Hello, my name is Dr. Jeffrey Kieft and for
the next lecture in this series on understanding ribosomes,
I'm going to focus on the topic of translation initiation with
a particular emphasis on the structures that
drive this very important biological mechanism.
Ribosomes are amazingly complex biological machines that are of central importance.
They catalyze the formation of the important peptide bond,
and they do so with remarkable fidelity and efficiency.
As you already know, the ribosomes are
large RNA protein complexes consisting of two sub-units.
The small ribosomal sub-unit shown here contains
the decoding center where the tRNAs interact with the messenger RNA.
The large ribosomal sub-unit contains the catalytic center of the ribosome,
where the peptide bond is made when
the two ribosomal sub-units are bound to one another within the assembled ribosomal,
the message passes directly between them,
as do the tRNAs during the process of translocation.
As the mechanistic details of ribosome function continue to emerge,
it is also important to think about the fact that ribosomes
operate within a larger mechanistic framework so for the moment,
let's think about ribosomes within a larger context.
Let's turn our attention to the overall mechanism of translation,
which can be divided into several phases.
The first phase of translation is the initiation step.
As the name implies,
initiation is the process of recruiting the ribosome and starting protein synthesis.
The next phase is elongation, during elongation,
the ribosome is actively moving along the messenger RNA,
decoding the message and producing the growing polypeptide chain.
Termination refers to the phase in which the process
stops because the ribosome senses a stop codon.
At that point, the ribosomal sub-units can dissociate and they then be used again to
initiate translation of different messenger RNA
or perhaps re-initiate on the same messenger RNA.
During my lecture, I'm going to focus on the initiation phase,
that is the very important phase by which the entire process of translation begins.