Final Topic 22 - Eukaryotes - Cytoskeleton Part 2 Flashcards
Found in all eucaryotic cells
Actin Filaments
Actin Filaments form:
1) Microvilli of intestinal epithelial cells
2) Small contractile bundles in cells
3) Dynamic protrusions of the motile cells
4) Contractile ring to separate cells during cell division
Formed by polymerization of monomers
Actin Filaments
2 filaments of actin monomers all of which point in the same direction
Twist around each other
G-actin
Monomer
Globular Actin
F-actin
Actin Filament
Actin has
polarity
(+) end
addition
(-) end
Loss
Actin can bind and hydrolyze
ATP
ATP bound actin has a higher affinity to
Form a filament
ADP-actin is more like to
Disassemble
Promotes disassembly
Nucleotide hydrolysis
Actin-ATP adds to ____ end and Actin-ADP then falls off the _____ end
(+)
-
About half of actin in the cell is maintained as
G-actin
Protein that binds to the G-actin monomer to keep it from polymerizing into F-actin
Profilin
Regulates when and where the cell can make a filament
Profilin
Actin polymerizes at
The (+) end
Actin depolymerizes at
The (-) end
Three main actin structures that cells use to move
1) Filopodium
2) Lamellipodium
3) Contractile bundles - actin and Myosin II (motor protein)
Allow cells to move
Actin filaments
Steps of cell locomotion
- Actin polymerization at the lamellipodium pushes cell forward
- The cell attaches the lamellipodium to the substrate through feet called integrins
- Actin and Myosin II (actin motor protein) provide contractile forces to pull the cell forward
Cell “feet”
Integrins
Protein that binds to the (+) end of F-actin and promotes the addition of G-actin to the end of an unbranched filament
Formins
Bind to the side of an existing actin filament and nucleate actin branching
ARP 2/3 Complex
A family of actin-dependent motor proteins
Myosin
Myosin bind and hydrolyze
ATP
Myosin moves towards the
(+) end of the filament
Has one actin binding ATPase head and one tail
Myosin I
The main myosin protein in muscle
Myosin II
Forms a dimer
Myosin II
Two actin binding ATPase heads joined together by a coiled-coil tail
Myosin II
Myosin II molecules cluster together through their tails into
Myosin Bipolar Filaments
Muscle tissue is made up of
Muscle cells
Multi-nucleated cells with cytoplasm of myofibrils
Muscle cells
Cylindrical tubes that consist of repeating contractile units called sarcomeres
Myofibrils
The basic contractile unit of the muscle
Sarcomere
Actin filaments are anchored to the _________ at their _______ ends
Z disc
(+) ends
The actin filaments face
Each other in the sarcomere
Upon contraction, the myosin heads move
Towards the (+) end and pulls the actin filaments towards each other
Myosin II Power Stroke
- Myosin head is bound in nucleotide free form to actin
- ATP binds to myosin and releases it from actin
- Hydrolysis of myosin head changes the conformation of the head forward
- Binding of the head to actin releases Pi
- Release of ADP provides the conformational change to move the head backwards
The use of ATP hydrolysis to move along the actin filament
Myosin head power stroke
