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Functional Diversity of Proteins

Catalysis: Enzymes: amylase, pepsin, lipase

Transport: hemoglobin, serum albumin

Structure: keratin, collagen

Movement, Contraction: myosin, actin

Defense: antibodies, fibrinogen

Nutrient and Storage: egg albumin, zein

Regulation: hormones (insulin), repressors
Protein Classification by Function
Structure
Transport
Regulation
Motion
Regulation
Catalysis
Defense
Catalysis
Missing Function?
Storage
Classification of Proteins
By Shape
Fibrous -insoluble in water
Functions: structure, motion
High percentage of nonpolar amino acids
Globular -usually soluble in water
Functions: transport, catalysis, storage
Higher percentage of polar and charged
amino acids
Classification of Proteins
By Composition
Simple contain only amino acids
Examples: amylase, pepsin
Conjugated - contain something besides
amino acids
Examples:
Hemoglobin - contains iron
Immunoglobin - contains carbohydrate
Lactate dehydrogenase - contains niacin
-carboxyl
group
-carbon
-amino
group
side chain
Nonpolar Amino Acids
Polar, Uncharged Amino Acids
Polar, Charged Amino Acids
Negatively-charged
Positively-charged
Amino Acid Classification: Functional Group
Sulfhydryl
Alcohol
CO2
+
H 3N
CO2
CO2
C
H
+
H3N
C
CH2
+
H
CH3
Threonine (Thr)
C
H
+
H 3N
C
Cysteine (Cys)
Amide
CO2
H
+
H 3N
C
H
+
H 3N
CO2
C
H
CH2
CH2
CH2
CH2
CO2
CH2
C
Aspartic Acid (Asp)
CO2
NH2
Glutamic Acid (Glu)
H
SH
Carboxylic Acid
CO2
CO2
H 3N
C
CH2
CHOH
OH
Serine (Ser)
+
H 3N
O
Asparagine (Asn)
CH2
C
O
NH2
Glutamine (Gln)
-carboxyl
group
-carbon
-amino
group
side chain
Amino Acid Titration
H
+
H3N
C
H
OH
+
CO2H
CH3
Below
Isoelectric pH
Net Charge +
H3N
H+
C
H
OH
CO2
CH3
Isoelectric pH
Net Charge 0
H2N
H+
C
CO2
CH3
Above
Isoelectric pH
Net Charge –
Titration of Glycine
Isoelectric pH = 6.0
Titration of Glutamic Acid
Isoelectric pH = 3.2
Titration of Histidine
Isoelectric pH = 7.6
Electrophoresis of Amino Acid Mixture at pH 6
Alanine, Arginine, Aspartic Acid
At pH 6
Alanine (pI = 6)
Arginine (pI = 10.8)
Aspartic Acid (pI = 2.8)
Net charge = 0
Net charge is +
Net charge is –
Paper Chromatography of Amino Acids
Asp Gly
Lys
polar amino acids
Leu
Phe Tyr
nonpolar amino acids
Biologically Active Peptides
Impact of changes in amino acids
Vasopressin - Stimulates water reabsorption in the kidney
Oxytocin - Stimulates lactation and uterine contraction
Levels of Protein Structure
Forces Involved in
Protein Structure
Primary Structure
of Insulin
Primary Structure of Lysozyme
Secondary Structure
-Helix
Secondary Structure
-Structure
Collagen
(triple helix)
Elastin Structure
Myoglobin: Secondary and Tertiary Structure
- helix
- helix
Myoglobin
Surface View
Heme Group
Cross-Section
Lysozyme: Secondary and Tertiary Structure
- helix
- structure
Lysozyme: Tertiary Structure
Active Site
Hemoglobin: Quaternary Structure
Heme Group
Sickle-cell Hemoglobin
valine-valine interaction
Electrophoresis of
Hemoglobin A,
Sickle-Cell Hemoglobin,
and Hemoglobin C
Hemoglobin S
Glu to Val at
Position 6 on the
Beta Chain
Hemoglobin C
Glu to Lys at
Position 6 on the
Beta Chain
Protein Denaturation
Denaturation involves
• The disruption of bonds in the secondary, tertiary and
quaternary protein structures.
• Heat and organic compounds that break apart H bonds
and disrupt hydrophobic interactions.
• Acids and bases that break H bonds between polar R
groups and disrupt ionic bonds.
• Heavy metal ions that react with S-S bonds to form
solids.
• Agitation such as whipping that stretches peptide
chains until bonds break.
Applications of Denaturation
Use of 70% ethanol or isopropyl alcohol as a disinfectant
Use of silver nitrate solution in eyes of newborns to
prevent gonorrhea infection
Use of eggs or milk as antidote for heavy metal poisoning
Use of tannic acid in burn ointment to coagulate proteins
at burn site
Use of high temperature to sterilize items
Denaturation and Renaturation of Ribonuclease