What is the common building blocks of steriods?

Answer 1

Two molecules of farnesyl pyrophosphate are dimerized to form squalene which is a triterpene. All steroids originate from squalene. The squalene is converted to the sterol lanosterol to from which animal and fungi steroids are derived. Plant steroids originate from the sterol cycloartenol. The bottom line is that steroids come from squalene. Squalene itself originates from acetyl CoA. Hope this helps.

Answer 2

The common building block of steroids is the sterol unit. Cholesterol is the simplest form.

Answer 3

Isoprene molecules CH2=C(CH3)-CH=CH2