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Lecture 9
Proteins
Pp47-53
Proteins
• One of these most important components of
the body
• Diverse functions
– Structure
– Movement
– Protection
– Enzymes
Communication
Binding
Recognition
Transport
Structure
– Keratin
• Nails, hair, surface skin
Kangaroo Rat kidney epithelial cell
Structure
• Cell Structure
Movement
– Muscle movement
– Intracellular transport
• Actin, myosin, microtubules
Communication
– Some hormones
– Cell to cell signals
Catalysts
– Enzymes
• Pepsin
• Lactase
• Trypsin
Cell Adhesion
• Binds cells together
– Sperm and egg
– Immune cells to harmful cells
Human Sperm and Egg
Recognition and Protection
•
•
•
•
Glycoproteins
Immune recognition
Antibodies
Clotting Proteins
Influenza virus EM
Blood clot
3.3 Cells make a huge number of large molecules from
a small set of small molecules
• The four classes of biological molecules contain
very large molecules
– They are often called macromolecules because of
their large size
– They are also called polymers because they are
made from identical building blocks strung together
– The building blocks are called monomers
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Building Blocks
• A chain of carbon atoms is called a carbon
skeleton
Copyright © 2009 Pearson Education, Inc.
Starch granules in
potato tuber cells
STARCH
Glucose
monomer
Neutral Fats (Triglycerides)
• Composed of three fatty acids bonded to a
glycerol molecule
Figure 2.15a
Amino Acids
• Building blocks of protein, containing an
amino group and a carboxyl group
• Amino group NH2
• Carboxyl groups COOH
• All contain:
– Central Carbon
– Hydrogen
– Amino group (-NH2)
– Carboxyl group (-COOH)
– R group (Radical group)
• Makes amino acids different from each other
• All contain:
– Central Carbon
– Hydrogen
– Amino group (-NH2)
– Carboxyl group (-COOH)
– R group (Radical group)
• Makes amino acids different from each other
• All contain:
– Central Carbon
– Hydrogen
– Amino group (-NH2)
– Carboxyl group (-COOH)
– R group (Radical group)
• Makes amino acids different from each other
• All contain:
– Central Carbon
– Hydrogen
– Amino group (-NH2)
– Carboxyl group (-COOH)
– R group (Radical group)
• Makes amino acids different from each other
• All contain:
– Central Carbon
– Hydrogen
– Amino group (-NH2)
– Carboxyl group (-COOH)
– R group (Radical group)
• Makes amino acids different from each other
R groups
• Can be hydrophobic or hydrophilic
• Vary in size
– Small = H, glycine
– Large = rings, tryptophan
H
H
Glycine
Amino Acids
Figure 2.16a–c
Amino Acids
Figure 2.16d, e
3.12 Proteins are made from amino acids linked by
peptide bonds
• Amino acids are classified as hydrophobic or
hydrophilic
– Some amino acids have a nonpolar R group and are
hydrophobic
– Others have a polar R group and are hydrophilic, which
means they easily dissolve in aqueous solutions
Copyright © 2009 Pearson Education, Inc.
Leucine (Leu)
Hydrophobic
Serine (Ser)
Aspartic acid (Asp)
Hydrophilic
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Figure 2.17
Linking amino acids
• Peptide = 2 or more amino acids bonded
together
• Peptide bond
– Condensation (dehydration) reaction
– Links an amino group of one amino acid to the
carboxyl group of the next amino acid
Peptides
• Dipeptide = 2 amino acids linked together
• Tripeptide = 3 amino acids linked together
• Oligopeptide = Chains of 15 or less amino
acids linked together
• Polypeptide = Chains of more than 15 amino
acids linked together
• Protein = 50 or more amino acids linked
together
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
N
C
C
OH
H
Amino acid
Dehydration H O
2
synthesis
Hydrolysis
H
H2O
H
R
O
H
R
O
N
C
C
N
C
C
H
H
OH
Dipeptide
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
N
C
C
OH
H
Amino acid
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
N
C
C
Dehydration H O
2
synthesis
OH
H
Amino acid
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
N
C
C
OH
H
Amino acid
Dehydration H O
2
synthesis
H
H
R
O
H
R
O
N
C
C
N
C
C
H
H
OH
Dipeptide
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
H
H
R
O
H
R
O
N
C
C
N
C
C
H
H
OH
Dipeptide
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
Hydrolysis
H
H2O
H
R
O
H
R
O
N
C
C
N
C
C
H
H
OH
Dipeptide
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
H
R
O
H
R
O
N
C
C
N
C
C
N
C
C
OH
H
Amino acid
Hydrolysis
H
H2O
H
H
OH
Dipeptide
Figure 2.17
Protein
• Macromolecules composed of combinations
of 20 types of amino acids bound together
with peptide bonds
Peptide bond
H
H
R
O
N
C
C
OH
H
Amino acid
+
H
H
R
O
N
C
C
OH
H
Amino acid
Dehydration H O
2
synthesis
Hydrolysis
H
H2O
H
R
O
H
R
O
N
C
C
N
C
C
H
H
OH
Dipeptide
Figure 2.17
Structure of proteins
• VERY IMPORTANT!!!
• Complex conformation (3-D structure)
• 4 levels of structure:
– Primary
– Secondary
– Tertiary
– Quaternary
Structural Levels of Proteins
• Primary – amino acid sequence
• Secondary – alpha helices or beta pleated
sheets
Structural Levels of Proteins
• Tertiary – superimposed folding of secondary
structures
• Quaternary – polypeptide chains linked
together in a specific manner
Structural Levels of Proteins
Figure 2.18a–c
Structural Levels of Proteins
Figure 2.18b,d,e
Four Levels of Protein Structure
Primary structure
Amino acids
Four Levels of Protein Structure
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
Pleated sheet
Four Levels of Protein Structure
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
Tertiary structure
Polypeptide
(single subunit
of transthyretin)
Pleated sheet
Four Levels of Protein Structure
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
Tertiary structure
Quaternary structure
Polypeptide
(single subunit
of transthyretin)
Transthyretin, with
four identical
polypeptide subunits
Pleated sheet
Amino acids
Primary structure
Amino acids
Hydrogen
bond
Alpha helix
Secondary structure
Pleated sheet
Polypeptide
(single subunit
of transthyretin)
Tertiary structure
Transthyretin, with
four identical
polypeptide subunits
Quaternary structure
Fibrous and Globular Proteins
• Fibrous proteins
– Extended and strand-like proteins
– Examples: keratin, elastin, collagen, and certain
contractile fibers
Fibrous and Globular Proteins
• Globular proteins
– Compact, spherical proteins with tertiary and
quaternary structures
– Examples: antibodies, hormones, and enzymes
Table 2.3.1
Table 2.3.2
Protein Denuaturation
• Reversible unfolding of proteins due to drops
in pH and/or increased temperature
Figure 2.19a
Protein Denuaturation
• Irreversibly denatured proteins cannot refold
and are formed by extreme pH or temperature
changes
Figure 2.19b
Molecular Chaperones (Chaperonins)
• Help other proteins to achieve their functional
three-dimensional shape
• Maintain folding integrity
• Assist in translocation of proteins across
membranes
• Promote the breakdown of damaged or
denatured proteins
Molecular Chaperones
(Chaperonins)
• Help other proteins to achieve their functional
three-dimensional shape
• Maintain folding integrity
• Assist in translocation of proteins across
membranes
• Promote the breakdown of damaged or
denatured proteins
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