skeletal muscles Flashcards
1
Q
skeletal muscle basics (5)
A
- skeletal- voluntary
- composed of myofibers, which are composed of myofibrils = contractile unitn
- myofilaments make it striated
- 100s-1000s myofibrils make a muscle fiber
- 1500 myosin/ 3000 actin in each myofibril
2
Q
myosin (6)
A
- thick filament
- 1 myosin filament is composed of 200+ myosin molecules
- 6 polypeptide chains: 2 heavy, 4 light
- 2 heavy wrap around eachother to form double helix
- heads protrude to create cross bridges which run length of entire molecule except center (H-zone)
- myosin head is an ATPase enzyme which can cleave ATP as an energy source
3
Q
Actin basics (5)
A
- thin filament
- F-actin= double stranded backbone of the actin filament
3 proteins that make up actin: - G-actin molecules
- Tropomyosin
- troponin complex
4
Q
g-actin (2)
A
- polymerize f-actin
- 1 ADP molecule is attached to each G-actin molecule; these are thought to be the active sites where the cross-bridges on the myosin heads interact
5
Q
tropomyosin
A
in the resting state tropomyosin lie on active sites, preventing contraction
6
Q
troponin complex (5)
A
3 protein subunits:
- troponin I (TnI)- strong affinity for actin
- troponin T (TnT)- strong affinity for tropomyosin
- troponin C (TnC)- strong affinity for calcium
- this attachs the tropomyosin to the actin
- ** when calcium ions attach to troponin C- initiates contraction process because it changes configuration, and moves tropomyosin off binding site**
7
Q
walk along model (5)
A
- before contraction, myosin heads attach to ATP, ATPase activity of myosin head cleaves ATP -> ADP+ P which stays on head and causes confirmation of head to become perpendicular with actin
- cross bridge attachment= now activated myosin head binds to exposed binding site of actin
- power stroke= as myosin head binds, it pivots and pulls on ATP moving it toward center of sarcomere, and releases ADP-P
- cross bridge detachment = new ATP molecule binds to myosin head, changing conformation and detaching head from actin
- cocking of myosin head = new ATP is cleaved and new cycle begins
8
Q
sliding model (4)
A
during contraction the sarcomeres shorten
- z-discs are pulled together
- A-band length stays the same, but successive a-bands get closer together
- I-bands shorten
- H-zones disappear
9
Q
3 functions of ATP
A
- activates walk along model
- pumps Ca back into SR after contraction
- Na/K pump maintain correct ionic environment to propogate AP
10
Q
3 energy sources (to re-phosphorlate ADP)
A
- phosphocreatinine (5-8s)
- glycolysis (up to 1m)
- oxidative metabolism (long, sustained)
11
Q
fast vs. slow fibers (4)
A
- fast fibers = type II/ slow fibers = type I
- fast fibers = “white meat”- large muscles for powerful contraction (chicken breast for flying), slow fibers “dark meat” - for prolonged activity
- fast fibers - extensive SR for rapid release of Ca/ slow fibers- lots of mitochondria (give them the reddish appearance)
- fast fibers- glycolytic metabolism (anerobic)/ slow fibers= oxidative metabolism
