The Growing Chain: Translation Elongation Process

If a new amino acid needs to be added to the chain, then it must enter the ribosome at a specific docking station. If the A site is the designated entry point for the next tRNA, then the incoming molecule binds there.

If the mRNA was synthesized 5' to 3' and the start codon is at the 5' end, then the ribosome must move toward the 3' end to read the rest of the message.

If proteins are made of amino acids linked by covalent bonds, then the ribosome must catalyze a specific reaction. If this chemical link is a peptide bond, then it is the primary connection formed.

If elongation is a cycle that builds a chain, then it must involve matching tRNAs, joining amino acids, and moving the ribosome; however, unzipping DNA and splicing RNA happen during transcription and processing, not translation.

If molecular "switches" called elongation factors are needed to move the ribosome and ensure accuracy, then they must use a specific nucleotide fuel. If translation machinery specifically hydrolyzes GTP for these tasks, then GTP is the energy source.

If "P" stands for peptidyl, then that site is dedicated to holding the tRNA that is attached to the peptide chain. If the A site receives new amino acids, then the P site must be the one holding the progress made so far.

If the ribosome has finished adding an amino acid and needs to clear the A site for the next one, then it must physically move. If this movement shifts the mRNA-tRNA complex, then the step is called translocation.

If the mRNA codon acts as the instruction and the tRNA anticodon acts as the key, then they must fit together chemically. If they form matching hydrogen bonds, then the ribosome accepts the tRNA as correct.

If the ribosome is an assembly line, then it needs specific "rooms" for entry (A), holding (P), and exiting (E). There are no standard "S" or "G" sites in ribosomal structure.

If "E" stands for exit, then it is the location where empty tRNAs are moved after their cargo is gone. If the tRNA is no longer attached to the chain, then it is released into the cytoplasm to be reused.

If the ribosome is made of both protein and RNA, then one component must act as the enzyme. If the rRNA in the large subunit performs the catalytic work of joining amino acids, then it is a ribozyme.

If the process of translation results in many peptide bonds being formed, then the product is a "poly" (many) "peptide."

If elongation is the second stage of translation, then the ribosome and mRNA must already be present. If amino acids are needed, then "charged" tRNAs must deliver them; however, DNA and RNA Polymerase are only for transcription.

If all nucleic acid pairing involves strands running in opposite directions to form hydrogen bonds, then the mRNA and tRNA must be opposite. If mRNA is 5' to 3', then the anticodon must align 3' to 5'.

If a protein chain has a beginning (N-terminus) and an end (C-terminus), then new units must be added to the end. If translation proceeds by adding the new amino acid to the carboxyl group of the previous one, then it grows toward the C-terminus.

If translation initiation begins at the cap or start codon near the beginning of the transcript, then the ribosome moves forward from that point. If that starting point is the 5' end, then that is where the process begins.

If the goal is to build a chain, then the existing chain in the P site must be moved to the new amino acid in the A site. If this transfer happens, then the tRNA in the A site now holds the entire, longer chain.

If more supplies and helper proteins are available, then the process moves faster. If multiple machines (ribosomes) work on one message at once, then more protein is made; however, cold and lack of fuel (GTP) slow the process.

If a stop codon (UAA, UAG, or UGA) does not have a matching tRNA, then the elongation cycle cannot continue. If the cycle breaks, then the process must terminate.

If the process involves linking amino acids in a specific linear sequence based on mRNA, then the result is the first level of protein structure. If this chain is the product, then it is a polypeptide.