Lecture 5: Proteins of Sarcomere and Scaffolding Flashcards
each myofibril is ~ ______ in diameter
~1-2 (mu)m in diameter
in a fiber (cell) of 50 (mu)m diameter, there are ~ _____ fibrils
8000 fibrils
thin filaments
actin strands and a z-line
structural protein in a z-line or disk
alpha actinin
where do actin filament attach?
on either side of the z disk
alpha actinin converts ___ sided actin filaments to ____ sided structure
alpha actinin converts a 6 sided actin filament to a 4 sided structure (z-disk)
globular (G) actin
- globular (G) actin ~ 350/filament
- decrease ATP –> ADP (90% of cells ADP)
Filamentous (F) actin
a helix
tropomyosin
50/filament covers 7 G-actin
Troponin
-50/filament every tropomyosin
T
tropomyosin
C
Ca++ 4 binding sites
I
inhibitory
thick filament
myosin
myosin heavy chain
~ 300 rods/thick filament
-different isoforms (ATPase)
Light chains LC1, LC3
essential
Light chain LC2
regulatory
myosin head
- 2 heads per myosin molecule
- binding site with actin
- ATP enzyme
spacing of heads: the heads rotate at ___ degrees
the heads rotated at 60 degrees
why are the myosin heads rotated at 60 degrees?
allows 4 head groups to possibly interact with 1 thin filament?
M-line attachments
M-filaments (myomesin) M4 crosslinks (creatine kinase)
titan
- sarcomere support protein
- largest protein in our bodies
- found in both skeletal and cardiac muscle fibers
- tethers the myosin filament within the sarcomere
- acts like a spring
- source of much of the passive elastic force in skeletal muscle
- major mechanism for the Frank-starling mechanism in the heart
nebulin
- integral part of actin strands
- acts as a ruler or template to regulate thin filament length during sarcomere assembly
- nebulin-knockout mice
nebulin-knockout mice
- die postnatally
- have reduced thin filament length
- postnatal sarcomere disorganization and degeneration
- impaired contractile function
cytoskeleton
- anchors myofibrils to eachother
- anchors myofibrils to plasmalemma
- anchors basement membrane to plasmalemma
intermediate filaments of the cytoskeleton
anchor myofibrils to eachother
desmin, vimentin, synemin
intermediate filaments of the cytoskeleton desmin, vimentin, synemin
- wrap around z-disk
- keep z disks of adjacent fibrils in register during contraction
dystrophin
Duchenne (1861-72’) muscle weakness
anchoring myofibrils to plasmalemma
cytoskeletal filaments
capping protein, vinculin, talin
anchoring basement membrane to plamalemma
transmembrane proteins (integrins), fibronectin receptor, glycoproteins, fibronectin, laminin
with an absence of what protein will one die?
dystrophin
