wˌʌt dɪtˈɜːmɪnz wˈɛðɚ ðɪ ˈɛndz ɡɹˈoʊ ɔːɹ ʃɹˈɪŋk ɪz ɛntˈaɪɚli dᵻpˈɛndənt ɔnðə saɪtˈɑːsəlˌɪk kˌɑːnsəntɹˈeɪʃən ʌv ɐvˈeɪləbəl mˈɑːnoʊmɚ sˈʌbjuːnˌɪts ɪnðə sɚɹˈaʊndɪŋ ˈɛɹiə.
What determines whether the ends grow or shrink is entirely dependent on the cytosolic concentration of available monomer subunits in the surrounding area.