Untitled - Kelly Walsh High School

314 CHEMISTRY FOR THE UTTERLY CONFUSED
The amino acids link together by the reaction of an amino group of one amino
acid with the carboxylic acid group of another amino acid. This forms a
peptide bond. (For the sake of clarity the signs in the reaction have been omitted.)
A peptide bond is an amide group in molecules that are not biochemical.
Many functional groups have different names in organic chemistry and in
biochemistry.
O
C O
H
H
N
H
leaves as H 2 O
There are 20 amino acids found in the human body that are involved in protein
synthesis. Refer to your textbook for a table of the 20 amino acids. The
sequence of the amino acids dictates the properties of a protein. Examples of
proteins include keratin in hair, hemoglobin, insulin, antibodies, and enzymes.
21-6 Carbohydrates
Carbohydrates are made entirely of carbon, hydrogen, and oxygen. The simplest
class of carbohydrates is the monosaccharides. Glucose, C 6H 12O 6, is an
example of a monosaccharide. We can make a disaccharide by joining two
monosaccharides. Examples of disaccharides include sucrose, and lactose. We
can make a polysaccharide, such as starch or cellulose, by joining large numbers
of monosaccharide units together.
The monosaccharides have a couple of characteristics that prove to be important
in terms of their structure and function. They all have at least one carbon
that is bonded to four different groups (a chiral carbon), and most form fiveand
six-membered rings easily. The presence of chiral carbons allows these
compounds to exist as two different optical isomers that are nonsuperimposable
mirror images of each other. (Your feet are nonsuperimposable mirror images.
Try putting a left shoe on a right foot!)
Glucose may form a chain type structure such as the one pictured below. All of
the carbon atoms except the one at the top and the one at the bottom are chiral.
The four different groups making the fourth carbon chiral are outlined.
O
C
N
H