Question

Hey people, I have a question:
DNA replication is more accurate than transcription, which is in turn more accurate than translation. Can you please enlighten me on the reasons and if possible what are the mechanisms involved which are responsible for the accuracy of each one of those processes.

Thank you.

Answer 1

In this lacture Prof. Eric explains the processes your are interested on.

http://ocw.mit.edu/courses/biology/7-012-introduction-to-biology-fall-2004/video-lectures/lecture-11-molecular-biology-2/

You might also want to watch Lecture 12.

Good Luck!

Answer 2

DNA is a hereditary material, which is inherited to next generation so there need to b perfection in the process of DNA replication. RNA and proteins are not inherited if they r defective they r gona affect only the individual not its progeny, that is y transcription and translation r not that perfect as replication.
Hope this helped.

Answer 3

Hey Thays and Nazima. Thanks for your help. That link was really helpful Thays. Actually, what I was looking for, was not really a holistic approach of why DNA replication is more accurate than transcription and so on but rather what make these processes more accurate than the others. What I concluded from some readings is that DNA replication has a proofreading mechanism exhibited by the DNA polymerase III. As we all know, DNA is synthesized in the 5' to 3' direction by DNA polymerase III. Moreover, it uses its 3' to 5' exonuclease activity to remove any incorrect base added and uses back its 5' to 3' polymerase activity to try add back the right base. This proofreading activity makes it more accurate than the other mentioned processes 'cause they don't have this particular ability. Also, transcription involves direct reading from a DNA template and the complement base pairs are added accordingly to the mRNA. However, due to no proofreading mechanism like that of DNA replication, there's no guaranty that the base pairs added in the mRNA are exactly the complements of those found in the DNA template. This is why transcription is less accurate than replication. For the translation process, it's pretty easy to determine why this process is not so much accurate. There are many codons which code for one particular amino acid. The fact that it is relatively not so specific makes this process less accurate than the others.

I hope that I got it right. Please do lemme know what you think about this particular answer.

Answer 4

Hi @Kayne, Excellent response. The only thing I would have to say is - what you mentioned about translation (many codons for one amino acid, aka a degenerate code) is not necessarily linked to a loss of accuracy.

This is from Wikipedia:
"The genetic code has redundancy but no ambiguity (see the codon tables above for the full correlation). For example, although codons GAA and GAG both specify glutamic acid (redundancy), neither of them specifies any other amino acid (no ambiguity)."

In other words, even though many codons may specify the same amino acid, no codon specifies multiple amino acids. Or in math terms, it's like a function, right? So the characteristic of the code being degenerate need not imply it being in accurate, I believe. Unfortunately though, I can't supply you with the exact mechanism that leads to a (relatively) inaccurate translation process.

It is worth looking at things from an evolutionary perspective, if only to cement what you have already deduced. Because there is (usually) only one set of the genome in a cell, there is an extremely high selective pressure to maintain copying fidelity, through mechanisms you've mentioned. IIRC, after you account for the various proofreading mechanisms, there is, on average, one mutation per 10^9 base pairs. However, there is little selective pressure on extremely accurate mechanisms for translation and transcription. In transcription, say there's an error in your mRNA - this will, maybe, lead to errors in the proteins directly produced from that mRNA. While there's a small chance that that's dangerous for the cell, there's much more leeway here because the cell is coninuously producing new mRNA and degrading the old ones.

Translation gives the cell even more leeway. If there's a istake during translation, you'll get one improperly folded protein, which will soon be broken down. As the cell is constantly making new proteins, a relatively inaccurate translation process is not nearly as detrimental as an inaccurate DNA replication process.

Answer 5

Thanks @kma230 ... :) That's really helpful..:)

Answer 6

Yw :) Good luck!

Answer 7

@Kayne You got it. The process controlled by DNA polymerase III has an accuracy in adding the right base of 99,9 %. And this is terrible, when you think about how many times the DNA is replicated in a cell! We would have a lot of mutations!!! Hence, this exonuclease activity is a great mechanism which gives the odd accuracy found in the DNA replication we all know. `cause we need more energy to add a wrong base, and once it happens it`s easier to take this wrong base off than to take a right base off. It`s perfect and beautiful!