Download Primary Structure of Proteins

19.4 Protein Structure: Primary
and Secondary Levels
The secondary structure of a
protein describes the structure
that forms when amino acids
form hydrogen bonds between
the atoms in the backbone and
atoms on the same or another
peptide chain.
The secondary structure in silk
is a β-pleated sheet.
Learning Goal Describe the primary and secondary
structures of a protein.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Primary Structure of Proteins
A protein is a polypeptide of 50 or more amino acids with
biological activity.
The primary structure of a protein is the particular sequence
of amino acids held together by peptide bonds.
Ala–Leu–Cys–Met
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Primary Structure
A thyroid hormone that stimulates the release of thyroxin is a
tripeptide with the amino acid sequence Glu–His–Pro, EHP.
Although other amino acid sequences of these three amino
acids are possible, only the specific sequence or primary
structure of Glu−His−Pro produces hormonal activity.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Primary Structure of Insulin
Insulin
• was the first protein to have its
primary structure determined.
• has a primary structure of two
polypeptide chains linked by
disulfide bonds.
• has a chain A with 21 amino acids
and a chain B with 30 amino acids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Answer the questions
for the following tripeptide:
A. What is the N-terminus?
B. What is the C-terminus?
C. What is the name of the tripeptide?
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Answer the questions
for the following tripeptide:
A. What is the N-terminus? Phe
B. What is the C-terminus? Ala
C. What is the name of the tripeptide?
phenylalanylcystylalanine
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Write the names and three-letter abbreviations of
the tripeptides that could form from two glycines
and one alanine.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Write the names and three-letter abbreviations of
the tripeptides that could form from two glycines
and one alanine.
Glycylglycylalanine
Gly–Gly–Ala
Glycylalanylglycine
Gly–Ala–Gly
Alanylglycylglycine
Ala–Gly–Gly
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.