Download - Amino Acids Proteins, and Enzymes
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Amino Acids Proteins, and Enzymes
Types of Proteins
Amino Acids
The Peptide Bond
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Types of Proteins
Type Examples• Structural tendons, cartilage, hair, nails• Contractile muscles• Transport hemoglobin• Storage milk• Hormonal insulin, growth hormone• Enzyme catalyzes reactions in cells• Protection immune response
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Amino Acids
• Building blocks of proteins• Carboxylic acid group• Amino group• Side group R gives unique characteristics
R side chain I
H2N—C —COOH I
H
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Examples of Amino Acids
H I
H2N—C —COOH I
H glycine
CH3 I
H2N—C —COOH I
H alanine
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Types of Amino Acids
Nonpolar R = H, CH3, alkyl groups, aromatic
OPolar ll
R = –CH2OH, –CH2SH, –CH2C–NH2,
(polar groups with –O-, -SH, -N-)
Polar/Acidic
R = –CH2COOH, or -COOH
Polar/ Basic
R = –CH2CH2NH2
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Essential Amino Acids
• 10 amino acids not synthesized by the body
• arg, his, ile, leu, lys, met, phe, thr, trp, val
• Must obtain from the diet
• All in diary products
• 1 or more missing in grains
and vegetables
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Amino Acids as Acids and Bases
• Ionization of the –NH2 and the –COOH group
• Zwitterion has both a + and – charge• Zwitterion is neutral overall
+
NH2–CH2–COOH H3N–CH2–COO–
glycine Zwitterion of glycine
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pH and ionization
H+ OH–
+ +
H3N–CH2–COOH H3N–CH2–COO– H2N–CH2–
COO–
Positive ion zwitterion Negative ion
Low pH neutral pH High pH
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The Peptide Bond
Amide bond formed by the –COOH of an amino acid and the –NH2 of the next amino acid
O CH3
+ | | + |
NH3–CH2–COH + H3N–CH–COO–
O CH3
+ | | |
NH3–CH2–C – N–CH–COO–
| peptide bond H
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Peptides
• Amino acids linked by amide (peptide) bonds
Gly Lys Phe Arg Ser
H2N- -COOH
end Peptide bonds end
Glycyllysylphenylalanylarginylserine
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Amino Acids, Proteins, and Enzymes
Primary and Secondary Structure
Tertiary and Quaternary Structure
Protein Hydrolysis and Denaturation
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Primary Structure of Proteins
The particular sequence of amino acids that is the backbone of a peptide chain or protein
H3N CH
CH3
C
O
N
H
CH C
O
N
H
CH C
O
N
H
CH C O-
OCH
CH CH3
CH3
CH2
SH
CH2
CH2
S
CH3
+
Ala-Leu-Cys-Met
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Secondary Structure – Alpha Helix
• Three-dimensional arrangement of amino acids with the polypeptide chain in a corkscrew shape
• Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain
• Looks like a coiled “telephone cord”
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Secondary Structure – Beta Pleated Sheet
• Polypeptide chains are arranged side by side
• Hydrogen bonds form between chains
• R groups of extend above and below the sheet
• Typical of fibrous proteins such as silk
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Secondary Structure – Triple Helix
• Three polypeptide chains woven together
• Glycine, proline, hydroxy proline and hydroxylysine
• H bonding between –OH groups gives a strong structure
• Typical of collagen, connective tissue, skin, tendons, and cartilage
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Tertiary Structure
• Specific overall shape of a protein• Cross links between R groups of amino
acids in chain
disulfide –S–S– +
ionic –COO– H3N–
H bonds C=O HO–
hydrophobic –CH3 H3C–
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Globular and Fibrous Proteins
Globular proteins Fibrous proteins
“spherical” shape long, thin fibers
Insulin Hair
Hemoglobin Wool
Enzymes Skin
Antibodies Nails
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Quaternary Structure
• Proteins with two or more chains• Example is hemoglobin
Carries oxygen in blood
Four polypeptide chains
Each chain has a heme group to
bind oxygen
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Protein Hydrolysis
• Break down of peptide bonds • Requires acid or base, water and
heat• Gives smaller peptides and
amino acids • Similar to digestion of proteins
using enzymes• Occurs in cells to provide amino
acids to synthesize other proteins and tissues
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Hydrolysis of a Dipeptide
H3N CH
CH3
C
O
N
H
CH C
OCH2
OH
OH
+
H3N CH
CH3
COH
O
+ CH C
OCH2
OH
OHH3N
H2O, H+
++
heat
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Denaturation
Disruption of secondary, tertiary and quaternary protein structure byheat/organics
Break apart H bonds and disrupt hydrophobic attractions acids/ bases
Break H bonds between polar R groups andionic bonds
heavy metal ions React with S-S bonds to form solids
agitation Stretches chains until bonds break
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Secondary Structure – Triple Helix
• Three polypeptide chains woven together
• Glycine, proline, hydroxy proline and hydroxylysine
• H bonding between –OH groups gives a strong structure
• Typical of collagen, connective tissue, skin, tendons, and cartilage
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Applications of Denaturation
• Hard boiling an egg• Wiping the skin with alcohol swab for
injection• Cooking food to destroy E. coli.• Heat used to cauterize blood vessels• Autoclave sterilizes instruments• Milk is heated to make yogurt
Functions of Proteins
• Structure – collagen, keratin,elastin• Enzyme – lysozyme, amylase, • Transport – hemoglobin, lipoproteins• Contractile – actin, myosin, tubulin• Hormone – insulin, growth hormone• Antibody – IgG, • Pigment – melanin, rhodopsin• Recognition – CD4, MHC proteins
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