cellular processes would 
proceed slowly or not at 
all. According to chemist 
Ronald Breslow of 
Columbia University, 
enzymes work so well 
that a process that takes 
5 seconds (such as read- 
ing this sentence) with 
enzymes would take 
1,500 years without 
them. Enzymes can do 
their jobs — often, cutting 
apart or splicing together 
other molecules — over 
and over. They also have 
great specificity. Like a 
lock, each enzyme will 
accept only appropriately 
shaped “keys” (called 
substrates). Each cell 
contains thousands of 
kinds of enzymes. 
Once a protein is purified, 
the sequence in which 
the amino acids occur on 
the chain can be deter- 
mined. Knowing the 
amino acid sequence of a 
protein is extremely 
important for many 
reasons. For example, it 
may help scientists 
synthesize large quantities 
of the protein for 
research or commercial 
purposes. Direct sequenc- 
ing of a protein, although 
much quicker and more 
accurate now due to the 
development of automated 
equipment, is an enor- 
mously time-consuming 
task. It is technically 
easier to sequence the 
DNA of the gene that 
codes for the protein. 
For this reason, in most 
cases protein sequencing 
has been replaced by 
isolating, cloning, and 
sequencing a gene by 
recombinant DNA 
techniques. The protein 
sequence is then inferred 
from the DNA sequence 
that codes for it. 
Even if the sequence of 
amino acids in a protein 
is known, scientists 
cannot predict how the 
protein will fold into its 
final, active shape. Many 
researchers are working 
to solve this so-called 
“folding problem.” 
They feel that if they 
can learn the rules by 
which proteins fold, it 
will open the way to 
synthesizing engineered, 
artificial proteins with 
many therapeutic, 
industrial, and manufac- 
turing applications. 
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