role of ATP and phosphocreatin

give the key features of fast skeletal muscle fibres:

• short contraction-relaxation cycle

• large store of Ca²⁺ and more sarcoplasmic reticulum

• fewer blood capillaries around fibres

• ATP largely obtained by anaerobic R

• fewer, smaller mitochondria more evenly distributed

• larger amount of glycogen and phosphocreatine

• higher rate of ATP hydrolysis in myosin heads ∴ more actomyosin bridges formed per sec

• quickly become fatigued - more lactate formed

give the key features of slow skeletal muscle fibres:

• long contraction-relaxation cycle

• smaller store of Ca²⁺ in sarcoplasmic reticulum

• dense network of blood capillaries around fibres for O₂ supply and glucose for aerobic R

• ATP largely obtained by aerobic R

• many, large mitochondria nearer surface of fibres

• small amount of glycogen

• slower rate of ATP hydrolysis in myosin heads

• resistant to fatigue, as less lactate formed

what is phosphocreatine?

molecule stored by muscles that can be used for the rapid production of ATP over short periods

give and justify the 3 sources of ATP for muscle contraction:

• aerobic R - long periods of low intensity exercise

• anaerobic R - short periods of hard exercise due to lactate buildup

• phosphocreatine:

  • ATP made by phosphorylating ADP, adding a PO₄^3- group taken from phosphocreatine

  • short bursts of vigorous exercise as runs out after a few seconds

  • anaerobic and alactic

what does it mean for the ATP-phosphocreatine system to be alactic?

doesn’t form any lactate

what is the eqn for the reaction of ADP w/ phosphocreatine?

ADP + phosphocreatine → ATP + creatine