Document ID: ./input/supremecourt_opinions/opinions/12pdf/12-398_1B7D.pdf
Page Number: 6.0

Cite as:  569 U. S. ____ (2013) 

3 

Opinion of the Court 

it  was  created.  Pre-RNA  still  contains  nucleotides  corre-
sponding to both the exons and introns in the DNA mole-
cule.  The  pre-RNA  is  then  naturally  “spliced”  by  the 
physical removal of the introns.  The resulting product is a 
strand  of  RNA  that  contains  nucleotides  corresponding 
only  to  the  exons  from  the  original  DNA  strand.    The 
exons-only  strand  is  known  as  messenger  RNA  (mRNA),
which creates amino acids through translation.  In trans-
lation,  cellular  structures  known  as  ribosomes  read  each 
set  of  three  nucleotides,  known  as  codons,  in  the  mRNA. 
Each  codon  either  tells  the  ribosomes  which  of  the  20 
possible  amino  acids  to  synthesize  or  provides  a  stop 
signal that ends amino acid production. 

DNA’s  informational  sequences  and  the  processes  that 
create  mRNA,  amino  acids,  and  proteins  occur  naturally 
within  cells.  Scientists  can,  however,  extract  DNA  from 
cells  using  well  known  laboratory  methods.    These  meth-
ods  allow  scientists  to  isolate  specific  segments  of  DNA—
for  instance,  a  particular  gene  or  part  of  a  gene—which
can then be further studied, manipulated, or used.  It is also 
possible  to  create  DNA  synthetically  through  processes 
similarly  well  known  in  the  field  of  genetics.   One  such 
method  begins  with  an  mRNA  molecule  and  uses  the 
natural bonding properties of nucleotides to create a new,
synthetic  DNA  molecule.  The  result  is  the  inverse  of  the 
mRNA’s  inverse  image  of  the  original  DNA,  with  one
important  distinction:  Because  the  natural  creation  of
mRNA involves splicing that removes introns, the synthetic
DNA  created  from  mRNA  also  contains  only  the  exon 
sequences.   This  synthetic  DNA  created  in  the  laboratory
from mRNA is known as complementary DNA (cDNA).

Changes  in  the  genetic  sequence  are  called  mutations. 
Mutations  can  be  as  small  as  the  alteration  of  a  single 
nucleotide—a change affecting only one letter in the genetic 
code.  Such  small-scale  changes  can  produce  an  entirely 
different  amino  acid  or  can  end  protein  production  alto-