Translation

[grayfalcon89]

Hi,

 

I need quick help on understanding transcription and translation. I think I know what transcription is and maybe translation is but here is what I think they are:

 

In transcription, DNA's replication that in which RNA involves. This means that instead of DNA replicating the same thing, RNA gets involved and RNA is made, which has antisequence of DNA. Suppose DNA is ACG then RNA is UGC. By the way, thymine is replaced with uracil in RNA.

 

In translation, decoding RNA messages into polypeptide chain, or simply, rewriting in protein.

 

But my question is, what does transfer RNA do? I know that messenger RNA carries out the information for DNA around the cell and this is what basically happens in transcription, right? But why is transfer RNA needed in here for translation? My book quotes:

 

Because the three nucleotides on transfer RNA are complementary to the three nucleotides on messenger RNA, the three transfer RNA nucelotides are called the anticodon.

 

Why is it complementary to messenger RNA? Perhaps this is like asking why RNA complementary to DNA? I can answer that question because RNA goes in place of another DNA so in order for them to match, they have to be complementary or antisequence of DNA. But why is in this case of messenger RNA and transfer RNA?

 

Like why can't transfer RNA takes exact form of messenger RNA and just go to where codes of amino acids are and decode it?

 

Perhaps this might help so i'll put also:

 

Attached to each transfer RNA molecule is the amino acids specified by the codon to which it base pairs. By matching the transfer RNA anticodon to the messenger RNA codon, the correct amino acid is put into place. Each transfer RNA acts like tiny beacon for its specific amino acids

 

No clue at all.

 

Thanks for the help.

[kixxer]

But my question is' date=' what does transfer RNA do? I know that messenger RNA carries out the information for DNA around the cell and this is what basically happens in transcription, right? But why is transfer RNA needed in here for translation?[/quote']

 

Well, there are loads of "different" tRNAs, and all have the capability to bind a specific amino acid at their 3´-OH terminus. So basically, you need to have tRNAs for all 21 amino acids which are needed for the building of proteins. tRNAs are somewhat different to other types of RNA-molecules, since they are heavily modified and consist of a few very unusual bases. All of these modifications provide the tRNA-molecules with more stability, so that they don´t get degraded as quickly as mRNA for example. All tRNA´s posess a region called the anti-codon. The anti-codon conists of three bases, which are complementary to the sequence they have to identify on the mRNA. So here again, all the tRNAs for different amino acids have a different anti-codon region

 

 

Ok, the translation is performed by organelles called ribosomes in the cytoplasma of the cell. The Ribosome consists of two subunits, a small (40S) and a bigger one (60S) in eukaryotes.

 

Ribosomes bind at the 5´-beginning of the mRNA and start scanning the mRNA for a Start-codon (AUG), a place where the protein synthesis starts. They posess two "binding grooves", where tRNA´s can be bound. The "AUG" start-sequence is identified by the ribosom which has the Met-starter-tRNA bound to one of it´s binding grooves. Met-tRNA has a anticodon that identifies AUG on mRNA, so basically all proteins synthetised in the body begin with a Methionin (which can of course be cleaved of later)

 

(This part is very difficult to put into words, at least for a non-english-speaker:():

 

Ok,so now you have the first amino acid of your protein in the right place, and the ribosome knows it has to start with protein synthesis. Then what happens is that the ribosome scans the next three bases on the mRNA, to see what amino acids will come next in the protein sequence. This scanning is always done with the tRNAs, many tRNAs bind to the groove but only one (with the correct anti codon in respect to the mRNA sequence, will be bound stron enough to continue with protein synthesis; HERE you need the anticodon to be complementary, otherwise there will be no binding!!!!).

 

SO then, when the ribosome knows which amino acid comes next, it simply binds the new amino acid and the MET from the start together (using different enzymes). Then the ribosome moves one base-triplett further in 5´->3´direction on the mRNA, and again the correct tRNA will be searched for. This cycle repeats as long as the ribosome (or the tRNA) detects a stop codon on the mRNA, signalling the end of protein synthesis.

 

uuhh...hope this wasn´t too confusing. I tried to upload some pictures to the elongation process of ribosomes, but I couldn´t, they seemed to be too big, can somebody change this? Or otherwise, check my site at the link below, if you want to I can post them there. Just let me know.

 

anyways, hope this is of help:)

 

greets from Finland,

kix

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http://www.biologia.fi

[Kh112]

Videos help a lot in understanding...This one is ok.