics
and environmental cleanup tools.
For example, fatty acids are used as
detergents and as biofuels, which
are less damaging to the environ-
ment than many coal-based fuels.
Taking advantage of microbes’
innovative metabolism and defense
mechanisms can help us preserve
our environment, as well. This is the
case for methane, the main compo-
nent of natural gas that is used in
industrial chemical processes and is
second only to carbon dioxide as a
greenhouse gas that contributes to
global warming.
Methane is chemically inert, mean-
ing it does not break down easily. But
for some bacteria that live in extreme
environments like hot springs, chew-
ing up methane is a way of life (see
diagram, above). Understanding how
enzymes in these bacteria convert
methane into methanol and water
could possibly spur more efficient use
of the world’s supply of natural gas.
Some chemists study the role
of metal-containing molecules in
biological systems (see page 9). Many
processes in our bodies—like respira-
tion and reproduction—depend on
metals like iron, zinc and copper.
Iron, for instance, helps the protein
hemoglobin transport oxygen to
organs throughout the body. Many
metals act to stabilize the shapes
of enzymes.
Since metals are elements, the
building blocks of all chemical com-
pounds, they are already in their
simplest form and our bodies cannot
break them down.