FACTOID # 16: In the 2000 Presidential Election, Texas gave Ralph Nader the 3rd highest popular vote count of any US state.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Synonymous substitution

A synonymous substitution (also called a silent substitution) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the amino acid sequence produced is not modified. Base pairs, of a DNA molecule. ... For other meanings of this term, see gene (disambiguation). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...


Redundancy in DNA

Proteins translation involves a set of twenty amino acids. Each of these amino acids is coded for by a sequence of three DNA base pairs called a codon. Because there are 64 possible codons, but only 20 amino acids (as well as a stop signal, indicating that translation should stop), some amino acids are coded for by 2, 3, 4, or 6 different codons. For example, the codons TTT and TTC both code for the amino acid phenylalanine. This is often referred to as redundancy of the genetic code. There are two mechanisms for redudancy: several different transfer RNAs can deliver the same amino acid, or one tRNA can have a non-standard "wobbly" base in position three of the anti-codon, which recognises more than one base in the codon. Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... Phenylalanine is one of the standard amino acids. ... The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ... RNA codons. ... Phe redirects here. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ...


In the above phenylalanine example, suppose that the base in position 3 of a TTT codon got substituted to a C, leaving the codon TTC. The amino acid at that position in the protein will remain a phenylalanine. Hence, the substitution is a synonymous one.


Substitution versus mutation

Although mutation and substitution are often used interchangeably, there is a subtle but important difference. A nucleotide mutation is a base change (whether synonymous or non-synonymous) such that the mutant and wild-type forms coexist in a population. A nucleotide substitution is a base change between two related species. Thus, a mutation only becomes a substitution after it has increased to 100% frequency, or fixed, in the species.


Synonymous substitutions and evolution

When a synonymous or silent mutation occurs, the change is generally neutral, meaning that it does not affect the fitness of the individual carrying the new gene to survive and reproduce. Redundancy of the genetic code provides some protection against the effect of mutations. Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ... It has been suggested that mutant be merged into this article or section. ...


Substitutions that are not synonymous are often detrimental to the host cell. For instance, a mammalian cell might have a gene coding for a protein that regulates cell division. A mutation that results in a change to the methionine codon that marks the beginning of the gene's open reading frame may cause the gene to become inactivated. The protein that regulates cell division would not be produced, and the cell would grow unchecked, resulting in a tumor cell. Drawing of the structure of cork as it appeared under the microscope to Robert Hook from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... This does not adequately cite its references or sources. ... Methionine (Met, M. C5H11NO2S) is an essential nonpolar amino acid, and a lipotropic. ... An open reading frame or ORF is any sequence of DNA or RNA that can be translated into a protein. ... Tumor or tumour literally means swelling, and is sometimes still used with that meaning. ...


  Results from FactBites:
 
Race - Wikipedia, the free encyclopedia (12166 words)
Thus, the concept of "race" afforded by these techniques is synonymous with ancestry, broadly understood.
Today, the word "Latino" is often used as a synonym for "Hispanic" (the identification of Spanish-speaking countries in the Americas as "Latin America" was first promoted by supporters of Maximilian as emperor of Mexico in 1864.
Maximilian was installed by the French emperor Napoleon III as a way of extending French influence in the Americas; since French and Spanish are both derived from Latin, the French identified Spanish-speakers as "Latin" in order to emphasize a fictive kinship with the French, and in the hope — unfulfilled — of legitimating Maximilian).
CATHOLIC ENCYCLOPEDIA: Universities (10734 words)
That the terms had become practically synonymous at the beginning of the fourteenth century appears from a statement of Clement V, 13 July, 1312, to the effect that the Archbishop of Dublin, John Lech, had reported that in those parts there was no scolarium universitas vel studium generale.
About 1300 also the expression mater universitas was used by the Oxford masters, and these may have taken it from a document of Innocent IV (6 Oct., 1254) in which the pope speaks of Oxford as faecunda mater.
During the seventeenth and eighteenth centuries, various modifications were introduced in the courses of study; new chairs were founded and the financial condition improved.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

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

 


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, 1022, m