Contractile Mechanisms Flashcards
What does definition of contraction?
Interaction of actin + myosin fuelled by ATP + driven by a rise in [Ca2+]
Describe the structure of skeletal muscle?
Has striations
Number of nuclei
They are quite uniform
Describe the structure of cardiac muscle?
Has striations
Have a single nucleus
Branched shape to individual cell
Cells communicate with each other via intercalated disk zones
Good at connecting to other cells in network allowing smooth communication
Describe the structure of smooth muscle?
Has no striations
Uniform cells with single nucleus
What does striations mean?
Regular overlapping of contractile proteins into well defined units
Describe the structure of myofibril?
Thick filament=myosin
Thin filament= actin + regulatory proteins (troponin + tropomyosin)
Overlap of these filaments= darker diffraction pattern
Little/no overlap = lighter diffraction pattern
M line=protein that holds them together
Describe the thin filament in myofibril?
Actin which is rope like helical arrangement
Lying above the actin is tropomyosin
Tropomyosin is relatively similar structure to myosin
At rest, tropomyosin lies above the myosin binding site on actin
Troponin has 2 binding sites, calcium binding site + tropomyosin
Troponin moves tropomyosin allowing myosin + actin to interact
Describe the structure of myosin?
Single globular molecule with tail + head Has a hinge structure therefore can move depending if it had ATP hydrolysis or not Myosin head (ATPase) => ATP will bind to this head + will be broken down. ADP form will be in slightly different position allowing it to interact with actin
Describe the contraction of skeletal muscle?
Motor nerve is activated
Depolarisation will pass down motor nerve as sodium channel will open
Depolarisation will then arrive at nerve terminal
Ach is stored in vesicles
Ach diffuses a short distance of 40nm + interacts with nicotinic acetylcholine receptors
It binds + you get a kink in channel
This produces influx of calcium ions + depolarisation
What occurs in priming of myosin head in contractile cycle?
Myosin is at rest
ATP is hydrolysed by myosin head ATPase
ATP binding gets hydrolysed + that reaction powers cocking/priming of myosin head
What occurs in power stroke with actin in contractile cycle?
Myosin interacts with actin
Myosin has ADP bound to it so is in different physical position
When myosin binds to actin, you get power stroke
What occurs in relaxation of acto-myosin complex in contractile cycle?
ATP detaches from actin
ATP hydrolysed=> can bind to another actin binding site
Describe cardiac muscle contraction?
Depolarisation opens voltage gated ion channels which leads to influx of Ca2+ ions into cell
Ryanodine receptor are opened by increase of calcium on their external surface as well as physical interaction
No physical interaction between ryanodine receptor + voltage sensing protein
Describe the structure of smooth muscle?
No tubule system Less developed SR Able to sustain contraction for long period Myofilaments connect with dense bodies No troponin but caldesmon, calponin
Describe smooth muscle contraction?
IP3 is released from receptor + it diffuses to IP3 receptor which leads to release of calcium
Calcium channel leads to release of Ca2+ ions
Calmodulin is calcium sensor for Ca2+ ions to one calmodulin which picks up Ca2+ ions
Calmodulin activates myosin Light chain kinase which phosphorylates regulatory area known as light chain
Allows myosin to interact with actin to form actomyosin
Activation of MLCK phosphorylate regulatory MLC at serine 19
Increases ATPase activity of head
Alters structure of myosin
