1. Cytoskeletal Structural Proteins
Polypeptide types:
Actin a microfilaments (70 Å diameter),
Keratin an intermediate filament (100 Å diameter)
Tubulin a microtubule (240 Å diameter)

2. Actin Microfilament Assembly
F-actin (filamentous) and G-actin (globular)
Polarity with ATP-binding end the negative (-) end
Greater addition on the positive (+) end
Single subunit

3. Microfilament Treadmilling

4. Crawling Cells via Microfilament Treadmilling
Highly Dense Leading edge
Upturned Leading edge

5. Cytoskeletal Structural Proteins
Polypeptide types:
Actin a microfilaments (70 Å diameter),
Keratin an intermediate filament (100 Å diameter)
Tubulin a microtubule (240 Å diameter)

6. Intermediate Filaments
Basic structural unit: dimer of α-helices that wind around each other – coiled coil
Includes soft keratins that define internal structures and hard keratins of skin,
hair and claws
Exclusively structural
proteins
Dead epidermal skin cells mostly keratin

7. Residue Arrangement in a Coiled Coil Structure
Seven amino acid pseudo repeat with positions 1 and 4 hydrophobic residues
Hydrophobic strip along the side of the helix

8. Intermediate Filament Dimer Model
Human hair

9. Special Intermediate Filament for Large Animals: Collagen
Triple helix extracellular matrix
Holds cells, organs and bones together
Rich in Gly (30%), Pro (30%)
and hydroxyproline (30%)

10. Collagen Triple Helix Cross Section
A narrow left-handed single helix but
A right-handed triple helix

11. Collagen Single and Triple Helix Structure
Pro drives the left handed configuration
Only Gly can fit in the center position
Reverse winding strengthens the helix

12. Lys Side Chain Cross Linking
Collagen stronger than steel on a per weight basis

13. Cytoskeletal Structural Proteins
Polypeptide types:
Actin a microfilaments (70 Å diameter),
Keratin an intermediate filament (100 Å diameter)
Tubulin a microtubule (240 Å diameter)

14. Tubulin Forms Hollow Microtubules
Tubular structure provides greater strength

15. β-Tubulin and Tubulin Dimer
Describe the secondary structures of beta-tubulin.
Guanosine nucleotide-sites
with α-subunit site solvent inaccessible

16. Microtubules Function in Cell Division
Draws chromosomes apart before cell division
Polar structure
that grows more
rapidly at the (+)
end
Microtubule
treadmilling
can occur

17. Drug-Mediated Microtubule Depolymerization
Colchicine binds between the alpha and beta subunits

18. Drug-Mediated Microtubule Polymerization
Taxol stabilizes beta-tubulin subunits preventing depolymerization
Blocks rapidly dividing cells such as tumor cells

19. Motor Protein Thick Filament
Actin interacts with the thick filament of myosin causing muscle contraction
Thick
Filament

20. Myosin Head and Neck Region

21. Binding of ATP to Myosin Releases Myosin from Actin

22. ATP Hydrolysis Causes a myosin conformational shift and
Increases myosin binding to actin
Myosin binds to actin farther along
the thin filament

23. Power Stroke
Myosin binding to actin causes a release of phosphate and ADP

24. Chapter 5 Problems:
1, 3, 5, 7, 9, 11, 13, and 17, 20, 25, 51