Contractile Proteins and Motors Flashcards
What are the major protein players in muscle contraction
Myosin
Microfilaments (actin)
Tropomyosin
Troponin
Myosin II structure
2 heads - ATP, binds actin
neck
Tail - forms a filament
Who are the thick and thin filaments
Myosin - thick
Actin - thin
What does tropomyosin do
Controls myosin binding sites
Where does tropomyosin bind
In the groove between actin strands
How does tropomyosin do its job
In low Ca state –> blocks myosin binding site on actin
in high Ca state –> moves to reveal myosin binding site on actin
How does tropomyosin do its job
In low Ca state –> blocks myosin binding site on actin
in high Ca state –> moves to reveal myosin binding site on actin
Who is troponin
Complex that can bind with Ca, associated with tropomyosin
Who doesn’t have troponin
Smooth muscle
What does troponin do
controls tropomyosin position in response to Ca levels
Run down of the basic relationship between the 4 proteins
Troponin binds to Ca controls –> tropomyosin position - controls –> myosin binding to actin
What is the sarcoplasm filled with
repeating arrays of filaments (myofibrils) made of actin and myosin
Where does the intercellular Ca live
The SR
What are t-tubules
Transverse invaginations in the sarcolemma (plasma membrane)
They transmit the action potential to the myofilaments
What is the area where the sarcolemma and T-tubules come into proximity called
Terminal cisterna
What is a sarcomere
The contractile unit if the muscle cell
Why does skeletal (and cardiac) muscle look striated
Ordered, repeating arrangements of actin and myosin –> myofilaments
What do thick filaments contain
Myosin
What do thin filaments contain
Actin, tropomyosin, troponin
Dark bands:
A bands, thick filaments and overlapping thin filaments
Light bands
i bands, thin filaments
M line:
H band , connection between adjacent mysosin filaments
z discs:
Define the ends of the sarcomere, site of attachment of plus end of actin filaments
How are the myofilaments arranged in the sarcomere
6 actin around 1 myosin
In basic terms, what makes muscles contract
Sarcomeres shortening as myosin walks along actin
Basics of the cross-bridge cycle:
ATP binding releases myosin head from actin –>
ATP –> ADP rotates myosin head —>
Myosin head binds actin filament –>
“Power stroke” - release of P and stored elastic energy moves actin filament left –>
ADP –> ATP - myosin released
What is happening in rigor mortis
Myosin head is attached to actin, no ATP available to release it
What regulates contraction
Ca ions
How does Ca regulate contraction (low Ca)
Low Ca: myosin binding site is blocked by tropomyosin which is held in place by troponin
How does Ca regulate contraction (high Ca)
High Ca in cytoplasm –>
Ca binds to troponin –>
Conformational change –>
Tropomyosin moved off of myosin binding site on actin
What controls the release of Ca
Action potentials - stimulate release of Ca from the SR
What protein does smooth muscle lack
Troponin
What binds sarcoplasmic Ca in smooth muscles
Calmodulin
