FACTOID # 146: About one-quarter of all nations drive on the left-hand-side of the road. Most of them are former British colonies.
 
 Home   Encyclopedia   Statistics   Countries A-Z   Flags   Maps   Education   Forum   FAQ   About 
 
WHAT'S NEW
RECENT ARTICLES
More Recent Articles »
 

FACTS & STATISTICS    Simple view

  1. Select countries to view: (hold down Control key and click to select several)

     

     

    Compare:

     

     
  1. Select fact or statistic: (* = graphable)

     

     

     

  2. (OPTIONAL) Compare to statistic: (both need to be graphable)

     

     

     

  3. View result as:

     

       
(OR) SEARCH ALL encyclopedia, stats & forums:   

Encyclopedia > Nonsense mutation

In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon (also called a nonsense codon) in the transcribed mRNA, and possibly a truncated (and often nonfunctional) protein product.

Contents
1 Simple example
2 Nonsense-mediated mRNA decay
3 Pathology associated with nonsense mutations
4 External links and references

Simple example

For example, given the following DNA sequence, mRNA transcript, and protein product:

 DNA: TAC TGA GTG GCT CGC GCA TCG ACT mRNA: AUG ACU CAC CGA GCG CGU AGC UGA Protein: Met Thr His Arg Ala Arg Ser Stop

Suppose that a nonsense mutation were introduced at the fourth triplet in the DNA sequence (GCT) causing the guanosine to be replaced with adenine, yielding ACT in the DNA sequence. Since ACT is transcribed to UGA, the resulting transcript would be:

 mRNA: AUG ACU CAC UGA CGC CGU AGC UGA

Furthermore, the resulting protein product would be prematurely stopped since UGA is a stop codon:

 Protein: Met Thr His Stop

The remaining codons of the mRNA are not translated into amino acids because the stop codon is prematurely reached during translation. This can yield a truncated (abbreviated) protein product, which quite often lacks the functionality of the normal, non-mutant protein.


Nonsense-mediated mRNA decay

Despite an expected tendency for premature termination codons to yield shortened polypeptide products, in fact the formation of truncated proteins does not occur often in vivo. Many organisms -- including humans and lower species, such as yeast -- employ a nonsense-mediated mRNA decay pathway, which degrades mRNAs containing nonsense mutations before they are translated into nonfunctional polypeptides.


Pathology associated with nonsense mutations

  • Cystic fibrosis - though rare, a nonsense mutation in the CFTR gene can cause the disease

External links and references

  • Mutations (http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mutations.html)
  • Nonsense mutation (http://www.medterms.com/script/main/art.asp?articlekey=4580) (Medical dictionary)
  • Gatfield D, Unterholzner L, Ciccarelli FD, Bork P, Izaurralde E. "Nonsense-mediated mRNA decay in Drosophila: at the intersection of the yeast and mammalian pathways". EMBO J. 2003 Aug 1;22(15):3960-70. PMID 12881430

  Results from FactBites:
 
Nonsense mutation Summary (991 words)
Unless there is another mutation in a gene that codes for a transfer RNA (tRNA) that allows the suppression of a nonsense mutation, a premature termination of protein synthesis results in the manufacture and release of an incomplete (truncated) and usually nonfunctional protein fragment.
As a result of this particular nonsense mutation, instead inserting the amino acid glutamine into the lengthening amino acid chain during the translation process, the instruction is interpreted as a stop command and the synthesis of the protein is terminated.
Suppose that a nonsense mutation were introduced at the fourth triplet in the DNA sequence (CGA) causing the cytosine to be replaced with thymine, yielding TGA in the DNA sequence.
Point mutation article - Point mutation mutation nonsense mutations sickle-cell anemia hemoglobin gene - What-Means.com (108 words)
A point mutation is a type of mutation that causes the replacement of a single base pair with another pair.
There are several types of point mutations, including nonsense mutations, missense mutations, and silent mutations.
For example, sickle-cell anemia is caused by a single point mutation in the beta hemoglobin gene that converts a GAG codon into GTG, which encodes the amino acid valine rather than glutamic acid.
  More results at FactBites »


 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments
Please enter the 5-letter protection code

Want to know more?
Search encyclopedia, statistics and forums:
 


Lesson Plans | Student Area | Student FAQ | Reviews | Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms.