. Biophysical science. Biophysics. 8 : 4/ Muscles 149 energy. When this happens, the molecule ATP is split into adenosine diphosphate, ADP, and inorganic phosphate (£). Symbolically, one may write this as ATP - ADP + ® + energy (Readers without previous knowledge of biochemistry should not allow them- selves to be dismayed by this jargon of letters like ATP and ADP. Many people who use them don't know the structural formula represented by these symbols; all one needs to know is the stoichiometric formula written above. The physical forms of ATP and ADP must be very important for their actions,
. Biophysical science. Biophysics. 8 : 4/ Muscles 149 energy. When this happens, the molecule ATP is split into adenosine diphosphate, ADP, and inorganic phosphate (£). Symbolically, one may write this as ATP - ADP + ® + energy (Readers without previous knowledge of biochemistry should not allow them- selves to be dismayed by this jargon of letters like ATP and ADP. Many people who use them don't know the structural formula represented by these symbols; all one needs to know is the stoichiometric formula written above. The physical forms of ATP and ADP must be very important for their actions, but no one yet has succeeded in relating these concepts. The molecule ATP is made up of one molecule of the purine, adenine; one molecule of the pentose sugar, ribose; and three phosphate groups joined by pyrophosphate bonds. Its structural formula is shown below, but the reader unfamiliar with biochemistry is advised to stick to the symbol ATP rather than trying to remember the structure. H—N—H H /^. O t -o—P—o H Adenine plus ribose forms the molecule adenosine. Adenosine plus one phosphate condenses to adenylic acid or adenosine monophosphate, AMP. The latter plus another phosphate condenses to ADP. Energy is released when ATP is split to ADP and when ADP is split to AMP and (?). ) There seems to be no doubt, from a large variety of experiments, that ATP is the source of energy used in muscular contraction. Just how this occurs is not clear. For instance, ATP might be split before the muscle contracts or just as it contracts. An alternative possibility is that the muscle proteins store energy which is used during the twitch and then is slowly built up again from ATP during recovery. ATP might form a complex with the muscle proteins. Recent experiments indicate that several intermediates must exist between ATP and the contractile proteins. Some of the evidence for the direct interaction of ATP comes from experiments with purified myosin and with actin and myosin. If
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