"He said science was going to discover the basic secret of life someday,"
the bartender put in. He scratched his head and frowned. "Didn't I
read in the paper the other day where they'd found out what it was?"
"I missed that," I murmured.
"I saw that," said Sandra. "About two days ago."
"That's right," said the bartender.
"What is the secret of life?" I asked.
"I forget," said Sandra.
"Protein," the bartender declared. "They found out something
"Yeah," said Sandra, "that's it."
-Kurt Vonnegut, Jr. Cat's Cradle
Campbell et al., part of Chapter 5
Proteins and nucleic acids make up 2/3 of dry weight of the body
short = "Peptides", medium = polypeptide, long = "protein"
Proteins are very important because chains of amino acids can be very complex
The general formula is NH2-CR-COOH - amino ( -NH2 ) and acid ( -COOH ).
Peptide bonds TRANSPARENCY Fig. (5.16) involves -NH2 and -COOH getting linked
with a dehydration synthesis.
There are about 20 amino acids TRANSPARENCY (Fig. 5.15). (alphabet of 20
R group varies, see figure.
If you made a peptide 4 amino acids long, there would be 20 x 20 x 20 x
20 = 160,000 different possibilities, hence the complexity.
About half of the amino acids are "essential" meaning that they
cannot be made by metabolic conversion from other molecules and thus need
to be eaten TRANSPARENCY (Look ahead to Fig. 41.4 - corn is notoriously
low in tryptophan and methionine).
primary (the sequence) TRANSPARENCY (Fig. 5, 18)
secondary (alpha helix, beta pleated sheet) TRANSPARENCY (Fig. 5-20)
tertiary structure (disulfide and other bonds) TRANSPARENCY (Fig. 5.22)
quaternary structure (chains interact with each other) TRANSPARENCY (Fig.
5.23 - here is a really important example - hemoglobin - which has 2 alpha
subunits and 2 beta subunits.)
There are so many levels of protein structure above these 4, glycosylation
(adding a sugar), phosphorylation, chopping fragments out of the protein,
and other post-translational modifications, that you will have to wait until
a more advanced course to really focus on them.
Protein diversity makes for individuality, and at the level of the immune
system, proteins (antigens) determine self vs non-self.
TRANSPARENCY (Table 5.1)Proteins can serve for:
Structure (example keratin which is in hair)
Enzymes - Their names end in the suffix -ase), that are catalysts (molecules
that influece the rate of a reaction).
Antibodies (used against antigens)
Transport (example hemoglobin)
Motility and contraction
Hormones and neurotransmitters (often smaller fragments of a larger precursor,
Receptors (for hormones and neurotransmitter)
Energy - though the use of protein for energy is not efficient and NH3,
released in catabolism of amino acids, is toxic and must be eliminated,
sometimes as urea, sometimes as uric acid.
Especially as the focus is on proteins (this outline) and nucleic acids
(soon) the field is usually called "biochemistry" or "biological
chemistry." Cellular Biochemistry & Molecular Biology (BL-A302)
(3 credit hours) is offered Fall semester (this year by Profs. Medoff
and Bruzzini). It is
geared to sophomores and is required of Biology majors (BS and BA).
This page was last updated 7/22/02
return to Bio
return to Stark home page