A2 Biology Helo

Hi Good Morning Britain, "This is TV a.m."

The difference is related to the functions of the two types of RNA, respectively.

mRNA carries the genetic code as a complementary base pair sequence, of which each triplet codes for a particular amino acid. Since a number of proteins are over a 1000 a.a.-s long, the code MUST BE at least 3 times as long in terms of base units (nucleotides).

The function of tRNA is simply to carry the specific amino acid to the mRNA-ribosome complex to be joined to the nascent peptide chain. This only requires a molecule large enough to accommodate an anticodon at one end (to bind to the codon on the mRNA) and a domain that "fits" the specific amino acid at the other end. So these two ends only require a handful of nucleotides, hence the much smaller size of tRNA.

Additionally, it could be argued that in order to transport the aminoacyl-tRNA complex (the combined tRNA with its specific a. a.) efficiently to the RER (site of protein synthesis), it is better to have a smaller molecule for simple diffusion reasons.

M (specialist biology tutor)