Sliding filament theory Flashcards

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1
Q

Process of muscle contraction

A

1- Ca2+ ions diffuse into myofibrils from sarcoplasmic reticulum + bind to tropomyosin causing it to move up, exposing the binding sites on actin
2- Myosin heads attach to actin filaments forming an actinmyosin cross bridge. ATP-> ADP+ Pi, Pi is released
3- Myosin head bends pulling actin filaments along, ADP is released - known as power stroke (makes sarcomere shorter so muscle contracts)
4- ATP binds to myosin head causing it to detach from actin binding site (Z lines move closer together + sarcomere shortens so muscle cells contract
5- Hydrolysis of ATP to ADP + Pi by ATPase provides energy needed to re-cock myosin head to original position ready to form a new cross bridge. Ca2+ ions are actively transported back to sarcoplasmic reticulum + tropomyosin returns to original shape + covers binding sites

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2
Q

What happens to banding pattern in sarcomere when it contracts

A
  • A band stays the same length as myosin filament doesn’t shorten
  • I band + H zone get shorter as actin filaments are pulled over myosin filaments
  • Z lines get closer together as sarcomere gets shorter overall
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3
Q

How is ATP constantly generated

A

Aerobic respiration- most ATP is generated via oxidative phosphorylation, only happens when there’s enough O2 (good for long periods of exercise)
Anaerobic respiration- ATP is made rapidly by glycolysis in sarcoplasm (useful for short periods of intense exercise, lactate can cause muscle fatigue)
Phosphocreatine- stored in muscle cells + rapidly provides Pi to add to ADP to produce ATP. Used in short bursts of vigorous exercise as runs out quickly. Anaerobic + doesn’t form any lactate, creatine can be broken down into creatinine + removed by kidneys - high levels may indicate kidney damage

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4
Q

Compare actin + myosin structure

A

Actin:
- Has binding sites for myosin heads called actin-myosin binding sites
- Tropomyosin forms a long chain which coils around the actin filaments - helps filaments move past each other but blocks actin-myosin binding sites when muscle is relaxed
Myosin:
- Has many globular heads that are hinged so they can move back + forth using energy from ATP
- Each head has a binding site for actin + ATP

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5
Q

What must happen for muscle contraction to occur

A
  • Action potential from motor neurone has to depolarise sarcolemma , then wave of depolarisation travels down T- tubules to sarcoplasmic reticulum. Depolarisation triggers sarcoplasmic reticulum to release Ca2+ ions into sarcoplasm
  • Influx of Ca2+ ions triggers muscle contraction
  • Ca2+ ions are needed to move tropomyosin + expose actin- myosin binding sites so myosin heads can bind to actin. No Ca2+, no muscle contraction as filaments can’t slide past one another
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