What do muscle fibers form from
a syncytium; single, multinucleated cell, no cell membranes bet cells to interrupt signaling.
What does skeletal muscle use for fuel
fatty acids and ketone bodies and glucose (only when it has to)
What does it use maximally
muscle glycogen. it can withstand anaerobic conditions better than other types of muscle
If cardiac muscle becomes ischemic:
it dies; myocardial infarction. Don’t have glycogen stores. No cori cycle.
What does skeletal muscle have as a reserve for ATP
phosphocreatine
What are featurs of cardiac muscle
- totally aerobic metabolism
- oxidizes glucose, and ketone bodies
- stores some energy in form of phosphocreatine
what are markers for myocardial infarction
- creatine kinase (CK)
- Glutomate oxaloacetate transaminase (GOT)
- Troponin
- Lactate Dehydrogenase
What happens when you have onset of chest pain? which enzymes get released?
Troponin goes up really high at earliest time point, then creatine kinase and then lactate dehydogenase last.
whats the LD flip (lactate dehydrogenase)
5 diff isoforms.
Reticulo endothelial form is at highest level typically. If you see cardiac form go above that, its typical of a heart attack.
The I band is usually just:
actin (thin filaments only) does not span entire lenth of thin filaments
How many polypeptide chains does myosin have
6; 2 heavy chains (fibrous; dont dissolve) that have large globular “head” which is ATPase
4 light chains; complex with heads–>regulatory
how is myosin formed
- two heavy chains coil from carboxy terminus.
- amino terminus forms globular heads.
- light chains ass with head region.
- cleavage with trypsin & and papain results in heavy and light meromyosin.
what are the thin filaments composed of
actin, troponin, and tropomyosin.
what does tropomyosin do
regulates actin/myosin interaction
what does troponin do
binds Ca++
what is actin c omposed of
- G actin: ind globular actin molecules
2. F actin: fibrous complex of G actin molecules
what does each ind G actin have bound to it
ADP; however ATP/actin interaction is NOT directly involved in muscle contraction.
which troponin binds to caclium
Troponin C
Z line
where thin filaments attach
M line
where thick filaments attach
what is A band composed of
thick filaments; spans entire length inc region of overlap with thin filaments
what doesnt change upon contraction
A band
what dissapears during contraction
H zone
What gets smaller during contraction
I band and H zone
the biggset polypeptide identified;
titin; protein that extends from M line to Z line (half the length of sacromere); regulates sarcomere length and prevents over extension
When nothing is bound to myosin it has high____for actin. When ATP binds, it releases, it has ____affinity. When ATP is hydrolyzed we start to get some affinity for ____and myosin head gets cocked and changes conformation and starts to bind to actin. _____phosphate falls off and we tighten affinity then ____falls off and we go back to original conformation which forms the powerstroke.
affinity; NO; actin; inorganic; ADP
Explani muscle contraction
- nerve impulse stimulates muscle cell
- muscle cell releases intracellular Ca++ from SR
- Ca++ binds to troponin C, changing its conformation
- change in troponin C results in conformational change in tropomyosin
- exposes myosin binding sites on actin
what is sarcolemma
plasma membrane of muscle cell and has deep invaginations called T-tubules which are in close proximity to SR which releases calcium.
Smooth muscle does not contain ____
troponin; tropomyosin is regulated with a calcium/calmodulin (CaCM) regulated protein called caldesmon
Smooth muscle has a unique myosin light chain called
myosin p-light chain; CaCM activates a myosin light chain kinase (MLCK) enzyme that phosphorolates myosin p- light chain and activates it.
Ca++/calmodulin modulates many proteins including:
cyclic nucleotide phosphoiesterase; lowers level and cAMP and shuts down PKA and activates PKC signaling
what are targets of Ca++/calmodulin protein kinsae
- myosin light chain kinase
- cAMP specific phosphodiesterase
- NO synthase
- PI-3 Kinase
How does smooth muscle contraction work
- activate reg protein
- binds to caldesmin which moves tropomyosin out of the way so actin and myosin can bind
- Need to phosphorolate myosin light chain via MLCK which is also act by CaCM.
