Lipidlar, ya'ni yog'li molekulalar ko'pchilik hayvonlar hujayra membranalari massasining taxminan 50% ni tashkil qiladi, qolgan deyarli barchasi oqsildir. Lipid ikki qavatining 1 mkm × 1 mkm maydonida taxminan 5 ×106 lipid molekulasi yoki kichik hayvon hujayrasining plazma membranasida taxminan 109 lipid molekulasi mavjud.