MUSCLE I Flashcards
what is the purpose of structural proteins in muscle
to transmit movement or force outside of the cell
name the 4 structural proteins discussed
titin, nebulin, a-actin and dystrophin
describe the structure of titin
large, elastic protein
2 titin molecules running parallel to myosin
what is the function of titin?
anchors thick filament to Z-disc (main)
also acts as molecular ruler during myogenesis, helps with passive length tension and prevents overstretching
what is the structure of nebulin?
long inelastic protein with 2 strands for each actin, running the length of each actin
what is the function of nebulin?
anchors thin filament to Z disc
what is another (secondary) function of nebulin?
can be used to determine the length of the actin filament
what is the purpose of alpha-actinin?
attachment point for actin filaments to z-disc
what are dystrophins?
focal contact points between sarcomere and membrane/extracellular matrix
what type of myosin is in muscle?
myosin II
what is the structure of myosin II?
hexameric protein with 2 heavy chains and 2 light chains
when is myosin “bent”?
when bound to ADP and Pi
when is myosin “straight”?
when bound to ADP only
function of troponin T
binds to tropomyosin, positions actin and exposes myosin binding sites
function of troponin I
binds to actin, prevents myosin from binding actin
function of troponin C
calcium binds causing a conformational change that disrupts actin-TnI interaction
function of caldesmon
acts similar to TnT in smooth muscles
function of calponin
acts similar to TnI in smooth muscle
A-band
entire length of thick filament
H-zone
thick only
I-band
thin only
what happens to the A-band, H-zone and I-band during muslce contraction?
H and I shorten, A is stable
what is the consequence of increased muscle fiber length?
decreased cross linkages, decreased force of contraction
what is the consequence of decreased muscle fiber length?
thick filament clashes with z-disc, less lesion and less force of contraction
describe the steps in muscle contraction (5)
1-ATP binds to actomyosin and disrupts bond between them
2- myosin hydrolyzes ATP to ADP and Pi
3- Pi is released from myosin and power stroke occurs
4- ADP released from myosin, causing myosin to rotate further
5- ATP free to bind and start cycle over
what is the power stroke in muscle contraction?
dissociation of Pi is the power stroke
what controls the rate of muscle contraction?
dissociation of ADP controls the rate of contraction
describe slow twitch type I muscle (6)
small, fatigue resistant, red myoglobin, lots of mitochondria, Ox metabolism and low glycogen
describe fast twitch type IIA (6)
intermediate, fatigue resistant, red myoglobin, lots of mitochondria, Ox metabolism and high glycogen
describe fast twitch IIB/IIX (6)
large, fatiguable, white myoglobin, few mitochondria, glycolytic metabolism and high glycogen
what does endurance training change regarding muscle fibers? (4)
increases type IIA, increases mitochondria, increases myoglobin, decreases type IIX
what neurotransmitter is involved with skeletal muscle contraction?
acetylcholine
describe the interaction between DHP receptors and RyR-1 receptors in skeletal mm
there is a physical interaction between DHP receptors and RyR-1 receptors in skeletal mm that leads to Ca release from sarcoplasmic reticulum
what is the role of calcium in skeletal muscle contraction?
binds troponin C to increase Pi dissociation and allow power stroke to occur
what neurotransmitter is involved with cardiac muscle contraction? what receptors?
norepinephrine, beta-adrengeric receptors
discuss RyR-2 receptors
found in cardiac muscle, involved in calcium induced calcium release
what is chronotrophy?
heart rate
what is inotrophy?
heart contractility
what is lusitrophy?
heart relaxation (rate)
which receptors are responsible for calcium-induced calcium release in smooth muscle cells?
IP3 receptors on sarcoplasmic reticulum
what does calcium bind in smooth muscle cells?
calmodulin, Rho-A kinase, caldesmon and calponin
what is the function of calcium-calmodulin?
activation of myosin light chain kinase (MLCK) to phosphorylate myosin and allow it to interact with actin
what is the function of Rho-A Kinase?
Rho-A Kinase inhibits myosin light chain phosphatase (MLCP) so that the light chains can remain phosphorylated for a prolonged period
what causes myosin to return to the the relaxes state in smooth muscle?
MLCP (dephosphorylates)
what can activate MLCP?
cGMP
what are the functions of caldesmon and calponin in smooth muscle?
expose tropomyosin and allow MLC to bind
what causes muscular dystrophy?
defective focal adhesion proteins leading to weak contraction, disruption of membranes
what is malignant hyperthermia?
autosomal, myopathy secondary to defect in RyR-1 causing uncontrolled mm contraction and hyperthermia
what causes familial hypertrophic cardiomyopathy?
single amino acid mutation in the myosin heavy chain that changes ATP hydrolysis and decreases contractile force leading to wall hypertrophy
what receptors are reduced in the setting of heart failure?
RyR-2
how doe viagra work?
inhibits breakdown of cGMP (through inhibition of PDE5) that enhances the relaxation of smooth mm allowing blood to collection for erection
