Types of RNA
- unmodified RNA formed right after transcription.
- RNA that carries assembly code for polypeptide.
- translates RNA code to specific amino acid.
- forms ribosomes that assemble the polypeptide (a RNA enzyme!).
- Polypeptides made of sequence of 20 amino acids.
- Problem: how to specify 20 amino acids with just four nucleotides?
- Triplets work... 43=64.
- Redundency, start and stop codes built into code.
Eukaryotic Translation Step-by-Step
- mRNA and initiator tRNA bind to small ribosomal subunit.
- Large ribosomal subunit arrives. We are good to go.
- Ribosomal subunits made of rRNA and proteins.
- Somewhere in cytosol, a tRNA finds and binds to its unique amino acid.
- tRNA (and amino acid) with correct anticodon binds to mRNA codon.
- Ribosome scoots mRNA along, peptide bond forms.
- Expended tRNA is released.
- Repeat steps 5 thru 7 until stop codon reached.
- mRNA and ribosomal subunits disassociate. Party's over.
- Several ribosomes might be cruising along a mRNA.
- Polypeptide will be folding as its being made.
- Other functional groups or molecules might be added to polypeptide.