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Flashcards in skeletal muscles Deck (11)
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1
Q

skeletal muscle basics (5)

A
  1. skeletal- voluntary
  2. composed of myofibers, which are composed of myofibrils = contractile unitn
  3. myofilaments make it striated
  4. 100s-1000s myofibrils make a muscle fiber
  5. 1500 myosin/ 3000 actin in each myofibril
2
Q

myosin (6)

A
  1. thick filament
  2. 1 myosin filament is composed of 200+ myosin molecules
  3. 6 polypeptide chains: 2 heavy, 4 light
  4. 2 heavy wrap around eachother to form double helix
  5. heads protrude to create cross bridges which run length of entire molecule except center (H-zone)
  6. myosin head is an ATPase enzyme which can cleave ATP as an energy source
3
Q

Actin basics (5)

A
  1. thin filament
  2. F-actin= double stranded backbone of the actin filament
    3 proteins that make up actin:
  3. G-actin molecules
  4. Tropomyosin
  5. troponin complex
4
Q

g-actin (2)

A
  1. polymerize f-actin
  2. 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:

  1. troponin I (TnI)- strong affinity for actin
  2. troponin T (TnT)- strong affinity for tropomyosin
  3. troponin C (TnC)- strong affinity for calcium
  4. this attachs the tropomyosin to the actin
  5. ** 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
  1. 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
  2. cross bridge attachment= now activated myosin head binds to exposed binding site of actin
  3. power stroke= as myosin head binds, it pivots and pulls on ATP moving it toward center of sarcomere, and releases ADP-P
  4. cross bridge detachment = new ATP molecule binds to myosin head, changing conformation and detaching head from actin
  5. cocking of myosin head = new ATP is cleaved and new cycle begins
8
Q

sliding model (4)

A

during contraction the sarcomeres shorten

  1. z-discs are pulled together
  2. A-band length stays the same, but successive a-bands get closer together
  3. I-bands shorten
  4. H-zones disappear
9
Q

3 functions of ATP

A
  1. activates walk along model
  2. pumps Ca back into SR after contraction
  3. Na/K pump maintain correct ionic environment to propogate AP
10
Q

3 energy sources (to re-phosphorlate ADP)

A
  1. phosphocreatinine (5-8s)
  2. glycolysis (up to 1m)
  3. oxidative metabolism (long, sustained)
11
Q

fast vs. slow fibers (4)

A
  1. fast fibers = type II/ slow fibers = type I
  2. fast fibers = “white meat”- large muscles for powerful contraction (chicken breast for flying), slow fibers “dark meat” - for prolonged activity
  3. fast fibers - extensive SR for rapid release of Ca/ slow fibers- lots of mitochondria (give them the reddish appearance)
  4. fast fibers- glycolytic metabolism (anerobic)/ slow fibers= oxidative metabolism