1. 1. Storage: plant/animal starch
Polysaccharides:
1. Storage: plant/animal starch
‘energy reserves’
- liver
- muscles
2. Structural:
cellulose
chitin

2. Polysaccharides – It’s all in the linkage!
Fig 5.7

3. Polysaccharides Structural polysaccharide - cellulose
Hydrogen bonds between
hydroxyls on C3 and C6
Food for thought…

4. Storage Polysaccharides - Summary
Storage polysaccharide – starch (linear chains of repeating α glucose units)
Plant starch
Animal starch
branched: (α 1-6) amylopectin
or unbranched amylose
always branched (α 1-6) glycogen
length and location of branches is random
Why store as a polymer?
How are such stores tapped?
Why don’t proteins branch?

5. Tapping Glycogen Reserves
What happens to
glucose now?

7. Proteins Amino Acid Workhorse molecules of the cell
Polymers formed as a result of dehydration synthesis reactions that link together the amino acid monomers…
Amino Acid
Each of the amino acids has different
chemical properties based on its ‘R’ group α

8. The Nonpolar Amino Acids+ -
zwitterion – can act as acid or base
in the cell
The Nonpolar Amino Acids

9. The Polar Amino Acids
Polar, Uncharged
Polar, Charged

10. Building a linear chain of amino acids
Formation of a Protein
Building a linear chain of amino acids
Dehydration synthesis reactions
link together amino acids.
- Each amino acid is linked
to the next by a covalent
linkage called a peptide-bond
- The ends of the peptide molecule
are different:
NH2 (end) terminal
COOH (end) terminal
Proteins synthesized from N C

11. NCC – NCC – NCC- NCC - NCC Formation of a Protein - continued
Terms to note: peptide bonds
side chains
peptide ‘backbone’
imino groups
carbonyl groups
NCC – NCC – NCC- NCC - NCC

12. Formation of a Protein - Summary
Formation of Peptide Bond
Polypeptide Chain:
Figure: 3.9a-c
Caption:
(a) When the carboxyl group on one amino acid reacts with the amino group on a second amino acid, a peptide bond forms.  (b) Amino acids can be linked into long chains by peptide bonds.  (c) The sequence of amino acids in a polypeptide chain is numbered from the N-terminus (or amino-terminus) to the C-terminus (or carboxy-terminus).
Numbering System:
From: Biological Science, by S. Freeman

13. Most Peptide Bonds in the ‘Trans’ Orientation

14. From: Molecular Biology of the Cell, 5th ed. Lodish et al.

15. The Four Different Levels Used to Describe the Structure of a Protein:
Primary structure
order of amino acids from the N terminus to the C terminus
tremendous range in the size of proteins (toxins to titin)
determines the shape/conformation of the protein
Therefore, the function!
Frederick Sanger first sequenced proteins in 1953 (Nobel, 1958)
What determines 1º structure?

16. Linus Pauling Determined the structure of hemoglobin
Discovered how abnormal hemoglobin causes sickle-cell disease
Discovered α-helix and β-pleated sheets
Won the Nobel Prize for Chemistry (1954)
Won Nobel Peace Prize (1963)
The only person to win two solo prizes

18. Secondary Structure
Predictable, repeatable folding (2 types: α helix, β sheet)
Forms as a result of hydrogen bonds between the imino and the carbonyl
groups along the peptide backbone.
Linus Pauling & Robert Corey!
α helix
structually the same
between proteins
3.6 AA per turn
Every 4th AA in close prox.
Bonds are parallel to axis
always intramolecular
β (pleated) sheet
intra or intermolecular
bonds are perpendicular to
the plane of the sheet
parallel or antiparallel
From: Biological Science, by S. Freeman

19. Globular and Fibrous Proteins
Fibrous proteins have extensive 2º structure throughout length
keratins (α-helices)
Globular proteins – folded into compact
rather than filamentous forms
fibroin (silk protein – β sheets)

20. Proteins can consist of α-helices and β-pleated sheets
α-helices, β-pleated sheets and regions of neither – random coils (green)

21. Tertiary Structure
Most polypeptide chains bend and fold back upon themselves (random coils)
to produce unique, complex three dimensional shapes = conformation
Not repetitive (unlimited possibilities), not predictable (yet…)
Lowest free energy state of the protein in its environment
Involves:
hydrogen bonds between
polar amino acids
electrostatic interactions
(charged amino acids)
hydrophobic interactions
(nonpolar amino acids)
disulfide bonds

22. Quaternary (4º) Structure: multimeric proteins
Figure 3-6
Quaternary (4º) Structure:
multimeric proteins
> 1 polypeptide chain
neuraminidase – homotetramer
hemoglobin – heterotetramer (2α chains, 2β chains)

23. Quaternary (4º) Structure
What kinds of chemical interactions stabilize the association of the subunits?

24. Protein Structure - Summary
An astounding number of different proteins are possible!!!
20n
where, 20 = the number of amino acids (AA) used in protein synthesis
n = the length of the polypeptide chain (the total # of AA)
Example: how many different proteins (i.e. sequence combinations) are possible for
a polypeptide chain that contains 50 amino acids?
2050 = 2 x 1051 different sequences!!!