Molecular motors and contractile structure both play a big and crucial part in the human body and generally, in biology. They are primarily responsible for mobility functions—that is, they’re heavily involved in the mechanisms of movement in living organisms that lets us walk, talk, and go about our everyday functions.
But what are these two scientific terms and what do they mean? Read on to find the answers.
What are molecular motors?
We all know that motors operate in a way that converts the energy they consume into other more useful and relevant forms; such as motion or mechanical work. Molecular motors operate in basically the same way, but this time in a biological setting.
In biology, molecular motors are machines that are responsible for making mobility happen in living organisms. They usually harness chemical free energy that results from the hydrolysis of ATP. This they do in order for them to produce the output of mechanical work.
In fact, molecular motors aren’t only similar to the typical motors that we see and encounter in an everyday setting, but they’re actually even more superior in terms of how energy-efficient they are. Molecular motors are usually operating in the thermal bath, wherein fluctuations induced by thermal noise are significant.
What are some examples of molecular motors?
Some sub-classifications of biologically-important types of molecular motors are:
• Cytoskeletal motors
• Rotary motors
• Polymerization motors
• Nucleic acid motors
• Synthetic molecular motors
Cytoskeletal motors include myosins, dynein, and kinesin. Myosins play a crucial part in muscle contraction, cellular tension production, and intracellular cargo transport. Meanwhile, dynein makes the beating of cilia and flagella possible. Kinesin transports cargo inside cells using microtubules.
Rotary motors include those that are found in bacterial flagellum and in the FoF1-ATP synthase family of proteins. Examples of polymerization motors include actin, which generates force for propulsion, and dynamin, which is responsible for separating clathrin buds from the plasma membrane. There’s also microtubule polymerization, which uses GTP.
Nucleic acid motors are those such as RNA polymerase, DNA polymerase, helicases, topoisomerases, SMC proteins, and RSC and SWI/SNF complexes. Lastly, synthetic molecular motors are those that are lab-created. They have been made with the end objective of yielding rotation and eventually, generating torque.
Myofibrils compose the individual muscle fibers in the body. Myofibrils, meanwhile, are made up of three types of protein. These three types are contractile, regulatory, and structural proteins.
Contractile proteins make muscle contraction happen by generating the force needed for it. Contractile proteins in the myofibril include actin and myosin. Basically, contractile structures are akin to muscle tissues in the skeletal muscle.
Muscle cells have, over time, grown to carry out the highly-specialized function of contraction. As a contractile structure, it must contract quickly and repetitively to perform complicated movements.
Contractile structures also include contractile fibers. Through extended coiled-coil domains in the heavy chains, some myosin isoforms like myosin II form assemblies. Actin thin filaments and thick filaments associate with each other to create contractile bundles. You can find these bundles both in non-muscle and muscle cells.
Contractile structures vary in size and thickness. And specifically for contractile bundles, around 10 to 300 individual actin filaments are used.