1. Proteins
Proteins have many structures, resulting in a wide range of functions
Proteins do most of the work in cells and act as enzymes
2. Proteins are made of monomers called amino acids

2. An overview of protein functions
Table 5.1

3. Enzymes
3. Are a type of protein that acts as a catalyst, speeding up chemical reactions
Substrate
(sucrose)
Enzyme
(sucrase)
Glucose OH
H O
H2O
Fructose
3 Substrate is converted
to products.
1 Active site is available for
a molecule of substrate, the
reactant on which the enzyme acts.
Substrate binds to
enzyme. 2
4 Products are released.
Figure 5.16

4. Polypeptides 4. Polypeptides are polymers (chains) of amino acids
A protein consists of multiple amino acids connected by peptide bonds

5. Amino acids
Are organic molecules possessing both carboxyl and amino groups
Differ in their properties due to differing side chains, called R groups

6. Twenty Amino Acids 20 different amino acids make up proteinsH
H3N+ C
CH3 CH
CH2 NH
H2C
H2N
Nonpolar
Glycine (Gly)
Alanine (Ala)
Valine (Val)
Leucine (Leu)
Isoleucine (Ile)
Methionine (Met)
Phenylalanine (Phe)
Tryptophan (Trp)
Proline (Pro)
H3C
Figure 5.17 S
20 different amino acids make up proteins

7. Polar Electrically chargedOH
CH2 C H
H3N+ O
CH3 CH SH
NH2
Polar
Electrically
charged –O
NH3+
NH2+
NH+ NH
Serine (Ser)
Threonine (Thr)
Cysteine
(Cys)
Tyrosine
(Tyr)
Asparagine
(Asn)
Glutamine
(Gln)
Acidic
Basic
Aspartic acid
(Asp)
Glutamic acid
(Glu)
Lysine (Lys)
Arginine (Arg)
Histidine (His)

8. Amino Acid Polymers
5. Amino acids are linked by peptide bonds

9. Protein Conformation and Function
6. A protein’s specific conformation (shape) determines how it functions

10. Four Levels of Protein Structure
Primary structure
Is the unique sequence of amino acids in a polypeptide
Figure 5.20 –
Amino acid subunits
+H3N Amino end o
Carboxyl end c
Gly
Pro
Thr
Glu
Seu
Lys
Cys
Leu
Met
Val
Asp
Ala
Arg
Ser
lle
Phe
His
Asn
Tyr
Trp
Lle

11. Secondary structure
Is the folding or coiling of the polypeptide into a repeating configuration
Includes the  helix and the  pleated sheet O C
 helix
 pleated sheet
Amino acid subunits N H R H
Figure 5.20

12. Is the overall three-dimensional shape of a polypeptide
Tertiary structure
Is the overall three-dimensional shape of a polypeptide
Results from interactions between amino acids and R groups
CH2 CH
O H O C HO
NH3+ -O S
CH3
H3C
Hydrophobic interactions and van der Waals interactions
Polypeptide backbone
Hyrdogen bond
Ionic bond
Disulfide bridge

13. Quaternary structure
overall protein structure that results from the combination of two or more polypeptide subunits
Polypeptide chain
Collagen
 Chains
 Chains
Hemoglobin
Iron
Heme

14. Review of Protein Structure
+H3N
Amino end
Amino acid
subunits
helix

15. Sickle-Cell Disease: A Simple Change in Primary Structure
Results from a single amino acid substitution in the protein hemoglobin

16. Sickle-cell hemoglobin
Primary structure
Secondary and tertiary structures
Quaternary structure
Function
Red blood cell shape
Hemoglobin A
Molecules do not associate with one another, each carries oxygen.
Normal cells are full of individual hemoglobin molecules, each carrying oxygen  
10 m
Hemoglobin S
Molecules interact with one another to crystallize into a fiber, capacity to carry oxygen is greatly reduced.
 subunit 1 2 3 4 5 6 7
Normal hemoglobin
Sickle-cell hemoglobin
. . .
Figure 5.21
Exposed hydrophobic region
Val
Thr
His
Leu
Pro
Glul
Glu
Fibers of abnormal hemoglobin deform cell into sickle shape.

17. What Determines Protein Conformation?
Protein conformation Depends on the physical and chemical conditions of the protein’s environment
Temperature, pH, salinity, etc. affect protein structure

18. Denaturation is when a protein unravels and loses its native conformation (shape)
Renaturation
Denatured protein
Normal protein
Figure 5.22

19. The Protein-Folding Problem
Most proteins
Probably go through several intermediate states on their way to a stable conformation
Denaturated proteins no longer work in their unfolded condition
Proteins may be denaturated by extreme changes in pH or temperature

20. Chaperonins
Are protein molecules that assist in the proper folding of other proteins
Hollow cylinder
Cap
Chaperonin (fully assembled)
Steps of Chaperonin Action: An unfolded poly- peptide enters the cylinder from one end.
The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide.
The cap comes off, and the properly folded protein is released.
Correctly folded protein
Polypeptide 2 1 3
Figure 5.23