The Structure and Function of Large Biological Molecules

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Fig. 5-21b

Amino acid

subunits

+H3N

Amino end

Carboxyl end

125

120

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110

105

100

95

90

85

80

75

20

25

15

10

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1

Slide 79

The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone

Typical secondary structures are a coil called an  helix and a folded structure called a  pleated sheet

Animation: Secondary Protein Structure

Slide 80

Fig. 5-21c

Secondary Structure

 pleated sheet

Examples of

amino acid

subunits

 helix

Slide 81

Fig. 5-21d

Abdominal glands of the

spider secrete silk fibers

made of a structural protein

containing  pleated sheets.

The radiating strands, made

of dry silk fibers, maintain

the shape of the web.

The spiral strands (capture

strands) are elastic, stretching

in response to wind, rain,

and the touch of insects.

Slide 82

Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents

These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions

Strong covalent bonds called disulfide bridges may reinforce the protein’s structure

Animation: Tertiary Protein Structure

Slide 83

Fig. 5-21e

Tertiary Structure

Quaternary Structure

Slide 84

Fig. 5-21f

Polypeptide

backbone

Hydrophobic

interactions and

van der Waals

interactions

Disulfide bridge

Ionic bond

Hydrogen

bond

Slide 85

Fig. 5-21g

Polypeptide

chain

 Chains

Heme

Iron

 Chains

Collagen

Hemoglobin

Slide 86

Quaternary structure results when two or more polypeptide chains form one macromolecule

Collagen is a fibrous protein consisting of three polypeptides coiled like a rope

Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains

Animation: Quaternary Protein Structure

Slide 87