AP Bio

Protiens ­ Chapter 5 1

8­17­09

Aug 12­8:09 AM

Concept 5.4: Proteins have many structures, resulting in a wide range of functions

• Proteins account for more than 50% of the dry mass of most cells• Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances

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Aug 12­8:09 AM

Table 5­1

hydrolytic enzymes

Aug 12­8:09 AM

• Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions• Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

Animation: Enzymes

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AP Bio

Protiens ­ Chapter 5 2

8­17­09

Aug 12­8:09 AM

Fig. 5­16

Enzyme(sucrase)

Substrate(sucrose)

Fructose

Glucose

OH

H O

H2O

Induced fit model of enzyme activity

EnzymeSubstrate Complex

Aug 12­8:09 AM

Polypeptides

• Polypeptides are polymers built from the same set of 20 amino acids• A protein consists of one or more polypeptides

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

polypeptide chain is astring of amino acids

An active protein might beone chain or many chains

ADH = l ch

ain

Hemoglobi

n = 4 chain

s

Aug 12­8:09 AM

Amino Acid Monomers

• Amino acids are organic molecules with carboxyl and amino groups• Amino acids differ in their properties due to differing side chains, called R groups

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

AP Bio

Protiens ­ Chapter 5 3

8­17­09

Aug 12­8:09 AM

Fig. 5­UN1

Aminogroup

Carboxylgroup

α carbon

Aug 12­8:09 AM

Fig. 5­17Nonpolar

Glycine(Gly or G)

Alanine(Ala or A)

Valine(Val or V)

Leucine(Leu or

L)

Isoleucine

(Ile or I)

Methionine

(Met or M)

Phenylalanine

(Phe or F)

Trypotphan(Trp or W)

Proline(Pro or P)

Polar

Serine(Ser or

S)

Threonine(Thr or T)

Cysteine(Cys or C)

Tyrosine(Tyr or Y)

Asparagine

(Asn or N)

Glutamine

(Gln or Q)Electricall

ychargedAcidi

cBasic

Aspartic acid

(Asp or D)

Glutamic acid

(Glu or E)

Lysine(Lys or K)

Arginine(Arg or R)

Histidine(His or H)

Aug 13­8:47 AM

AP Bio

Protiens ­ Chapter 5 4

8­17­09

Aug 12­8:09 AM

Fig. 5­17a

Nonpolar

Glycine (Gly or G)

Alanine (Ala or A)

Valine (Val or V)

Leucine (Leu or L)

Isoleucine (Ile or I)

Methionine (Met or M)

Phenylalanine (Phe or F)

Tryptophan (Trp or W)

Proline (Pro or P)

Aug 12­8:09 AM

Fig. 5­17c

Acidic

Arginine (Arg or R)

Histidine (His or H)

Aspartic acid (Asp or D)

Glutamic acid (Glu or E)

Lysine (Lys or K)

Basic

Electricallycharged

Aug 12­8:09 AM

Amino Acid Polymers

• Amino acids are linked by peptide bonds• A polypeptide is a polymer of amino acids• Polypeptides range in length from a few to more than a thousand monomers • Each polypeptide has a unique linear sequence of amino acids

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AP Bio

Protiens ­ Chapter 5 5

8­17­09

Aug 12­8:09 AM

Peptidebond

Fig. 5­18

Amino end(N­terminus)

Peptidebond

Side chains

Backbone

Carboxyl end(C­terminus)

(a)

(b)

Aug 12­8:09 AM

Protein Structure and Function

• A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape

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Aug 12­8:09 AM

Fig. 5­19

A ribbon model of lysozyme(a) (b) A space­filling model of lysozyme

GrooveGroove

AP Bio

Protiens ­ Chapter 5 6

8­17­09

Aug 12­8:09 AM

Fig. 5­19a

A ribbon model of lysozyme(a)

Groove

Aug 12­8:09 AM

Fig. 5­19b

(b) A space­filling model of lysozyme

Groove

Aug 12­8:09 AM

• The sequence of amino acids determines a protein’s three­dimensional structure• A protein’s structure determines its function

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

AP Bio

Protiens ­ Chapter 5 7

8­17­09

Aug 12­8:09 AM

Fig. 5­20

Antibody protein Protein from flu virus

Aug 12­8:09 AM

Four Levels of Protein Structure

• The primary structure of a protein is its unique sequence of amino acids• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain• Tertiary structure is determined by interactions among various side chains (R groups)• Quaternary structure results when a protein consists of multiple polypeptide chains

Animation: Protein Structure Introduction

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Aug 12­8:09 AM

• Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word • Primary structure is determined by inherited genetic information

Animation: Primary Protein Structure

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

AP Bio

Protiens ­ Chapter 5 8

8­17­09

Aug 12­8:09 AM

Fig. 5­21

PrimaryStructure

SecondaryStructure

TertiaryStructure

β pleated sheet

Examples ofamino acidsubunits

+H3N Amino end

α helix

QuaternaryStructure

Aug 12­8:09 AM

Fig. 5­21a

Amino acidsubunits

+H3N Amino end

25

20

15

10

5

1Primary Structure

Aug 12­8:09 AM

Fig. 5­21b

Amino acidsubunits

+H3N Amino end

Carboxyl end125

120

115

110

10510

0

95

908

5

80

75

20

25

15

10

5

1

AP Bio

Protiens ­ Chapter 5 9

8­17­09

Aug 12­8:09 AM

• 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 α helix and a folded structure called a β pleated sheet

Animation: Secondary Protein Structure

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Aug 12­8:09 AM

Fig. 5­21c

Secondary Structureβ pleated sheet

Examples ofamino acidsubunits

α helix

Aug 12­8:09 AM

Fig. 5­21d

Abdominal glands of thespider secrete silk fibers

made of a structural proteincontaining b pleated sheets.The radiating strands, madeof dry silk fibers, maintain

the shape of the web.

The spiral strands (capturestrands) are elastic, stretching

in response to wind, rain,and the touch of insects.

AP Bio

Protiens ­ Chapter 5 10

8­17­09

Aug 12­8:09 AM

• 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

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Aug 12­8:09 AM

Fig. 5­21e

Tertiary Structure Quaternary Structure

Aug 12­8:09 AM

Fig. 5­21f

Polypeptidebackbone

Hydrophobicinteractions andvan der Waalsinteractions

Disulfide bridge

Ionic bond

Hydrogenbond

AP Bio

Protiens ­ Chapter 5 11

8­17­09

Aug 12­8:09 AM

Fig. 5­21g

Polypeptidechain

β Chains

HemeIron

α Chains

CollagenHemoglobin

Aug 12­8:09 AM

• 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

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Aug 12­8:09 AM

Sickle­Cell Disease: A Change in Primary Structure

• A slight change in primary structure can affect a protein’s structure and ability to function • Sickle­cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

AP Bio

Protiens ­ Chapter 5 12

8­17­09

Aug 12­8:09 AM

Fig. 5­22

PrimarystructureSecondaryand tertiarystructures

Quaternarystructure

Normalhemoglobin(top view)

PrimarystructureSecondaryand tertiarystructures

Quaternarystructure

Function

Function

β subunit

Molecules donot associatewith oneanother; eachcarries oxygen.

Red bloodcell shape

Normal red bloodcells are full ofindividualhemoglobinmoledules, eachcarrying oxygen.

10 µm

Normal hemoglobin

β

β

α

α

1 2 3 4 5 6 7Val His LeuThr Pro GluGlu

Red bloodcell shape

β subunit

Exposedhydrophobicregion

Sickle­cellhemoglobin β

α

Moleculesinteract withone another andcrystallize intoa fiber; capacityto carry oxygenis greatly reduced.

β

α

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm

Sickle­cell hemoglobin GluProThrLeuHisVal Val1 2 3 4 5 6 7

Aug 12­8:09 AM

Fig. 5­22a

PrimarystructureSecondaryand tertiarystructures

Function

Quaternarystructure

Molecules donot associatewith oneanother; eachcarries oxygen.

Normalhemoglobin(top view)

β subunit

Normal hemoglobin

7654321

β

α

α

β

GluVal

His Leu

Thr

Pro

Glu

Aug 12­8:09 AM

Fig. 5­22b

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules interact with one another andcrystallize into a fiber; capacity to carry oxygenis greatly reduced.

Sickle­cellhemoglobin

β subunit

Sickle­cell hemoglobin

7654321

β

α

α

β

Val

Val

His Leu

Thr

Pro

Glu

Exposedhydrophobicregion

AP Bio

Protiens ­ Chapter 5 13

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Aug 12­8:09 AM

Fig. 5­22c

Normal red bloodcells are full ofindividualhemoglobinmolecules, each carrying oxygen.

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm 10 µm

Aug 12­8:09 AM

What Determines Protein Structure?

• In addition to primary structure, physical and chemical conditions can affect structure• Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel• This loss of a protein’s native structure is called denaturation• A denatured protein is biologically inactive

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Aug 12­8:09 AM

Fig. 5­23

Normal protein Denatured protein

Denaturation

Renaturation

AP Bio

Protiens ­ Chapter 5 14

8­17­09

Aug 12­8:09 AM

Protein Folding in the Cell

• It is hard to predict a protein’s structure from its primary structure• Most proteins probably go through several states on their way to a stable structure• Chaperonins are protein molecules that assist the proper folding of other proteins

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings