difference between mRNA, tRNA and rRNA?

rRNA functions, along with certain proteins, to make up ribosomes. Ribosomes are the cellular "workbenches" where polypeptides ('proteins') are synthesized. Turns out the the part of the ribosome that actually links amino acids together is made or rRNA, and not protein.

mRNA functions to deliver the message for building a specific polypeptide to ribosomes; the base sequence in the mRNA molecule specifies the order that amino acids are to be incorporated into the growing polypeptide.

tRNAs function to transfer the correct amino acids to the ribosome. At any one time, the ribosome has an empty position (in the A site), with 3 bases of the mRNA associated with it. Those bases are called a codon. A tRNA molecule with the complementary 3-base anticodon is the only one that can dock into the A site. And because an enzyme charged that particular tRNA molecule with the correct amino acid, the tRNA has brought to the ribosome the needed amino acid to incorporate into the chain.

In eukaryotes, all three of the RNAs mentioned are present in the nucleus, because that is where they are synthesized. tRNA and mRNA do not function in the nucleus - they are exported to the cytoplasm where they perform their functions as mentioned above. rRNA does stay in the nucleus for a while, because it combines with certain proteins to make ribosomal subunits. Then the ribosomal subunits are exported from the nucleus into the cytoplasm - once an mRNA binds with a ribosomal subunit, the other ribosomal subunit combined with those two and a fullblow ribosome results, and translation begins.

rRNA - ribosomes mRNA - the RNA that is transcribed off the DNA that code for protein. tRNA - the RNA that carries specific amino acids of which the ribosomes use to make protein.