Proteins: Form Equals Function
Proteins are chains of amino acids that fold into three-dimensional shapes.
Proteins come in a wide variety of amino acid sequences, sizes, and threedimensional structures, which reflect their diverse roles in nearly all cellular
functions. Each protein has a particular structure necessary to bind and react
with other molecules; thus, function is directly correlated to structure of the
protein.
For example, lactase is a protein (enzyme) that breaks down the sugar found
in dairy products, lactose. Lactase must have a specific 3D shape that fits
with lactose, like two pieces of a puzzle. This is oftentimes compared to a
key fitting into a lock. If the protein doesn’t have the specific shape needed, it
cannot attach to another molecule, and the reaction cannot take place.
Carbohydrates: Form Equals Function
Simple carbohydrates are relatively small molecules that the body can easily
use for cellular respiration (to create ATP, or usable energy). In cellular
respiration, one molecule of glucose can be broken down, therefore releasing
the energy that is stored within the bonds right away.
Complex carbohydrates are polymers made of many simple carbohydrates.
We gave you three examples.
The first, starch, provides energy for the plants that make
them, and starch serves as the main food source for many
animals. Humans and other animals produce enzymes (a
protein) that can break down starch. Because starch is a
long chain of simple carbohydrates, one piece can be
broken off at a time to be used for energy (go through
cellular respiration). In plants, this structure allows starch
to be used throughout the day for energy and not all at once.
The second complex carbohydrate, cellulose, provides
structural support to plants. The monomers in cellulose
form tight bonds, allowing flower stems and tree trunks to
maintain their rigid, straight height. Humans do not produce
an enzyme (a protein) that can digest cellulose, so it passes
through the body undigested (meaning it is never used for
energy because cellular respiration requires a simple carbohydrate).
The third type of complex carbohydrate, glycogen, is a
polymer of glucose and the storage form of carbohydrates in
animals (humans too). When animals eat simple
carbohydrates or starch, not all of the glucose may be needed
right away. Your body will take the extra glucose and build
a complex carbohydrate known as glycogen. This compact
structure allows more glucose to be stored in cells for later
use. Just like starch, the ends of a glycogen molecule can be used for energy
when needed throughout the day. This is why you don’t have to eat food
every time you need energy…your body stores the extra for later!
Lipids (Fats): Form Equals Function
There are many different types of lipids, but the one we are focusing on is the
phospholipid, which is a molecule that makes up the majority of the cell
membrane. An important property of lipid molecules is that they do not mix
well with water. In the cell membrane, the lipid molecules are arranged into
two layers (called the lipid bilayer). The parts of the phospholipids that have
the highest tendency to interact with water (hydrophilic) are located toward
the outside and inside of the cell. The parts of the phospholipids with the
lowest tendency to interact with water (hydrophobic) are located toward the
interior of the membrane. The interior part of the membrane prevents some
molecules from entering the cell.
Nucleic Acids: Form Equals Function
Both DNA and RNA are nucleic acids. They are given this name because
they are made up of nucleotides. The nucleotide is comprised of a phosphatesugar backbone and a nitrogen base as the “steps” of the twisted ladder.
There are four nitrogen bases in DNA: adenine, thymine, cytosine, and
guanine. Most people refer to these using four letters, A, T, C, and G.
For example, to refer to a specific piece of DNA, we might
write: AATTGCCTTTTAAAAA. The sequence of bases
(letters) can code for many properties of the body’s
cells. The cells can read this code. Some DNA
sequences encode important information for the cell.
The DNA code, or genetic code as it is called, is passed through the sperm
and egg to the offspring. A single sperm cell contains about three billion
bases consisting of A, T, G and C that follow each other in a well defined
sequence along the strand of DNA. Each egg cell also contains three billion
bases arranged in a well-defined sequence very similar, but not identical to the
sperm.
In essence, this structure creates compartments that allow each individual cell
to control its internal environment, by letting certain substances move in or
out of the cell. Temperature, water, minerals, nutrients, oxygen, pH levels,
and other balances must be maintained in each cell in order to live. Just think,
the cells in our stomach must maintain a very different environment than the
cells of our heart muscle. We are able to do this because cell membranes are
made out of lipids!
DNA varies from one individual to another. These DNA variations can be
used to identify people or at least distinguish one person from another because
the specific sequence of DNA bases is what makes each person unique.