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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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