Errors in DNA replications!!! I can not understand it. Please help!?

Question

When DNA replicated, errors in copying may occur, leading to the substitution of one base for another in the DNA sequence. Why these errors often have little effect on the polypeptide produced by translation & transcribtion of that particular DNA sequence?

Answer 1

First, as noted by others above, repair mechanisms may correct the errors. Second, there is redundancy in the genetic code such that many point mutations in the third base of a codon will not change the amino acid. For example, the codons for glycine are GGA, GGC, GGT, and GGG. Third, the genetic code often uses similar codons to encode structurally similar amino acids, so that sometimes a mutation in the second base of the codon will have little effect on protein structure. Finally, while certain key residues in a protein may be critical to its function, mutation of many others may have no functional effect.

Answer 2

Because there are "safety mechanisms" so that some of the errors in the bases are not translated into the proteins that are ultimately produced.

Your textbook probably has a chart of the "genetic code", please check it when reading this. If you don't have a copy with you, here it is:

http://library.thinkquest.org/C0123260/basic%20knowledge/images/basic%20knowledge/RNA/genetic%20code.jpg



The genetic code is the equivalence between sets of bases (codons) and aminoacids.

Note that there are only 20 aminoacids, but there are 64 possible combinations of 4 bases in 3 positions (i.e. codons). 3 of these possible combinations are "stop" codons, which leaves 61 codons for 20 aminoacids.

Thus, the genetic code is "degenerate" (= each aminoacid corresponds to more than one codon).



If you look at the different codons that code for the same aminoacid, you'll see that they usually differ by one base only (and it's usually the base occupying the third position). This means that even though one base may be substituted for another during replication, there are good chances that the resulting codon will still code for the same aminoacid.

As a result, when translation happens, there is no change in the protein primary structure.

Answer 3

They are LESS damaging than most other types of replication errors - we are a talking about a point mutation - but they are definately damaging.



They are often less damaging, because they can be mis-sense (same amino acid sequence formed, therefore same end product - it's as if no replication error occured), and therefore do not always destroy or change the final product. Also, it is only ONE base-pair, so the proof-reading and repair enzymes and mechanisms are MORE LIKELY to find it and FIX it before it is transcribed and translated.

Answer 4

The structure of proteins is encoded as one triplet of bases, called a codon, per amino acid. Since there are only twenty amino acids that occur in proteins, while there are 64 (= 4^3) possible codons, it's not hard to imagine that there must be several amino acids that can be encoded by more than one codon.



If you look at my source, you can see that for instance the amino acid leucine can be encoded as UUA, UUG, or CUx (where x can be any base). So if the codon CUC is 'corrupted' during the copying process to CUU, it still codes for leucine, and transcription might still yield the same protein.

Answer 5

first - there is a proofreading activity of the polymerase after replication to catch that error (transcription) so the error would be corrected



second - if translated and the substituted AS "fits" into the protein and doesnt change its catalytic abilities - no problem



translation problems are most often frame shift not wrong amino acids - not working proteins are degraded and recycled rapidly

Answer 6

Did you consider only reading your textbook? in case you're lost in this, you obviously have not been interpreting in any respect because no man or woman asks how hydrogen bond works, you woulda reported hydrogen bonds, or something of that count number. please actual examine something previously only asking, you obviously were no longer paying interest in college in any respect or setting up any attempt because the approach isn't that demanding to comprehend, nor complicated. its only steps that make sense and also you purely gotta learn it no longer something demanding to comprehend