Lecture 10: Protein Function- Molecular Motors

list two classes of molecular motors

actin motors and microtubule motors

important representatives for actin motors

myosin and actin

important representatives for microtubule motors

kinesin and dynein

which motor is the prototype of motors and mediates muscle contraction?

actin motors

anterograde movement

kinesin

retrograde movement

dynein

how many subunits does myosin contain?

6 subunits - 2 heavy chains and 4 light chains

what does F actin consist of?

a filamentous polymer composed of G-actin monomers.

specifically, consists of 2 helical aggregates of G actin that are twisted around each other

what are the components of thick filaments?

myosin head and tail

head: contains ATPases that generate force

tail: 150nm

what are the components of thin filaments?

actin, troponin, tropomyosin

where thin filaments are held together by alpha-actinin, desmin, vimentin

Z disk

where adjacent thick filaments are joined tail to tail

M line

regions with thin filaments but no thick filaments

I band

four distinct steps that lead to force generation and muscle contraction

1. ATP binds to myosin head, causing dissociation from actin

2. as tightly bound ATP is hydrolyzed to ADP and Pi, a conformational change occurs

3. Myosin head attaches to actin filament, causing release of Pi

4. Pi release triggers "power stroke" which is a conformational change in the myosin head that moves both actin and myosin filaments relative to one another. ADP is released in the process

how is the force generation regulated by calcium?

when troponin C binds calcium, a conformational change occurs of the tropomyosin-troponin complex which normally blocks binding sites on actin for myosin heads