Module 4: Lecture 2 Flashcards
what is the A band based on?
the thick filaments and how far they travel
- your thin filaments are within it as well
why is the I Band called the light band?
because there is no thick filaments in it so light is allowed through it
does muscle contraction always cause a ‘shortening’ of the muscle?
no
what does contraction refer to?
an active state in which your actin and myosin are forming cross bridges and generating force
what is the sliding filament mechanism caused by?
cross-bridge cycling
why can a cross bridge form?
because of the overlap of the filaments and the binding sites
what is the sliding filament mechanism a result of?
the action potential stimulating skeletal, smooth and cardiac muscles
what is linked to internal changes in calcium release and contraction?
changes in the membrane potential of muscles
what is the signal that allows your action and myosin cross bridges to begin to form and actually generate force?
when cytosolic calcium increases in a resting myofibre
what is the only purpose of the action potential in the muscle fiber?
to stimulate the release of calcium
are thin filaments a single polypeptide chain?
no, it is a quaternary structure, meaning it is made up of multiple different protein chains
what is the single polypeptide chain component of actin called?
globular actin (G-actin)
what is a single polypeptide chain?
a long chain of amino acids that fold back in on itself
how can ‘F-actin’ be formed?
if you polymerize a whole bunch of g-actins into a long chain
what is formed from two F-actins intertwining?
an actin helix
- the main structure of thin filaments
is there a binding site on every actin molecule?
yes, it is where the myosin head can physically attach to the actin molecule and where the cross bridge is formed
how do we make sure that myosin does not attach to the actin to form a cross bridge binding sites at rest?
we physically block the binding sites with tropomyosin that intertwine on the actin helix
what is the sensor on the actin for when the muscle is activated or not?
troponin
what are the regulatory molecules?
troponin and tropomyosin
what does troponin regulate?
whether tropomyosin is blocking or not blocking that active site
how many actin molecules can one single tropomyosin molecule block?
seven actin molecules
- all regulated by one single troponin protein
each tropomyosin molecule is held in such _________ binding position by the _________ molecule.
- inhibitory
- troponin
what are the three troponin subunits?
- T
- I
- C
which troponin subunit is physically interacting with the tropomyosin molecule itself?
troponin T
- this is what is holding it in close proximity to the actual tropomyosin molecule
which troponin subunit keeps it in the inhibitory state and ensures that the binding sites are blocked?
troponin I
when we want muscle contraction, which subunit of troponin do we have a conformational change in?
troponin I subunit that removes inhibitory blocking
which troponin subunit is responsible for sensing when a muscle contraction should be occuring?
troponin C
- calcium binds to troponin C and induces the conformational change to remove the inhibition
what is our thick filament made up of?
a whole bunch of myosin molecules with the head regions in both directions away from M line
what is a single myosin molecule composed of?
two large polypeptide heavy chains that are intertwined with their tail regions in this helix form and four smaller light chains
- they combine to generate a large molecule with two globular heads and one long tail
- two large polypeptide heavy chains and four smaller light chains
where on a myosin molecule is the site for where a cross-bridge with actin forms?
globular heads
what are the two binding sites on a single large polypeptide heavy chain globular head?
- actin binding site
- ATP binding site
the light chains on the polypeptide heavy chains are for what?
they are specialized proteins that stabilize the head and also act as a site of regulation
- critical for stability
- they are meant to stabilize the myosin head and the interactions and regulate its activity
what are the two light chains on the heavy chains called?
one is called the essential light chain and the other is called the regulatory light chain
what energy is used for generating your cross bridges/contraction?
ATPase
why are the myosin molecules in the two ends of each thick filament oriented in opposite directions?
so that the power stroke of the cross-bridges move the thin filaments toward the centre of the sarcomere
what happens during the power stroke?
the head of the myosin physically bends and pulls the myosin head inward
what is the sequence of events that allow for the cross-bridge cycle?
- binding between the myosin head and the thin filament
- movement of the cross-bridge through power stroke, cross bridge bends, pulling thin myofilament inward
- detachment of the cross-bridge: detach myosin from the thin filament
- re-energize the myosin head so it can re-attach to a thin filament to repeat the cycle
every time a myosin undergoes power stroke, it is pulling ____________________________________.
that actin filament closer and closer towards the M line
why do we have two heads on a single myosin molecule?
to generate more force than a single head
what is the A Band defined as?
the width of your thick filaments
from rest to contracted sarcomere, what happens to the A-band, I-band, H-zone, and overall sarcomere length?
A-band: no change
I-band: shorten
H-zone: shorten
Sarcomere: shorten
