Download The Organic Macromolecules of Life

The Organic Macromolecules of Life
Carbohydrates
The night before a big event, many athletes “carb-load”, meaning they eat foods rich in
carbohydrates. Why? Many carbohydrates provide a usable energy source. Your body breaks down
carbohydrates and uses the energy in their chemical bonds to fuel the activities of life. Carbohydrates
are a group of chemicals that include sugars, starches, and cellulose. Carbohydrates provide energy for
organisms and they also provide structure for some organisms. For example, the cell walls of plants are
made of carbohydrates, which gives them their characteristic box shape.
Sugars, or saccharides, are relatively small, simple carbohydrates. Simple sugars are the
easiest chemicals for your body to break down. Have you ever had a sudden burst of energy after eating
something sweet? Sweet foods usually contain simple sugars that are easy for your body to break apart
quickly. When your body needs energy quickly, it breaks down simple sugars. Sugars commonly come in
two forms: monosaccharides (“single sugars) and disaccharides (“double sugars”), which are two
monosaccharides bonded together. When sugars are bonded together, a larger sugar and water are
formed. For example, glucose and fructose are two common monosaccharides. When glucose and
fructose are joined together, sucrose (a disaccharide) and water are formed. Notice that all of these
sugars end with the suffix –ose. The suffix –ose refers to sugar.
Many monosaccharides and disaccharides can be linked together into more complex
carbohydrates called polysaccharides (“many sugars”). Organisms form various complex carbohydrates
for energy storage. Most plants store energy in a polysaccharide called starch. When you eat a potato for
example, you are taking in the potato plant’s stored starch. Animals store energy in a polysaccharide
called glycogen, which is formed in the muscles and the liver. When athletes carb-load before an event,
they eat foods high in starches, which their bodies break down into simple sugars. Their livers and
muscles convert the simple sugars into stored glycogen. The glycogen can then be broken down into
simple sugars, which can be broken apart when energy is needed.
Simple sugars can also be joined together to make structural carbohydrates, such as cellulose.
You may not be familiar with the word cellulose, but cellulose is all around you – in desks, pencils, paper,
and any other plant material you see. In fact, cellulose is one of the most abundant molecules on Earth.
Lipids
Carbohydrates are used for some energy storage. When energy needs to be stored for an even
longer period of time, carbohydrates are converted into a different organic macromolecule – fat, which is
a type of lipid. Lipids are a group of organic molecules that includes fats, oils, waxes, phospholipids
and steroids. Generally speaking, waxes and fats are solids, whereas oils are liquids.
Fats, oils and waxes are the most common lipids. Fats and oils provide long-term energy storage.
Fats also act as insulation by helping to keep animals such as whales and penguins warm. Waxes
provide a different kind of protection; they repel water. Fruits and leaves produce waxes to keep water in
and thus prevent the plants from drying out. Ducks and other waterfowl produce waxes that makes their
feathers waterproof. Phospholipids are important structural chemicals in cells. These molecules form the
membranes, or outer protective covering, that surrounds cells. Phospholipids help control the substances
that enter and exit cells.The last group of lipids, steroids, serves as either structural molecules or
chemical messengers. Some steroids, such as cholesterol, are components of cell membranes and help
give the cell structure. Although cholesterol is essential to life functions, too much of it can be harmful to
your body. Other steroids serve as chemical messengers and carry messages from one part of the body
to another.
Many important lipids are formed from combinations of fatty acids and glycerol. Fatty acids are
long chains of hydrogen and carbon atoms that have a carboxyl group attached at one end. A carboxyl
group is a chemical group consisting of one carbon atom, one hydrogen atom, and two oxygen atoms.
Glycerol, which is an organic alcohol, contains three carbon atoms, each of which is connected to a
hydroxyl group. A hydroxyl group consists of one oxygen atom and one hydrogen atom. Many lipids are
formed from the attachment of two or three fatty acids to one glycerol. When fatty acids and glycerol are
joined together, a lipid and water are formed.
When people speak about nutrition and health, they often refer to saturated vs. unsaturated
fats. Lipids can be saturated or unsaturated molecules. Remember that fatty acids are made of several
carbon atoms connected together in a chain. If every carbon atom in a fatty acid is joined to another
carbon atom by just one, single bond, the fatty acid is saturated. If two bonds, called a double bond, join
a pair of carbon atoms the fatty acid is unsaturated. Saturated fats are commonly found in meats and
most dairy products. If a fatty acid contains several double bonds, it is said to be polyunsaturated.
Polyunsaturated fats tend to be liquid at room temperature and are used in many cooking oils, such as
sesame, peanut, and corn oil. Replacing saturated fats with unsaturated fats in your diet may help to
prevent heat disease.
Proteins
More than one half of the dry weight of your body is made of proteins. Proteins are large,
complex molecules composed of many smaller molecules called amino acids. Amino acids have an
amino group on one end, an R group, and a carboxyl group on the other end. An amino group consists
of one nitrogen atom and two hydrogen atoms. There are more than 20 amino acids found in living
things. All of the amino acids have similar chemical structures, but they differ in a region of the molecule
called the R group. The R group of each amino acid is unique to that particular amino acid.
When several amino acids are joined together, a protein and water are formed. The bond that
joins two amino acids together is called a peptide bond. A molecule of water is lost when a peptide bond
is formed between two amino acids. A dipeptide is two amino acids joined together. A polypeptide is a
long chain of several amino acids joined together. A complete protein contains one or more polypeptide
chains and may contain a few other chemical groups that are important to the protein’s proper function.
Proteins serve several functions in living organisms. They can be embedded in the cell
membrane and pump molecules into and out of the cell, they are responsible for the ability of cells to
move, and they make up hair, nails, and, muscles. Enzymes, a special category of proteins, help speed
up the rates of chemical reactions in living things. In fact, the functions of proteins are at the very center
of life itself.
Nucleic Acids
Killer bees are more aggressive when threatened than other types of bees. What makes these
bees behave differently? Some of their characteristics (and some of yours) are inherited. Molecules
called Nucleic acids control inherited characteristics. Nucleic acids are large, complex molecules that
contain hereditary, or genetic, information. They are composed of many smaller molecules called
nucleotides. Nucleotides are molecules that are built of three different parts: a special 5-carbon sugar, a
phosphate group that contains phosphorous, and a nitrogenous base that contains nitrogen. You will
learn more about these structures later in the year during the DNA unit. When nucleotides are joined
together, a nucleic acid and water are formed.
There are two kinds of nucleic acids – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA and RNA differ in their structures and functions. Similar to the blueprint for a builder, DNA carries
the instructions that control the activities of a cell. Similar to the builder, RNA uses those instructions to
build proteins. Therefore, both DNA and RNA are essential for life processes because they are involved
in the production of proteins, and proteins play a role in virtually every activity of every living organism.