Lecture 8 Flashcards
What are three types of filaments?
Actin, microtubules and intermediate filaments
What is the cytoskeleton responsible for?
Subcellular organization, structural integrity and movement of the cell
What is the structure of actin?
Twisted 2 strand structure 9-9nm in diameter
What is the structure of intermediate filaments?
Rope like structure - 10nm in diameter
What is the structure of microtubules?
Hollow tubes 24nm in diameter
What is the most abundant intracellular protein?
Actin
How many forms of actin are there?
Human genome encodes for 6 isoforms of acting
- four alpha actins in muscle
- B- and y-actin in non-muscle cells
What is a 42kDA ATPase?
Actin
What is G-Actin?
globular, monomeric actin
What is F-Actin?
Filament actin polymer, has structural and functional polarity, thin flexible filament
What is important to maintain a high concentration of monomeric actin in the cell?
Sequestering proteins
What are severing proteins?
Break actin filaments, necessary to breakdown existing networks
What are capping proteins ?
Cap the (+) or (-) end and stabilize the filament at that end
What are branching proteins?
Binds to an actin filament and initiates the formation of daughter filaments
What is the responsibility of the small protein fimbrin?
cross-linked filaments into bundles
What protein cross-links F-actin into networks
Filamin protein
What does the actin network at the cell cortex do?
Stabilizes the plasma membrane
What is the roles of having a dynamic cortex?
actin assembly and disassembly
What stabilizes actin filament in sarcomere of skeletal muscle?
Capping proteins
What are 3 roles of actin networks?
Shape, move and divide cells
What changes shape during blood clotting?
Platelets
What occurs during activation of platelets?
Results in reorganization of actin network, which causes a dramatic change in cell shape
What end of the actin filaments are oriented with the (+) end?
towards the plasma membrane
How do actin filaments grow?
They grow by addition of G-actin to the (+) end
What forms new actin branches?
Arp 2/3 complex
What stabilizes filaments?
capping protein
What end to the actin filaments disassemble
on the (-) end at a distance from the cell surface
What does the optical trap measure?
The force generated by a single myosin
Describe what happens in a optical trap?
- A laser beam traps the latex bead in the center of the focus and holds the beam in position
- The strength of the trap is regulated by the intensity of the laser beam
- The beam intensity is increased until the myosin motor is unable to move the bead
Describe muscle cells
large, tubular cells with many nuclei
What causes the contraction of muscle cells?
myosin 2 motors moving along actin
What does myosin 2 require?
ATP
Both tubulins are —–
GTP binding proteins
Alpha tubulin binds tightly to GTP and does not ———
hydrolyze the nucleotide
Beta tubulin hydrolysis and exchanges the ———
the bound nucleotide
What is bound to GTP and what is bound to GDP.
alpha tubulin is bound to GTP
beta tubulin is GDP bound
What is the microtubule structure?
Hollow tubes made of protofilaments
What are protofilaments made of?
made of tubulin dimers
Doe microtubules have polarity
yes
What is more ridged, microtubules or actin filaments?
microtubules
What stabilizes the MT ends of a microtubules?
GTP cap
