1. Protein Structure

2. Proteins have many structures, resulting in a wide range of functions
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

3. Table 5-1

4. Polypeptides
Polypeptides are polymers built from the same set of 20 amino acids
A protein consists of one or more polypeptides

5. Protein Structure and Function
A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape

6. Protein Structure and Function
The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s structure determines its function

7. Protein Structure and Function
The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s structure determines its function
Four Levels of Protein Structure

8. Primary Structure
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
A polypeptide containing 50 or more amino acids is called a protein.

9. Primary Structure
The primary structure of a protein is the sequence of amino acids in the peptide chain.
Ala – Leu – Cys - Met

10. Primary Structure
The nonapeptides oxytocin and vasopressin have similar primary structures.
Only the amino acids at positions 3 and 8 differ.

11. +H3N Primary Structure Amino end Amino acid subunits 1 5 10 15 20 25
Carboxyl end
125
120
115
110
105
100 95 90 85 80 75 20 25 15 10 5 1
Amino acid
subunits
+H3N
Amino end 25 20 15 10 5 1
Primary Structure

12. Insulin
Was the first protein to have its primary structure determined.
Of humans has a primary structure that is similar to the insulin of pigs and cows.

13. Secondary Structure: Alpha Helix
The secondary structures of proteins indicate the arrangement of the polypeptide chains in space.
The alpha helix is a three-dimensional arrangement of the polypeptide chain that gives a corkscrew shape like a coiled telephone cord.

14. Alpha Helix
The coiled shape of the alpha helix is held in place by hydrogen bonds between the amide groups and the carbonyl groups of the a.as. along the chain.

15. Secondary Structure: Pleated Sheet
Holds proteins in a parallel arrangement with hydrogen bonds.
Has R groups that extend above and below the sheet.
Is typical of fibrous proteins such as silk.

16. Secondary Structure: Triple Helix
Consists of three alpha helix chains.
Contains large amounts glycine, proline, hydroxy proline and hydroxylysine that contain –OH groups for hydrogen bonding.
Is found in collagen, connective tissue, skin, tendons, and cartilage.

17. Fibrous Proteins
Consist of long, fiber-like shapes.
Such as alpha keratins make up hair, wool, skin, and nails.
Such as feathers contain beta keratins with large amounts of beta-pleated sheet structures.

18. Have compact, spherical shapes.
Globular Proteins
Have compact, spherical shapes.
Carry out synthesis, transport, and metabolism in the cells.
Like Myoglobin store and transport oxygen in muscle.
Myoglobin

19. Gives a specific overall shape to a protein.
Tertiary Structure
Gives a specific overall shape to a protein.
Involves interactions and cross links between different parts of the peptide chain.
Is stabilized by
Hydrophobic and hydrophilic interactions
Salt bridges ( Ionic bond)
Hydrogen bonds
Disulfide bonds

20. Tertiary Structure

21. Hydrophobic interactions and van der Waals interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond

22. Tertiary Structure
The interactions of the R groups give a protein its specific three-dimensional tertiary structure.

23. Quaternary Structure
The quaternary structure contains two or more tertiary subunits.
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
The heme group in each subunit picks up oxygen for transport in the blood to the tissues.

24. Tertiary Structure
Quaternary Structure

26. Summary of Structural Levels

28. Sickle-Cell Disease: A Change in Primary Structure
A slight change in primary structure can affect a protein’s structure and ability to function
Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

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

30. 10 µm
10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.

31. Protein Hydrolysis
Splits the peptide bonds to give smaller peptides and amino acids.
Occurs in the digestion of proteins.
Occurs in cells when amino acids are needed to synthesize new proteins and repair tissues.

32. Hydrolysis of a Dipeptide
In the lab, the hydrolysis of a peptide requires acid or base, water and heat.
In the body, enzymes catalyze the hydrolysis of proteins.

33. Denaturation
Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
This loss of a protein’s native structure is called denaturation.
A denatured protein is biologically inactive

34. Denaturation
Denaturation involves the disruption of bonds in the secondary, tertiary and quaternary protein structures.
Heat and organic compounds break apart H bonds and disrupt hydrophobic interactions.
Acids and bases break H bonds between polar R groups and disrupt ionic bonds.
Heavy metal ions react with S-S bonds to form solids.

35. Applications of Denaturation
Denaturation of protein occurs when:
An egg is cooked.
The skin is wiped with alcohol.
Heat is used to cauterize blood vessels.
Instruments are sterilized in autoclaves.