CARBOHYDRATES:
Sweet, Sweet Carbs
Carbohydrate is a fancy way of saying "sugar." Scientists came up
with the name because the molecule have many carbon (C) atoms
bonded to hydroxide (OH-) groups. Carbohydrates can be very
small or very large molecules, but they are still considered sugars.
Plants can create long chains of these molecules for food storage
or structural reasons.
What's It Used For?
A carbohydrate is called an organic compound, because it is made
up of a long chain of carbon atoms. Sugars provide living things
with energy and act as substances used for structure. When
sugars are broken down in the mitochondria, they can power cell
machinery to create the energy-rich compound called ATP (adenosine triphosphate). Some examples
of structural uses might be the shell of a crab (chitin) or the stem of a plant (cellulose). We'll talk about
them in a little bit.
Saccharides
Scientists also use the word saccharide to describe sugars. If there is only one sugar molecule, it is
called a monosaccharide. If there are two, it is a disaccharide. If there are three, it is a trisaccharide.
You get the idea.
Simple Sugars
What about the simplest of sugars? A sugar called glucose is the most important
monosaccharide on Earth. Glucose (C6H12O6) is created by photosynthesis and
used in cellular respiration. When you think of table sugar, like the kind in candy, it is
actually a disaccharide. The sugar on your dinner table is made of glucose and
another monosaccharide called fructose (C6H12O6). These sugars have the same
numbers of atoms, but they are different structures called isomers.
Polysaccharides
When several carbohydrates combine, it is called a polysaccharide ("poly" means many). Hundreds
of sugars can be combined in a branched chain. These chains are
also known as starches. You can find starches in foods such as
pasta and potatoes. They are very good sources of energy for your
body.
Sugars for Structure and Support
An important structural polysaccharide is cellulose. Cellulose is
found in plants. It is one of those carbohydrates used to support or
protect an organism. Cellulose is in wood and the cell walls of
plants. You know that shirt you're wearing? If it is made of cotton, that's cellulose, too! There can be
thousands of glucose subunits in one large molecule of cellulose. If we were like some herbivores or
insects, such as termites, we could eat cellulose for food. Those animals don't actually digest the
polysaccharides. They have small microorganisms in their bellies that break down the molecules and
release smaller sugars.
Polysaccharides are also used in the shells (chitin) of crustaceans, such as crabs and lobsters.
Chitin is similar in some ways to the structure of cellulose, but has a far different use. The shells are
solid, protective structures that need to be molted (left behind) when the crustacean begins to grow. It
is very inflexible. On the other hand, it is very resistant to damage. While a plant may burn, it takes
very high temperatures to hurt the shell of a crab. If you know the way crabs are cooked, you know
that the crab meat cooks on the inside of the shells when it is boiled. There is no damage to the shells
at the temperature of boiling water (H2O at 100oC).
LIPIDS:
Lipids are another type of organic molecule. Remember that organic means they contain carbon (C) atoms.
It's not like organic farming at all. When you think of fats, you should know that they are lipids. Lipids are
also used to make steroids and waxes. So, if you pick out some earwax and smell it, that's a lipid, too!
Get the Wax Out of Your Ears
Waxes are used to coat and protect things in nature. Bees make wax. It can be used for structures, such
as the bees' honeycombs. Your ears make wax. It is used to protect the inside of your ear. Plants use
wax to stop evaporation of water from their leaves. There is a compound called cutin that you can find in
the plant cuticle covering the surface of leaves. It helps to seal and protect plant structures. Don't worry
about plants being able to breathe. There are still small holes that let gases in and out of the leaves.
Steroids
Steroids are found in animals within something called hormones. The basis of a
steroid molecule is a four-ring structure: one ring with five carbons and three rings
with six carbons. You may have heard of steroids in the news. Many bodybuilders
and athletes have used anabolic steroids to build muscle mass. The steroids make
their bodies add more muscle than they would normally be able to. Those anabolic
steroids help bodybuilders wind up stronger and bulkier (but not faster). Steroids are
also used in necessary medicines. Some help people with acne, while others are
used as muscle relaxers for injuries.
NOTE: Never take drugs to enhance your body. Those athletes are actually hurting their bodies. They
can't see it, because it is slowly destroying their internal organs and not the muscles. When they get
older, they can have kidney and liver problems. Some even die.
Triglycerides
Fat is also known as a triglyceride. It is made up of a molecule
known as glycerol that is connected to one, two, or three fatty
acids. Glycerol is the basis of all fats and is made up of a threecarbon chain that connects the fatty acids together. A fatty acid is
just a long chain of carbon atoms connected to each other.
Saturated and Unsaturated
There are two kinds of fats, saturated and unsaturated.
Unsaturated fats have at least one double bond in one of the fatty
acids. A double bond happens when four electrons are shared or
exchanged in a bond. They are much stronger than single bonds with only two electrons. Saturated fats
have no double bonds.
Fats have a lot of energy stored up in their molecular bonds. That's why the human body stores fat as an
energy source. When you have extra sugars in your system, your body converts them into fats. When it
needs extra fuel, your body breaks down the fat and uses the energy. Where one molecule of sugar only
gives a small amount of energy, a fat molecule gives off many times more.
PROTEINS:
Acids in Proteins?
The first thing you might be asking is, "What is an amino acid?" There are more than fifty, and each one of
them is a little different. Amino acids are used in every cell of your body to build the proteins you need to
survive. All organisms need some proteins, whether they are used in muscles or as simple structures in
the cell membrane. Even though all organisms have differences, they still have one thing in common: the
need for basic chemical building blocks.
Amino acids have a two-carbon bond. One of the carbons is part
of a group called the carboxyl group (COO-). A carboxyl group is
made up of one carbon (C) and two oxygen (O) atoms. That
carboxyl group has a negative charge, since it is a carboxylic acid
(-COOH) that has lost its hydrogen (H) atom. What is left — the
carboxyl group — is called a conjugate base. The second carbon
is connected to the amino group. Amino means there is an NH2
group bonded to the carbon atom. In the image, you see a "+" and
a "-". Those positive and negative signs are there because, in
amino acids, one hydrogen atom moves to the other end of the
molecule. An extra "H" gives you a positive charge.
Making Chains
Even though scientists have discovered over 50 amino acids, only 20 are used to make something called
proteins in your body. Of those twenty, nine are defined as essential. The other eleven can be
synthesized by an adult body. Thousands of combinations of those twenty are used to make all of the
proteins in your body. Amino acids bond together to make long chains. Those long chains of amino acids
are also called proteins.
Essential Amino Acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine,
Tryptophan, and Valine.
Nonessential Amino Acids: Alanine, Asparagine, Aspartic Acid, Glutamic Acid.
Conditional Amino Acids: Arginine (essential in children, not in adults), Cysteine, Glutamine, Glycine,
Proline, Serine, and Tyrosine.
Something Called Side Groups
The side groups are what make each amino acid different
from the others. Of the 20 side groups used to make proteins,
there are two main groups: polar and non-polar. These
names refer to the way the side groups, sometimes called "R"
groups, interact with the environment. Polar amino acids like to
adjust themselves in a certain direction. Non-polar amino acids
don't really care what's going on around them. The polar and
nonpolar chemical traits allow amino acids to point towards
water (hydrophilic) or away from water (hydrophobic). The growing chains can then begin to twist and
turn when they are being synthesized.
Twenty Amino Acids
There are twenty amino acids required for human life to exist. Adults need nine essential amino acids
that they cannot synthesize and must get from food. The other eleven can be produced within our
bodies. In addition to these amino acids, there are some others found in nature (and some very small
amounts in us). These twenty are the biggies to our species and defined as the standard amino acids..
Alanine
Leucine
Arginine
Lysine
Asparagine
Methionine
Aspartic Acid
Phenylalanine
Cysteine
Proline
Glutamic Acid
Serine
Glutamine
Threonine
Glycine
Tryptophan
Histidine
Tyrosine
Isoleucine
Valine
Proteins are made of amino acids. Even though a protein can be very complex, it is basically a long chain
of amino acid subunits all twisted around like a knot.
Primary Structure
As proteins are being built, they begin as a straight chain of amino acids. This chain structure is called the
primary structure. Sometimes chains can bond to each other with two sulfur (S) atoms. Those bonds would
be called a disulfide bridge.
Secondary Structure
After the primary structure comes the secondary structure. The original chain begins to twist. It's as if you
take a piece of string and twist one end. It slowly begins to curl up. In the amino acid chain, each of the
amino acids interacts with the others and it twists like a corkscrew (alpha helix) or it takes the shape of a
folded sheet (beta sheet). We talked about amino acids that are hydrophobic and hydrophilic. Those
desires to stay away or be close to water (H2O) play a part in the twisting.
Tertiary Makes Step Three
Let's move on to the tertiary structure of proteins. By now you're probably getting the idea that proteins do
a lot of folding and twisting. The third step in the creation of a protein is the tertiary structure. The amino
acid chains begin to fold even more and bond using more bridges (the disulfide bridges).
Quaternary Is Fourth and Final
We can finally cover the quaternary structure of proteins. Quaternary means four. This is the fourth phase
in the creation of a protein. In the quaternary structure, several amino acid chains fromthe tertiary
structures fold together in a blob. You heard us right. "Blob" is the term we use on this site. They wind,
entwined, in and out of each other. Some of the most famous protein blobs are hemoglobin in human red
blood cells and the photosystems in plant chloroplasts.
NUCLEIC ACIDS:
The Nucleic Acids
The nucleic acids are the building blocks of living organisms. You may have heard of DNA described the
same way. Guess what? DNA is just one type of nucleic acid. Some other types are RNA, mRNA, and
tRNA. All of these "NAs" work together to help cells replicate and build
proteins. NA? Hold on. Might that stand for nucleic acid? It might.
While you probably don't have to remember the full words right now,
we should tell you that DNA stands for deoxyribonucleic acid. RNA
stands for ribonucleic acid. The mRNA and tRNA are messenger
RNA and transfer RNA, respectively. You may even hear about rRNA
which stands for ribosomal RNA. They are called nucleic acids
because scientists first found them in the nucleus of cells. Now that we
have better equipment, nucleic acids have been found in mitochondria,
chloroplasts, and cells that have no nucleus, such as bacteria and viruses.
The Basics
We already told you about the biggie nucleic acids (DNA, mRNA, tRNA). They are actually made up of
chains of base pairs of nucleic acids stretching from as few as three to millions. When those pairs
combine in super long chains (DNA), they make a shape called a double helix. The double helix shape is
like a twisty ladder. The base pairs are the rungs. We're very close to talking about the biology of cells
here. While it doesn't change your knowledge of the chemistry involved, know that DNA holds your
genetic information. Everything you are in your body is encoded in the DNA found in your cells. Scientists
still debate how much of your personality is even controlled by DNA. Back to the chemistry...
Five Easy Pieces
There are five easy parts of nucleic acids. All nucleic acids are made
up of the same building blocks (monomers). Chemists call the
monomers "nucleotides." The five pieces are uracil, cytosine,
thymine, adenine, and guanine. No matter what science class you
are in, you will always hear about ATCG when looking at DNA. Uracil is
only found in RNA. Just as there are twenty (20) amino acids needed
by humans to survive, we also require five (5) nucleotides.
These nucleotides are made of three parts:
1. A five-carbon sugar
2. A base that has nitrogen (N) atoms
3. An ion of phosphoric acid known as phosphate (PO43-)