Download All About Proteins Proteins are highly folded polymers constructed

All About Proteins
Proteins are highly folded polymers constructed from monomers called amino acids.
There are 20 Amino Acids and ALL have the
same structure except for the R group or side
chain. Notice the variety in the R groups
shown below – and no, you do NOT need to
memorize them. You DO need to recognize
and be able to draw the general structure of an
amino acid shown at left.
The R groups are important because they may
make an amino acid nonpolar, or polar, and
some of the polar ones may become charged
in water or act as acids or bases. These
properties will play a role in helping the finished protein form.
Amino acids by themselves are of no use to organisms. Instead, they must be formed into
proteins. This process involves several stages. First, a polypeptide must be formed. We pretty
much know how to do this – dehydration synthesis! Just as the process of building a triglyceride
from glycerol and fatty acids looked a bit different from what you learned about joining
monosaccharides, peptide bonding uses still different groups to provide the hydrogens and
oxygen. However, once the bond is formed, a molecule of water will be made as a byproduct.
How many peptide bonds are needed to link together 3 amino acids?
How is the linking together of amino acids different from linking together carbs and lipids parts?
Notice that the amino acids will always be lined up in the same way when creating a polypeptide.
The amino group will always be left intact on the first amino acid in the chain, and the carboxyl
group will be left on the last amino acid. This lets us define which amino acid is first in line and
which is the last, as well as the position of every amino acid in between. This can be absolutely
critical for making a complete and functional protein.
How do we go from a polypeptide to a protein?
The short answer is… very carefully! Lots of twisting and folding is required and a complex set
of rules guides all this action. A finished protein can be described in terms of its level of
structure.
Four Levels of protein structure
Basically, what you need to know
for this class is the following:
1) The order of amino acids
(primary structure)
determines EVERYTHING
ELSE!!!!! It is the unique
characteristics of the
individual amino acids that
causes the chain to start
folding up in a specific shape.
2) If you change the order of
amino acids, you can change
the structure of the final
protein. This can mean the
difference between curly hair
or straight hair.
3) A proteins shape determines
it function. If made
incorrectly, it can result in
terrible consequences for the
organisms. This is basis for
genetic diseases we will talk
about this year.
4) We “know” how to put
together the right amino
acids to build a specific
protein because the
information is coded in our DNA!
Essential vs. Non-essential Amino Acids
Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure
to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in
degradation of the body's proteins—muscle and so forth—to obtain the one amino acid that is
needed. Unlike fat and starch, the human body does not store excess amino acids for later use—
the amino acids must be in the food every day.
?The essential amino acids are arginine (required for the young, but not for adults), histidine,
isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These
amino acids are required in the diet. Plants, of course, must be able to make all the amino acids.
Humans, on the other hand, do not have all the enzymes required for the biosynthesis of all of the
amino acids.
Since the foods we eat contain complete proteins and
not just amino acids, what process occurs during
digestion to free the individual amino acids?
Why might it be important for someone who is
training heavily for an athletic season to eat large
amount of protein in their diet?
Functions of Proteins
Making a complete protein properly is obviously a complex process, and it provides virtually no
limit to the shapes that can be formed. That is why we will not ask you to memorize a standard
form for a complete protein – there isn’t one!
Given all the complexity that is possible, you might guess that proteins can do many different
jobs and you would be correct. A few important functions of proteins are as follows. Look up on
the internet what each of these means in terms of a biological context.
Enzymes:
Structural proteins (collagen, cartialage):
Contractile proteins (actin/myosin):
Chemical messengers (hormones):
Receptors:
Membrane transport proteins:
Defense (Antibodies):