Download 3 Formation Peptides GOB Structures

19.3 Formation of Peptides
A peptide bond is an amide bond that forms when the — COO− group of
one amino acid reacts with the — NH3+ group of the next amino acid.
The linking of two or more amino acids by peptide bonds forms a peptide.
Learning Goal Draw the structure for a peptide, give its
three-letter and one-letter abbreviations, and name.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Formation of Peptides
The linking of two or more amino acids by peptide
bonds forms a peptide.
Peptides formed from
• two amino acids are called dipeptides.
• three amino acids are called tripeptides.
• four amino acids are called tetrapeptides.
• five amino acids are called pentapeptides
• longer chains of amino acids are called
polypeptides.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Formation of Peptides
A peptide bond
• is an amide bond.
• forms between the — COO− group of one amino
acid and the — NH3+ group of the next amino acid.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Guide to Drawing a Peptide
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Draw the dipeptide Ser–Thr.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Draw the dipeptide Ser–Thr.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Naming Peptides
The name of a peptide
• begins with the name of the N-terminal amino acid
residue.
• gives all the following amino acid residues up to the
C-terminal amino acid in which the ine or ate endings
are replaced with yl.
• retains the complete name of the C-terminal amino acid.
A tripeptide consisting of alanine, glycine, and serine
residues is named as
alanylglycylserine
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Draw the structure and give the name for the tripeptide
Gly−Ser−Met.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Draw the structure and give the name for the tripeptide
Gly−Ser−Met.
STEP 1 Draw the structures for each amino acid in the
peptide, starting with the N-terminus.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Draw the structure and give the name for the tripeptide
Gly−Ser−Met.
STEP 2 Remove the O atom from the carboxylate group
of the N-terminal amino acid and two H atoms
from the ammonium group in the adjacent amino
acid. Repeat this process until the C-terminus is
reached.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Draw the structure and give the name for the tripeptide
Gly−Ser−Met.
STEP 3 Use peptide bonds to connect the amino acid
residues.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Draw the structure and give the name for the tripeptide
Gly−Ser−Met.
The tripeptide is named by
• replacing the last syllable of each amino acid name with yl,
starting with the N-terminus.
The C-terminus retains its complete amino acid name.
N-terminus glycine is named glycyl; serine is
named seryl.
C-terminus methionine keeps its full name.
The tripeptide is named glycylserylmethionine.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.