revisionlad
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Why is tRNA molecule(70-80 nucleotides) a smaller molecule than mRNA(75-3000 nucleotides)??

Thanks.
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macpatgh-Sheldon
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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)
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revisionlad
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(Original post by macpatelgh)
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)
Wow thank you so much for the detailed response!
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