You can tell which way round an actin filament is by labelling it with fragments of myosin molecules, which bind to it in a very particular way, and then lookin

You can tell which way round an actin filament is by labelling it with fragments of myosin molecules, which bind to it in a very particular way, and then looking at it really, really closely. People describe the appearance as arrowheads or chevrons, although to me it looks like ears of wheat: http://jcb.rupress.org/content/jcb/79/3/846.full.pdf http://jcb.rupress.org/content/jcb/79/3/846.full.pdf From that, there is a convention of drawing actin filaments with chevrons, such as in this paper by my old supervisor: https://www.semanticscholar.org/paper/Molecular-mechanism-of-actin-dependent-retrograde-Cramer/93f65377bba9e3c1801c5c0e474718a79eebcb25 https://www.semanticscholar.org/paper/Molecular-mechanism-of...