errata 24989

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 </media>
 <caption>Instructions on DNA are transcribed onto messenger RNA. Ribosomes are able to read the genetic information inscribed on a strand of messenger RNA and use this information to string amino acids together into a protein.</caption></figure><section id="fs-id2000981">
 <title>The Genetic Code Is Degenerate and Universal</title>
-<para id="fs-id1290387">Each amino acid is defined by a three-nucleotide sequence called the triplet codon. Given the different numbers of “letters” in the mRNA and protein “alphabets,” scientists theorized that single amino acids must be represented by combinations of nucleotides. Nucleotide doublets would not be sufficient to specify every amino acid because there are only 16 possible two-nucleotide combinations (4<sup>2</sup>). In contrast, there are 64 possible nucleotide triplets (4<sup>3</sup>), which is far more than the number of amino acids. Scientists theorized that amino acids were encoded by nucleotide triplets and that the genetic code was <term id="term-00003">“degenerate.”</term> In other words, a given amino acid could be encoded by more than one nucleotide triplet. This was later confirmed experimentally: Francis Crick and Sydney Brenner used the chemical mutagen proflavin to insert one, two, or three nucleotides into the gene of a virus. When one or two nucleotides were inserted, the normal proteins were not produced. When three nucleotides were inserted, the protein was synthesized and functional. This demonstrated that the amino acids must be specified by groups of three nucleotides. These nucleotide triplets are called <term id="term-00004">codons</term>. The insertion of one or two nucleotides completely changed the triplet <term id="term-00005">reading frame</term>, thereby altering the message for every subsequent amino acid (<link target-id="fig-ch15_01_05"/>). Though insertion of three nucleotides caused an extra amino acid to be inserted during translation, the integrity of the rest of the protein was maintained.</para>
+<para id="fs-id1290387">Each amino acid is defined by a three-nucleotide sequence called the triplet codon. Given the different numbers of “letters” in the mRNA and protein “alphabets,” scientists theorized that single amino acids must be represented by combinations of nucleotides. Nucleotide doublets would not be sufficient to specify every amino acid because there are only 16 possible two-nucleotide combinations (4<sup>2</sup>). In contrast, there are 64 possible nucleotide triplets (4<sup>3</sup>), which is far more than the number of amino acids. Scientists theorized that amino acids were encoded by nucleotide triplets and that the genetic code was “<term id="term-00003">degenerate</term>.” In other words, a given amino acid could be encoded by more than one nucleotide triplet. This was later confirmed experimentally: Francis Crick and Sydney Brenner used the chemical mutagen proflavin to insert one, two, or three nucleotides into the gene of a virus. When one or two nucleotides were inserted, the normal proteins were not produced. When three nucleotides were inserted, the protein was synthesized and functional. This demonstrated that the amino acids must be specified by groups of three nucleotides. These nucleotide triplets are called <term id="term-00004">codons</term>. The insertion of one or two nucleotides completely changed the triplet <term id="term-00005">reading frame</term>, thereby altering the message for every subsequent amino acid (<link target-id="fig-ch15_01_05"/>). Though insertion of three nucleotides caused an extra amino acid to be inserted during translation, the integrity of the rest of the protein was maintained.</para>
 <para id="fs-id1565817">Scientists painstakingly solved the genetic code by translating synthetic mRNAs in vitro and sequencing the proteins they specified (<link target-id="fig-ch15_01_04"/>).</para>
 <figure id="fig-ch15_01_04"><media id="fs-id2989543" alt="Figure shows all 64 codons. Sixty-two of these code for amino acids, and three are stop codons.">
 <image mime-type="image/png" src="../../media/Figure_15_02_05.png" width="400"/>

modules/m66523/index.cnxml

@@ -11,7 +11,7 @@
 </metadata>
 
 <content>
-<para id="fs-idm26761872">People did not understand the mechanisms of inheritance, or genetics, at the time Charles Darwin and Alfred Russel Wallace were developing their idea of natural selection. This lack of knowledge was a stumbling block to understanding many aspects of evolution. The predominant (and incorrect) genetic theory of the time, blending inheritance, made it difficult to understand how natural selection might operate. Darwin and Wallace were unaware of the Austrian monk Gregor Mendel's 1866 publication "Experiments in Plant Hybridization", which came out not long after Darwin's book, <emphasis effect="italics">On the Origin of Species</emphasis>. Scholars rediscovered Mendel’s work in the early twentieth century at which time geneticists were rapidly coming to an understanding of the basics of inheritance. Initially, the newly discovered particulate nature of genes made it difficult for biologists to understand how gradual evolution could occur. However, over the next few decades scientists integrated genetics and evolution in what became known as the <term id="term-00001">modern synthesis</term>—the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s. Generally, this concept is accepted today. In short, the modern synthesis describes how evolutionary processes, such as natural selection, can affect a population’s genetic makeup, and, in turn, how this can result in the gradual evolution of populations and species. The theory also connects population change over time <term id="term-00002">(microevolution)</term>, with the processes that gave rise to new species and higher taxonomic groups with widely divergent characters, called <term id="term-00003">(macroevolution)</term>.</para><note id="fs-idp27023488" class="everyday"><label/><title>Evolution and Flu Vaccines</title>
+<para id="fs-idm26761872">People did not understand the mechanisms of inheritance, or genetics, at the time Charles Darwin and Alfred Russel Wallace were developing their idea of natural selection. This lack of knowledge was a stumbling block to understanding many aspects of evolution. The predominant (and incorrect) genetic theory of the time, blending inheritance, made it difficult to understand how natural selection might operate. Darwin and Wallace were unaware of the Austrian monk Gregor Mendel's 1866 publication "Experiments in Plant Hybridization", which came out not long after Darwin's book, <emphasis effect="italics">On the Origin of Species</emphasis>. Scholars rediscovered Mendel’s work in the early twentieth century at which time geneticists were rapidly coming to an understanding of the basics of inheritance. Initially, the newly discovered particulate nature of genes made it difficult for biologists to understand how gradual evolution could occur. However, over the next few decades scientists integrated genetics and evolution in what became known as the <term id="term-00001">modern synthesis</term>—the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s. Generally, this concept is accepted today. In short, the modern synthesis describes how evolutionary processes, such as natural selection, can affect a population’s genetic makeup, and, in turn, how this can result in the gradual evolution of populations and species. The theory also connects population change over time (<term id="term-00002">microevolution</term>), with the processes that gave rise to new species and higher taxonomic groups with widely divergent characters, called (<term id="term-00003">macroevolution</term>).</para><note id="fs-idp27023488" class="everyday"><label/><title>Evolution and Flu Vaccines</title>
 <para id="fs-idp23816096">Every fall, the media starts reporting on flu vaccinations and potential outbreaks. Scientists, health experts, and institutions determine recommendations for different parts of the population, predict optimal production and inoculation schedules, create vaccines, and set up clinics to provide inoculations. You may think of the annual flu shot as media hype, an important health protection, or just a briefly uncomfortable prick in your arm. However, do you think of it in terms of evolution?</para>
 <para id="fs-idm3795120">The media hype of annual flu shots is scientifically grounded in our understanding of evolution. Each year, scientists across the globe strive to predict the flu strains that they anticipate as most widespread and harmful in the coming year. They base this knowledge on how flu strains have evolved over time and over the past few flu seasons. Scientists then work to create the most effective vaccine to combat those selected strains. Pharmaceutical companies produce hundreds of millions of doses in a short period in order to provide vaccinations to key populations at the optimal time.</para>
 <para id="fs-idm94681808">Because viruses, like the flu, evolve very quickly (especially in evolutionary time), this poses quite a challenge. Viruses mutate and replicate at a fast rate, so the vaccine developed to protect against last year’s flu strain may not provide the protection one needs against the coming year’s strain. Evolution of these viruses means continued adaptations to ensure survival, including adaptations to survive previous vaccines.</para>