how is the codon AUG differentiatied in it's multiple meaning?

Question

AUG codes for both Met. and initiation, when mRNA is being read, how does it know wether AUG will be for the start or to make Met.?
thanks

Answer 1

Actually, it's NOT differentiated.

All tRNA is transcribed with that group at the front (well... except for some bacteria that have alternate start groups). All those AUGs are turned into methionines at the start of every protein.

The fix for all this arises AFTER the protein is completely finished. Another protein comes along whose sole purpose is to snip the N-terminal (the starting) methionine off every protein that's made.

It's a good thing that cells can recycle!

Nor is it the only modification of this sort made after the fact. Lots of proteins have extra bonds made (particularly between subunits) and sometimes whole sections cut away. All this only helps create the massive diversity needed in protein shapes and uses!

Answer 2

Quite simple - the first amino-acid in the chain must be a specially modified methionine. If the chain hasn't been started yet and the ribosome comes across an AUG, it will insert this special methionine and start elongation (which it does because only that particular tRNA can properly interface with the initiation machinery). If the chain HAS been started, then an ordinary met-tRNA will incorporate (the special one can't incorporate without the initiation machinery to help it).

Answer 3

if that is true...that aug codes for more than one tahn the only way it would read to make met. would be that it is not proceded by the ending codon.