1. Proteins

2. The 411
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
Most important, protein enzymes function as catalysts in cells, regulating metabolism by selectively accelerating chemical reactions without being consumed.

4. Amino Acids Small – molecules (20 variants)
1 Amino group
1 Carboxyl Group
1 “R” Group
Amino acids differ in their properties due to differing side chains, called R groups
Joined by Peptide Bonds to form Polypeptides
A protein consists of one or more polypeptides
Each polypeptide has a unique linear sequence of amino acids

5. Fig. 5-UN1
Alpha carbon
Amino
group
Carboxyl
group

7. How to Make Proteins!
DNA T A C C G C T C C G C C G T C G A C A A T A C C A C T
mRNA ____________________________________________________________________________
tRNA ____________________________________________________________________________
AA ____________________________________________________________________________

9. What makes all Amino Acids different?
Fig. 5-17a
Nonpolar
Glycine
(Gly or G)
Alanine
(Ala or A)
Valine
(Val or V)
Leucine
(Leu or L)
Isoleucine
(Ile or I)
Figure 5.17 The 20 amino acids of proteins
Methionine
(Met or M)
Phenylalanine
(Phe or F)
Tryptophan
(Trp or W)
Proline
(Pro or P)
What makes all Amino Acids different?

10. Polar Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C)
Fig. 5-17b
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)
Figure 5.17 The 20 amino acids of proteins

11. Electrically charged Acidic Basic Aspartic acid (Asp or D)
Fig. 5-17c
Electrically
charged
Acidic
Basic
Figure 5.17 The 20 amino acids of proteins
Aspartic acid
(Asp or D)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)

12. Polypeptide Formation
Fig. 5-18
Polypeptide Formation
Peptide
bond
(a)
Side chains
Peptide
bond
Figure 5.18 Making a polypeptide chain
Backbone
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
(b)

13. Structure
Groove
Groove

14. Levels of Structure The primary structure Secondary structure
Unique sequence of amino acids
Secondary structure
Found in most proteins, consists of coils and folds in the polypeptide chain due to Hydrogen Bonding
Tertiary structure
Determined by interactions among various side chains (R groups)
Fully Folded
Quaternary structure
Results when a protein consists of multiple polypeptide chains

15. Primary
Primary Structure 1 5
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
+H3N
Amino end 10
Amino acid
subunits 15 20 25

16. Secondary Structure Beta pleated sheet Examples of amino acid subunits
Fig. 5-21c
Secondary Structure
Beta pleated sheet
Examples of
amino acid
subunits
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
Figure 5.21 Levels of protein structure—secondary structure
alpha helix

17. Tertiary Hydrophobic interactions and van der Waals interactions
Fig. 5-21f
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Figure 5.21 Levels of protein structure—tertiary and quaternary structures
Ionic bond
Tertiary

18. Quaternary
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

19. Polypeptide  Chains chain Iron Heme  Chains Hemoglobin Collagen
Fig. 5-21g
Polypeptide
chain
 Chains
Iron
Figure 5.21 Levels of protein structure—tertiary and quaternary structures
Heme
 Chains
Hemoglobin
Collagen

20. Fig. 5-22
Normal hemoglobin
Sickle-cell hemoglobin
Primary
structure
Primary
structure
Val
His
Leu
Thr
Pro
Glu
Glu
Val
His
Leu
Thr
Pro
Val
Glu 1 2 3 4 5 6 7 1 2 3 4 5 6 7
Exposed
hydrophobic
region
Secondary
and tertiary
structures
Secondary
and tertiary
structures
 subunit
 subunit    
Quaternary
structure
Normal
hemoglobin
(top view)
Quaternary
structure
Sickle-cell
hemoglobin    
Function
Molecules do
not associate
with one
another; each
carries oxygen.
Function
Molecules
interact with
one another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
Figure 5.22 A single amino acid substitution in a protein causes sickle-cell disease
10 µm
10 µm
Red blood
cell shape
Normal red blood
cells are full of
individual
hemoglobin
moledules, each
carrying oxygen.
Red blood
cell shape
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.