Muscle Flashcards
Titin
Elastic protein that connects myosin to Z-disk. Spring-like action keeps myosin centered in sarcomere
Nebulin
Inelastic protein attached to Z-disk, and parallels actin
Myomesin
Myosin binding protein that holds myosin filaments in register at M-line
C protein
Myosin binding protein with function similar to myomesin
Alpha-actinin
Bundles actin filaments into parallel arrays.
Anchors actin filaments to Z-disk
Desmin
Intermediate filament that helps bind myofibrils to each other. Encircles Z-disk. Interlinked by plectin protein
Dystrophin
Actin binding protein. It may anchor muscle membrane proteins to actin
Duchenne muscular dystrophy patients
Lack dystrophin
What regulates in vivo polymerization of actin?
Thymosin 𝝱-4 & profilin
What does the A band contain?
Thick myofilaments & thin myofilaments
What does the I band contain?
Thin myofilaments (attached to Z disk)
What does the H band contain?
Myosin (no heads) & creatine kinase
What does creatine kinase do?
Catalyzes:
ADP + phosphocreatine –> ATP
What is the M line?
Region of myomesin linking with myosin
What is the Z disk?
Attachment region of thin filaments. It contains 𝝰-actinin
What does tropomyosin do?
Binds 3 troponin peptides, Tn-T, Tn-I, and Tn-C
What does Tn-T do?
Binds Tn complex to tropomyosin
What does Tn-I do?
Inhibits binding of actin to myosin, with help of tropomyosin
What does Tn-C do?
When Ca ions bind Tn-C, it releases the Tn-I-tropomyosin inhibition of the actin activation of myosin ATPase
What is tropomyosin?
Protein dimer (35K MW) that lies in grooves of actin helix
What does plectin do?
Interlinks filaments of desmin
What is 𝝰𝝱-crystallin?
A heat-shock protein that protects desmin from stress-induced damage
Sarcoglycanopathies (limb-girdle muscular dystrophies)
Mutations in genes for sarcoglycans causes defective assembly of sarcoglycans. This disrupts the interaction with other proteins & association of sarcolemma with the ECM
Cardiac muscle cell
Single, centrally located nucleus
What makes cardiac muscle fibers unique?
Their composition of several cardiac muscle cells joined end-to-end by intercalated disks
What comprises intercalated disks?
A transverse portion–containing fasciae adherens (actin filament anchor site) and macula adherens (desmosomes)–that binds adjacent cells together, and a lateral portion (gap junctions) that ionically couples adjacent cells
What three changes manifest in cardiocytes following a myocardial infarction?
- eosinophilic cytoplasm
- pyknotic nuclei (condensed chromatin)
- inflammatory cells infiltrate after 3 days
What characterizes smooth muscle cells?
Spindle shape, but may branch
Single, central, oval nucleus, w/1 or more nucleoli
Surrounded by basal lamina, may secrete collagen & elastin
Does not have sarcomeres
Where are single smooth muscle cells found?
These myoepithelial cells of ectodermal origin are found: around sweat, salivary, mammary & lacrimal glands
Where is smooth muscle of mesodermal origin found?
In circulatory, digestive, respiratory & reproductive tracts
Where is smooth muscle of ectodermal origin found?
In the iris & cilliary body of the eye
What comprises the functional equivalent of a Z disk in smooth muscle?
Membrane associated & cytoplasmic dense bodies that contain 𝝰-actinin
