Saturday, 2 March 2013

Translation of Genes

Now that we've got transcription under our belts, we can now look at translation.  Translation is where the information that was stored in genes (DNA) is used to create a protein.  Note that the DNA information had to be copied (transcribed) into a new molecule: RNA.  It's very common for students to be unclear about what processes occur during transcription and which ones are translation.

When you're talking about promoters and terminators, enhancers, silencers, and RNA polymerase, you're talking about transcription.  In eukaryotes, RNA splicing, mG capping, and the poly-A tail are all involved in modifications of the transcript (RNA strand).  These events occur BEFORE translation.

Note that only when we're dealing with translation do we start to worry about start codon and stop codons.  Most people have dealt with codons and anticodons in their introductory biology classes, but in my lecture below I look them over again quickly.  Note that I'm adding a little more complexity to these introductory concepts:  I want everyone to know that there's special parts of mRNA - the 5'UTR and the 3'UTR (untranslated regions).  The borders of these are defined by the start and stop codons.

In translation, there's also a set of steps to getting the ribosome to load unto the mRNA.  The ribosome is made of rRNA and protein.  The small subunit in prokaryotes has a piece of rRNA that's complementary to the 5'UTR upstream of the start codon:  the Shine-Dalgarno box.  Eukaryotes have something similar (the Kozak sequence, but which has the start codon embedded within the consensus sequence).  After the small subunit has bound, the first tRNA with its amino acid (methionine in eukaryotes, formylmethionine in prokaryotes) will bind to the start codon, then the large subunit attaches.

Prokaryotes also transcribe and translate their genes simultaneously.  Without a nuclear envelope to partition the RNA polymerase in one compartment (the nucleus) and the ribosomes in another (the cytoplasm) we can see transcription of mRNA that occurs even as it's being manufactured!  Eukaryotes have spacial separation, which may be why they are able to modify their mRNA so extensively before translation.

So, without more buildup, here are the video lectures for "translation"!

Part 1:  Structure of the ribosome

Part 2:  Using the Code

Part 3:  Cracking the Code

Part 4:  Posttranslational Modification and Shipping

No comments:

Post a Comment