00:01
So let’s go through the process
of cross-bridge cycling.
00:05
Just to orient you, the actin fiber
is going to be listed in small dots,
and these are the polymers
associated with actin filament.
00:17
The myosin will be the thick
filament and will also
include a myosin head, and
we’ll only include one,
but know there are a plethora of myosin heads
that will be contracting continuingly,
more like you would think of a ship
being rowed by a number of individuals.
00:35
So let’s start at this process and
then walk it around in a circle.
00:40
We’re starting off here with the myosin
head bound to the active site on actin.
00:46
Here, we have a
dephosphorylated ATP or an ADP.
00:53
What we want to do at this particular
point is undergo a power stroke.
00:59
How this happens is as soon as the
myosin head binds to this active
site on actin, you’ll get a
conformational change of this protein.
01:10
It then moves actin as the conformational
change in the myosin head happens.
01:18
At this point, you will also
release your ADP molecule.
01:25
ATP then binds to it, which causes
a release or a disassociation
between the active site of
actin and the myosin head.
01:37
This process will then
undergo a cleaving of
ATP or sometimes referred
to as a hydrolysis.
01:45
That hydrolysis of ATP then provides the
energy to undergo a conformational change
that basically recocks the myosin head to
a tension spot to have potential energy.
02:01
Once this myosin head
is in this position,
it has the energy to undergo
another power stroke.
02:09
It then binds to the active site on
actin as long as calcium is present,
and by binding this site,
it will also cause a conformational
change or a power stroke.
02:24
This process just keeps
going on and on and on
as long as you have
enough ATP to cause the
disassociation of the
myosin and actin filaments,
enough ATP to cause the
hydrolysis of that
molecule to cause the
cocking of the myosin head,
and as long as you have enough calcium which
keeps that active site on actin open.