contractile cells

Question 1

how does the sliding filament model work?

Answer 1

• Binding - Myosin cross bridge binds to actin
• power stroke - cross bridge bends pulling thin myofillaments inwards
  -detachment - cross bridge detaches at end of power stroke and returns to OG confirmation
• binding - cross bridge binds to more distal actin molecules and the cycle is repeated

Question 2

what is the role of calcium is muscle contraction

Answer 2

• calcium removes tropomyosin from actin allowing myosin to bind to actin
• tropomyosin acts as a molecular suppressor preventing myosin to binding to actin
  -calcium binds to troponin - C

Question 3

describe the contractile mechanism of cardiac and skeletal muscle

Answer 3

DRIVEN BY THE REMOVAL OF SUPPRESSIVE TROPOMYOSIN
- Tropomyosin prevents myosin from interacting with actin
Troponin has a calcium binding site=Troponin-C and a tropomyosin binding site =Troponin-T
- At low Ca2+ levels TROPOMYOSIN is in the way preventing the interaction between actin and myosin - - At high Ca2+ levels Ca2+ binds to Troponin-C and this increases affinity for tropomyosin
- Tropomyosin binds to Troponin-T pulling it away from actin
-This allows myosin and actin to interact

Question 4

describe the contractile mechanism of smooth muscle

Answer 4

ACTIVATION OF MYSOIN = A GO MECHANISM
- The myosin in smooth muscle is a different isoform to that of the skeletal and cardiac muscle
- The myosin has a low ATPase activity and a low affinity for ATP
- This is until [Ca2+] goes up
- Calcium + Calmodulin activates the myosin light chain kinase (MLCK)
- This phosphorylates regulatory MLC
- This increases the ATPase activity of myosin and alters its structure allowing it to react with actin causing contraction

Question 5

Skeletal muscle vs cardiac muscle contraction

Answer 5

Skeletal muscle: physical interaction b/w DHP and RyR, no Ca2+ entry
Cardiac muscle: opening Ca2+ channel promotes CICR, Ca2+ entry

Question 6

what causes the rise in calcium

Answer 6

• Skeletal muscle excited causes the release of chemicals from MOTOR NEURONS
• This activates receptors + DEPOLARISE
• This opens ion channels and the depolarisation goes down the TRANSVERS T-TUBULE
• Dihydropyridine receptors stop interacting w Ca2+ ion channels
  = voltage movement which causes Ca2+ to spill out of SR