Polvi lec #15 Flashcards
What is the structure of cilia and flagella?
cilia/flagella is covered in a membrane that is continuous with the cell’s plasma membrane, is has a microtubule organizing center called a basal body which organizes the axoneme.
How are microtubules organized in cilia and flagella?
The microtubules are oriented so the negative end is near the basal body and the positive end is near the distal end
How does cilia and flagella move?
The dynein stalks connected to the A tubule do a power stroke (confirmational change upon ATP hydrolysis) this causes the stalk to detach from A tubule and reattach which moves A tubule to the negative end.
What is axoneme? What is it’s structure?
axoneme is a core is that contains microtubules in the cilia and flagella, is organized by the basal body, and has 9 outside doublet tubules with two tubules inside. The doublets are connected to each other via nexin. And in the doublet microtubules, dynein tails are anchored to the A tubule in each pair and dynein stalks to the B tubule.
What limits the amount cillia and flagella’s microtubules move?
Nexin
What are the three things the cytoskeleton is composed of?
intermediate filaments
microtubules
actin
What do actin filaments do for the cell?
They help with cell motility (cytokinesis, movement of vesicles, phagocytosis) and provide structural support (help with the shape of cells and help with support for cellular projections)
What is the structure of actin filaments? What are the charges of it’s ends, what is it composed of, what’s the shape?
actin filaments have a barbed positive end and a negative pointed end, this is due to the individual G-actin monomers which are added to the filament in an orientation to create this, the filament is a parallel double stranded helix
What are the motor proteins for actin called?
myosin
How are actin filaments assembled?
ATP-actin is put into filament, then actin converts ATP to ADP, atp-actin is added to both the barbed and pointy ends, when the concentration of the available actin begins to drop the pointed end stops growing first and ADP-actin disassociates as there’s no more ATP-actin, however the barbed end continues to grow so the filament now stays in a steady state (treadmilling- it’s growing and shrinking at same time)
What is treadmilling?
the individual actin monomers fall off the minus end and get added to the plus end, so monomers move from plus to minus end but the length of the filament stays the same
Why does the pointed end stop growing when the conc of available actin falls but the barbed end continues to grow?
Because the critical concentration- which is the minimum amount needed for the pointed end to grow is higher than that of the barbed end.
What is Myosin type 2? What is it’s structure?
Is the convential type, it is the type of myosin involved is muscle contraction, it has a motor head (which binds to the actin filament, hydrolyzes atp, conserves it’s amino acid sequence), it has a neck(which moves during the power stroke and detaches head), and it has a tail (is made up of two heavy chains and allows the filaments of myosin to form)
To what side of the actin filament do myosin move?
all myosin (except type 6) move towards the positive barbed end
Is myosin type 5 convential or unconventional? How does it move?
myosin type 5 moves along actin filaments and moves in a hand over hand movement with it’s long necks swinging and creating the power stroke
