1. Proteins

2. Proteins R O | H || —C— C—OH N H Monomer: Amino Acid
Atoms: carbon, hydrogen, oxygen, nitrogen
amino = NH2
acid = COOH
Monomer: Amino Acid R
C—OH || O |
—C— H N H
*20 Different types of amino acids

3. Nonpolar side chains; hydrophobic )
Glycine
(Gly or G)
Alanine
(Ala or A)
Valine
(Val or V)
Leucine
(Leu or L)
Isoleucine
(le or )
Figure 3.17a The 20 amino acids of proteins (part 1: nonpolar)
Methionine
(Met or M)
Phenylalanine
(Phe or F)
Tryptophan
(Trp or W)
Proline
(Pro or P) 3

4. Polar side chains; hydrophilic
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Figure 3.17b The 20 amino acids of proteins (part 2: polar)
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamine
(Gln or Q) 4

5. Electrically charged side chains; hydrophilic
Basic (positively charged)
Acidic (negatively charged)
Figure 3.17c The 20 amino acids of proteins (part 3: charged)
Aspartic acid
(Asp or D)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H) 5

6. Monomer: Polypeptide
enzyme

7. Side chains Back- bone Peptide bond Amino end (N-terminus)
Figure 3.18b Making a polypeptide chain (part 2: new peptide bond)
Peptide
bond
Amino end
(N-terminus)
Carboxyl end
(C-terminus) 7

8. Proteins Most structurally & functionally diverse group
Function: involved in almost everything that goes on in a living thing! (50% dry mass of cells
enzymes (pepsin, DNA polymerase)
structure (keratin, collagen)
carriers & transport (hemoglobin, aquaporin)
cell communication
signals (insulin & other hormones)
receptors
defense (antibodies)
movement (actin & myosin)
storage (bean seed proteins)
Storage: beans (seed proteins)
Movement: muscle fibers
Cell surface proteins: labels that ID cell as self vs. foreign
Antibodies: recognize the labels
ENZYMES!!!!

11. Protein models Protein structure visualized by X-ray crystallography
extrapolating from amino acid sequence
computer modelling
lysozyme

12. Protein Structure and Functions
*Each protein is made up of one or more polypeptide chains twisted, folded and coiled into a unique shape *4 Levels to protein structure

13. Primary Structure
Sequence (order) of amino acids in chain *This order is determined by DNA instructions *Even just one amino acid change can make a big difference

14. Hydrophilic! Hydrophobic! Secondary and Tertiary Structures Primary
Quaternary
Structure
Red Blood Cell
Shape
Function
Normal
hemoglobin
Molecules do not
associate with one
another; each carries
oxygen. 1 2 3 4
Normal  5
 subunit  6  7
5 m 
Hydrophilic!
Exposed hydro-
phobic region
Sickle-cell
hemoglobin
Molecules crystallized
into a fiber; capacity to
carry oxygen is reduced. 1 2
Figure 3.22 A single amino acid substitution in a protein causes sickle-cell disease. 3
Sickle-cell 4  5  6
 subunit  7 
5 m
Hydrophobic! 14

15. Secondary Structures
Coils and folds called Alpha Helix and Beta pleated sheets caused by hydrogen bonding between polypeptide backbones

16. Tertiary Structure
Three dimensional shape caused by “weak” interactions between the side chains
Hydrophobic
interactions and
van der Waals
interactions
Hydrogen
bond
Disulfide
bridge
Ionic bond
Figure 3.21d Exploring levels of protein structure (part 8: tertiary stabilization)
Polypeptide
backbone 16

17. Quaternary Structure
The overall structure formed by two or more polypeptides This is when protein becomes functional Caused by hydrophobic interatctions
hemoglobin
collagen = skin & tendons

18. Protein structure (review)
R groups
hydrophobic interactions
disulfide bridges
(H & ionic bonds) 3°
multiple polypeptides
hydrophobic interactions 1°
sequence determines structure and…
structure determines function.
Change the sequence & that changes the structure which changes the function.
amino acid sequence
peptide bonds 4° 2°
determined by DNA
R groups
H bonds

19. Chaperonins assist in proper folding of proteins

20. Protein denaturation Denaturation is the unfolding of a protein
Conditions that disrupt H bonds, ionic bonds, disulfide bridges
*Temperature
*pH
*salinity
Result in changes in secondary and
tertiary structures
Wrong shape = no function