Why does 50S 30S=70S for ribosomes?

Well. It's a very good question. It kept me wondering​ for a long time untill I came to know the science behind this. Ok. Let's come to the picture. read more

The S in the ribosomal subunits stand for sevdberg units named so in honour of the scientist Theador Svedberg and represent the different sedimentation rates of the ribosomes during centrifugation. While the larger subunit sediments at 50S and the smaller at 30S together they sediment at 70S. Hence 50S+30S=70S and not 80S. read more

Answer Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit. read more

The unit of measurement used to describe the ribosomal subunits and the rRNA fragments is the Svedberg unit, a measure of the rate of sedimentation in centrifugation rather than size. This accounts for why fragment names do not add up: for example, prokaryotic 70S ribosomes are made of 50S and 30S subunits. read more