Ch29 Amino Acids, Polypeptides and Proteins

8/14/2019 Ch29 Amino Acids, Polypeptides and Proteins

1/62

1

Amino Acids, Polypeptides,and Proteins

Chapter 29

Hein * Best * Pattison * Arena

Colleen Kelley

Chemistry DepartmentPima Community College

John Wiley and Sons, Inc.

Version 1.0


2/62

2

Chapter Outline

29.1 The Structure-

Function Connection

29.2 The Nature of AminoAcids

29.3 Essential Amino Acids

29.4 D-Amino and L-Amino

Acids

29.5 Amphoterism

29.6 Formation of

Polypeptides

29.7 Protein Structure

29.8 Some Examples of Proteins

and Their Structure

29.9 Loss of Protein Structure

29.10 Tests for Proteins and

Amino Acids

29.11 Determination of the

Primary Structure of Polypeptides

29.12 Synthesis of Peptides and

Proteins


3/62

3

The Structure-FunctionConnection


4/62

4

Proteins function as structural materials

and as enzymes (catalysts) that regulate the

countless chemical reactions taking placein every living organism.

All proteins are polymeric substances

that yield amino acids on hydrolysis.

Those which yield only amino acids when

hydrolyzed are classified as simple proteins.

Those which yield amino acids and one or

more additional products are classified as

conjugated proteins.


5/62

5

Proteins are highly specific in their

functions.

The sequence of amino acids in a

protein establishes the function of thatprotein.

Full understanding of the function of a

protein requires an understanding of itsstructure.


6/62

6

The Nature of

Amino Acids


7/62

7

Each amino acid has two functional

groups: an amino group (-NH2) and acarboxyl group (-COOH).

H3

C CH C

NH 2

OH

O

alanine

carboxyl group

amino group


8/62

8

Amino acids as a whole are represented

by this general formula:

R CH C

NH 2

OH

O

The portion of the molecule designated as Ris

commonly referred to as the amino acid side chain.


9/62

9

The side chain (-R) may contain:

1. Alkyl groups2. Aromatic groups

3. Amino groups

4. Carboxyl groups

5. Hydroxyl groups

6. Sulfur-containing groups

Amino acids can be divided into

three groups depending on the natureof theR group.


10/62

10


11/62


12/62


13/62

13


14/62

14


15/62


16/62

16

Essential amino acids are essential to

the normal functioning of the human

body.

Since the body is not capable ofsynthesizing them, they must be

supplied in our diets.


17/62

17


18/62


19/62

19

D-Amino Acids andL-Amino Acids


20/62

20

All amino acids, except glycine, have at

least one asymmetric carbon atom.

NH 2C

COOH

CH 3

H HC

COOH

CH 3

H2N

D-(-)-alanine L-(+)-alanine


21/62


22/62

22

Amphoterism

Amino acids are amphoteric when theycan react either as an acid or a base.

H3C CH C

NH 2

OH

O

+ NaOH H3C CH C

NH 2

O-

Na+

O

+ H2O

H3C CH C

NH 2

OH

O

+ HCl H3C CH C

NH 3+

Cl-

OH

O


23/62


24/62


25/62


26/62

26

Formation ofPolypeptides


27/62

27

Proteins are polyamides consisting of amino

acid units joined through amide structures.

Two amino acids can combine and

lose a molecule of water to form a

peptide bond or peptide linkage.

H2N CH C

CH 3

OH

O

H2N CH C

H

OH

O

+

H2N CH C

CH 3

O

HN CH C

H

OH

O

+ H2O

peptide bond

alanine glycine

Ala-Gly


28/62


29/62


30/62


31/62


32/62

32

The amino acid sequenceand chain length give a

polypeptide its biologicaleffectiveness and specificity.


33/62


34/62

34


35/62

35

Protein Structure


36/62


37/62

37

The primary structure of a protein is

established by the number, kind, and sequence

of amino acid units composing the polypeptidechain or chains making up the molecule.

The primary structure determines the alignment

of side-chain characteristics, which, in turn,determines the three-dimensional shape into

which the protein folds.

In this sense, the amino acid sequence is ofprimary importance in establishing protein

shape.


38/62

38

Figure 29.2 Amino acid sequence of beef insulin


39/62

39

The secondary structure of proteins can

be characterized as a regular three-dimensional structure held together by

hydrogen bonding between the oxygen

of the C=O and the hydrogen of the H-Ngroups in the polypeptide chains.

The a-helical and b-pleated-sheet

structures are two examples ofsecondary structure.


40/62


41/62

41


42/62


43/62

43

A quaternary structure is found in somecomplex proteins.

These proteins are made of two or moresmaller protein subunits (polypeptidechains).

The quaternary structure refers to the shapeof the entire complex molecule and isdetermined by the way in which thesubunits are held together by noncovalent

bondsthat is, hydrogen bonding, ionicbonding, and so on.


44/62

44

Some Examples

of Proteins and

Their Structure


45/62

45

Fibrous Proteins

The fibrous proteins contain a highlydeveloped secondary structure.

These proteins tend to function in

support roles.

The most abundant protein in theanimal kingdom, collagen, is a fibrous

protein with a unique secondarystructure.


46/62

46

Figure 29.3 A fibrous protein.


47/62

47

Figure 29.3

Fibrous

proteins.


48/62


49/62

49

Globular Proteins

Myoglobina binding protein

Carboxypeptidase Aan enzyme

Immunoglobulin Ga binding protein

Hemoglobina binding protein


50/62


51/62

51

Figure 29. 5 Representations of carboxypeptidase A. This

is a small enzyme that catalyzes protein digestion in the

small intestine.


52/62


53/62

53

Figure 29.7 Diagrammatic shape of a typical

immunoglobulin G protein.


54/62

54

Figure 29.8 Representations of hemoglobin. In the

spacefilling model, just the edges of the heme groups

(shown in blue) are visible in the two closest subunits.


55/62

55

Figure 29.8 The oxygen-hemoglobin binding process


56/62


57/62

57

If a protein loses only its natural three-dimensional conformation, the processis referred to as denaturation.

Denaturation involves the alteration ordisruption of the secondary, tertiary, orquaternarybut not primary- structureof proteins.

Because a proteins function depends

on its natural conformation, biologicalactivity is lost with denaturation.


58/62

58

Figure 29.11 Structural change when a protein molecule is denatured:

The relatively weak hydrogen, electrostatic, and disulfide bonds are

broken resulting in a change of structure and properties (.denotes the

noncovalent bonds that stabilize a proteins natural conformation)


59/62

59

Loss of protein structure alsooccurs with hydrolysis of thepeptide bonds to produce free

amino acids. This chemical reaction destroys

the proteins primary sequence.


60/62

60

Tests for Proteins

and Amino Acids


61/62


62/62

Ch29 Amino Acids, Polypeptides and Proteins

Documents

Transcript of Ch29 Amino Acids, Polypeptides and Proteins