muscles

• In the contraction of a sarcomere calcium ions:

  • interact with the tropomyosin molecule
  • reveal actin-myosin binding sites(on actin)
  • allow myosin heads to bind to exposed sites on actin filament
  • activate ATP hydrolase
• When a muscle fibril is contracted: (banding pattern)

  • H-zone narrows
  • (I-band) light band narrows
• During muscle contraction, ATP hydrolase:

  • breaks down ATP
  • energy released used to break actin-myosin cross-bridges/releases energy for bending of myosin head
• A sarcomere is the distance between adjacent Z-lines
• Slow- twitch fibres:

  • contract more slowly
  • less powerful contractions
  • over longer period
  • endurance
  • large store myoglobin
  • aerobic.... many mitochondria
• Fast=twitch fibres:

  • contract more rapidly
  • powerful contractions
  • for shorter period
  • anaerobic... few mitochondria
  • more myosin filaments
  • large store glycogen
  • phosphocreatine
• Many mitochondria are found in the sarcoplasm:

  • mitochondria-site of aerobic respiration (Krebs/ETC)... release ATP
  • Muscles require energy from ATP to contract
• When a muscle contracts:

  • H zone becomes narrower
  • Z lines become closer together (sarcomere shortens)
  • I band becomes narrower
• Energy is needed for muscle contraction:

  • movement of myosin heads/ breaking of actin-myosin cross bridge
  • reabsorption of calcium ions into endoplasmic reticulum by active transport
• Advantages of high levels of phosphocreatine:

  • phosphocreatine stores phosphate
  • used to generate ATP from ADP in anaerobic conditions
  • Sprinters muscles often work strenuously... oxygen often in short supply
  • allows for production of ATP when aerobic respiration is not possible
  • alactic- does not form lactate
• Role of ATP and phosphocreatine in producing contraction of a muscle fibre:

  • ATP allows myosin to detach from actin/ breaks actin-myosin cross- bridge
  • phosphocreatine allows regeneration of ATP under anaerobic conditions
  • Phosphocreatine releases Pi to join ADP
• Roles of Calcium ions and ATP in bringing about contraction of myofibril:

  • calcium ions cause tropomyosin to move/ expose actin-myosin binding site ON ACTIN
  • calcium ions activate ATP hydrolase
  • hydrolysis of ATP provides energy for the breakage of actin-myosin cross bridges
• Tropomyosin:

  • moves out of the way when calcium ions bind
  • allowing myosin to bind to actin
• Myosin:

  • head of myosin binds to actin and pulls actin past
  • myosin detaches from actin and moves further along actin
• The benefits of endurance athletes having a high proportion of slow muscle fibres: (6)

  • endurance athletes exercise for long periods of time
  • respire aerobically
  • slow fibres are adapted to aerobic respiration
  • many mitochondria.... site of Krebs cycle/ETC... producing large amount of ATP
• Advantage of high glycogen content in fast muscle fibres:

  • glycogen broken down (glycogen=stored glucose).... energy released for anaerobic respiration
  • anaerobic respiration is not very efficient... only 2 ATP per glucose
• Advantage of large number of capillaries in slow muscle fibres:

  • many capillaries give large surface area for oxygen diffusion
  • allows high rate of aerobic respiration