Differences in translation between prokaryotes and eukaryotes

let's talk about some of the differences between how translation happens in prokaryotic cells and how it happens in eukaryotic cells and I want to focus mainly on the mRNA just before it's ready to be translated so let's start with our prokaryotic mRNA and let's look at our five prime side first so we have this yellow part right here and that's the non-coding region and it's called the non-coding region because the Ribe of the ribosome is not actually going to read that part so that particular sequence of amino acids is not that important and then after the non-coding region we have the shine-dalgarno sequence and the shine-dalgarno sequence is the site that the ribosome is going to recognize and bind to so let's restore ribosome right over here this is where the prokaryotic ribosome is going to bind and then after the shine-dalgarno sequence we have another non-coding region just going to abbreviate it and C R and then we have our start codon which is typically Aug so that tells us to start and so the ribosome is going to start translating it's going to read this entire section put together the corresponding polypeptide chain until it hits the stop codon which tells it to stop translating and then we have another non-coding region let's look at our eukaryotic mRNA and so it's pretty similar but you can see there are some differences so we'll start with our five prime side first so you see this red nucleotide right over here that's the five prime cap and the five prime cap is simply a guanine nucleotide so I'm going to draw a G inside guanine and it's going to have a methyl group somewhere on the molecule so I'm going to draw a methyl group and the bond between this guanine and the nucleotide right near it is a bond that's different than the bond you typically find between two nucleotides and so that's really all the five prime cap is and the five prime cap is actually the ribosomal binding site in eukaryotes so that means that in eukaryotes the ribosome is going to recognize this particular part and bind to it so after the five front cap we have this other non-coding region which the ribosome is not going to translate and then the ribosome is going to hit the start codon again Aug tell have to start and it's going to start translating so it's going to translate this entire section until it hits the stop codon and then we have another non-coding region and then we hit something that looks different than what we've seen in the prokaryotic mRNA so this section with blue nucleotides and that's called the poly a tail and the poly a tail is a bunch of nucleotides that are all A's or ad the knees so I'm going to draw these inside all these nucleotides and the poly a tail is actually pretty long so it's typically anywhere between a hundred and two hundred and fifty nucleotides long so that's pretty long so I didn't exactly draw it to scale and the purpose of both the five prime cap and the poly a tail is to prevent this mRNA from being degraded by enzymes so acts as this kind of signal that does not allow enzymes to break it down or degrade it and so you might be wondering well what about prokaryotic mRNA how come they don't have anything similar to prevent it from being degraded and the brief answer that question is that in prokaryotic cells transcription that's an R and translation both happen in the same place so prokaryotic cells don't exactly have a nucleus they have this you know excited soul and transcription and translation are happening in the same place and not only are they happen in the same place but they can actually be happening at the same time so you can have a piece of mRNA that's being formed and while it's being formed a ribosome will attach to it and begin to translate it but in eukaryotic cells things are a little bit different so transcription happens in the nucleus and translation happens in the cytoplasm where there are ribosomes and so the mRNA after it's made has to travel from the nucleus to the cytoplasm to where the ribosomes are and so because it's traveling this relatively large distance it's going to encounter a lot of different things including enzymes that might break it down and so it needs this extra protection to prevent it from being damaged in any way there's one more difference I want to talk about and how translation happens in prokaryotes and eukaryotes and that is what the first amino acid in the polypeptide chain will be so in prokaryotic cells the first amino acid in the chain is always a formyl methionine and for Allah thymine is simply the amino acid Metheny but with a formal group attached and in case you don't remember what a formal group looks like it looks like that in eukaryotic cells the first amino acid in all the polypeptide chains is simply Metheny and it's interesting to note that formal methane is actually acts as an alarm system in a human body so if you have some bacterial cells in your body that were damaged in any way there would be these formal methods floating around and that tells your body that there are bacteria around and it's going to trigger an immune response