ATP and the Sliding Filament Theory

Edited by Dr. Trevor Bennion

Tug of War, the game is won when a team is able to successfully pull enough rope to their side of the field. This motion replicates the cross bridging of the actin and myosin filaments. Let us say the people all lined up are the myosin strands and their hands are the myosin heads. The actin would then be the rope and the little handholds, sometimes put on the ropes, would be the actin binding sites. The team links on to the rope and starts pulling it towards themselves, sliding the rope past them. To continue bringing more of the rope closer to their side they must let go of one hand, reach for a new handhold, then pull again.

  • ATP is the energy source for metabolic changes in the human body

  • Muscles are layers of compartmentalized tissue

  • Muscles contract through the cross bridging of filaments


Adenosine Triphosphate (ATP) is the energy store in biological systems that produce muscle contraction. The ability to smile or squat is due to the breakdown of ATP. The molecule interacts with the muscle to produce muscular activation due to a mechanism discovered by Andrew Huxley back in 1954 called the Sliding Filament Theory (Powers, Malingen, Regnier, & Daniel, 2021).

Muscles are concentric layers of tissue becoming smaller and smaller until the myofibril is reached. Each myofibril contains long strands of sarcomeres which are the smallest unit of a muscle. The sarcomere contains actin and myosin filaments, along with various other structures. Actin and myosin are double helix strands of protein (Powers, Malingen, Regnier, & Daniel, 2021). These filaments interdigitate with each other where one filament overlaps the other, alternating filaments (Powers, Malingen, Regnier, & Daniel, 2021). In the Sliding Filament Theory, the myosin links to the actin and slides closer to each other (like a ratchet tightening a bolt), shortening the muscle, creating the contraction of a muscle (Powers, Malingen, Regnier, & Daniel, 2021).


Once the linking and ratcheting effect of the myosin heads to the actin binding sites has occurred, to release the myosin head from the actin, so the ratcheting process can repeat to keep bringing the actin and myosin filaments closer together, ATP must come into play. A newly formed ATP will attach to the cocked myosin head and split into adenosine diphosphate (ADP) and a singular inorganic phosphate (Powers, Malingen, Regnier, & Daniel, 2021). This breaking of a molecular bond releases a large amount of energy. The release of energy straightens out the myosin head so more cross bridging, the linking process, can occur.


If the body had an infinite amount of ATP marathons would be much longer, and less impressive, but the body only stores a very small amount (Hargreaves & Spriet, 2020). The body needs to produce more through the process of metabolism which will be discussed in greater detail in a later blog post.


ATP assists in the mechanism of contraction of a muscle called the Sliding Filament Theory.



To get a better understanding of how ATP is built, the structure of muscles, or how the muscles need energy please refer to our other blog posts or subscribe to our online courses!




References:


Hargreaves, M., & Spriet, L. L. (2020). Skeletal muscle energy metabolism during exercise. Nature Metabolism, 817-828.


Powers, J. D., Malingen, S. A., Regnier, M., & Daniel, T. L. (2021). The sliding filament theory since Andrew Huxley: Multiscale and multidisciplinary muscle research. Annual Review of Biophysics, 373-400.