Chapter 19 Amino Acids and
Proteins
19.5
Protein Structure: Tertiary
and Quaternary Levels
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
1
Essential Amino Acids
 are the ten amino acids not
synthesized by the body
 must be obtained from the
diet
 are in meat and diary
products
 are missing (one or more) in
grains and vegetables
 Vegetarians needs
complementary diet:
Wheat/Rice/Oats plus
Means/Peas/Soy
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
2
Tertiary Structure
The tertiary structure of a protein
 gives a specific three-dimensional shape to the
polypeptide chain
 involves interactions and cross-links between
different parts of the peptide chain
 is stabilized by:
hydrophobic and hydrophilic interactions
salt bridges
hydrogen bonds
disulfide bonds
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
3
Tertiary Structure (continued)
 The interactions
of the R groups
give a protein
its specific
threedimensional 3o
structure.
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
4
Cross-Links in Tertiary Structures
General, Organic, and Biological Chemistry
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5
Globular Proteins
Globular proteins
 have compact,
spherical shapes
 carry out synthesis,
transport, and
metabolism in the cells
 Eg: Myoglobin store
and transport oxygen
in muscle
Myoglobin
153 AA,
17,699 dalton
General, Organic, and Biological Chemistry
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6
Fibrous Proteins:
Structure for cells & tissues
Fibrous proteins
 consist of long, fiber-like shapes
 α-keratins make up outer layer of
skin, hair, nails, horns (outer layer)
- 3 α-helices coil to form filament
(held by –S-S- bonds)
contains some β-pleated protein.
- fibrils bundled to a hair strand
 β-keratins make up feathers, beaks.
scales and claws of reptiles
- more β-sheets than α-helices.
- harder/tougher than α-keratins.
General, Organic, and Biological Chemistry
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7
Chitins : a modified polysaccharide
as tough as keratins
Polymer of A amino sugar
N-Acetylglucosamine,
(C6H13O5N)n
 cell walls of fungi, exoskeletons of
arthropods such as crustaceans
(e.g., crabs, lobsters and shrimps)
and insects, the radulas of
mollusks, and the beaks and
internal shells of cephalopods
 Chitosan:
Poly D-Glucosamine,
General, Organic, and Biological Chemistry
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8
Learning Check
Select the type of tertiary interaction as:
1) disulfide
2) ionic
3) H bonds
4) hydrophobic
A.
B.
C.
D.
leucine and valine
two cysteines
aspartic acid and lysine
serine and threonine
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
9
Solution
Select the type of tertiary interaction as:
1) disulfide
2) ionic
3) H bonds
4) hydrophobic
4
1
2
3
A.
B.
C.
D.
leucine and valine
two cysteines
aspartic acid and lysine
serine and threonine
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
10
Quaternary Structure
The quaternary structure
 is the combination of two or
more tertiary units
 is stabilized by the same
interactions found in tertiary
structures
 of hemoglobin consists of
two alpha chains and two
beta chains with heme
groups in each subunit that
pick up oxygen for transport
in the blood to the tissues
General, Organic, and Biological Chemistry
Hemoglobin
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11
Summary of Protein Structures
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
12
Summary of Protein Structures (cont’d)
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
13
Learning Check
Identify the level of protein structure as:
1) primary
2) secondary
3) tertiary
4) quaternary
A.
B.
C.
D.
E.
beta-pleated sheet
order of amino acids in a protein
a protein with two or more peptide chains
the shape of a globular protein
disulfide bonds between R groups
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
14
Solution
Identify the level of protein structure as:
1) primary
2) secondary
3) tertiary
4) quaternary
2
1
4
3
3
A.
B.
C.
D.
E.
beta-pleated sheet
order of amino acids in a protein
a protein with two or more peptide chains
the shape of a globular protein
disulfide bonds between R groups
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
15