The Genetic Code Genetic code: the dictionary of molecular ...

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    26-May-2015

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<ul><li> 1. The Genetic Code</li></ul> <p> 2. Genetic code: the dictionary of molecular meaning </p> <ul><li>Universal:same code used by all organisms on earth </li></ul> <ul><li>Triplet: 3 bases = one word </li></ul> <ul><li>Unambiguous:each triplet has only one meaning </li></ul> <ul><li>Degenerate:individual amino acids may be called for by more than one triplet (this is also referred to as redundant) </li></ul> <p> 3. </p> <ul><li>Puntuationless: no spaces between words</li></ul> <ul><li>Colinear:sequence in mRNA is perfectly compatible with amino acid sequence in finished protein </li></ul> <ul><li>Specific signnals </li></ul> <ul><li><ul><li> Start = AUG </li></ul></li></ul> <ul><li><ul><li> Stop = UAA, UAG, and UGA </li></ul></li></ul> <p> 4. </p> <ul><li>During transcription, one DNA strand, thetemplate strand , provides a template for ordering the sequence of nucleotides in an RNA transcript. </li></ul> <ul><li><ul><li>The complementary RNAmolecule is synthesizedaccording to base-pairingrules, except that uracil isthe complementary baseto adenine. </li></ul></li></ul> <ul><li>During translation, blocksof three nucleotides,codons , are decoded intoa sequence of amino acids.</li></ul> <p>Fig. 17.3 5. </p> <ul><li>By the mid-1960s the entire code was deciphered. </li></ul> <ul><li><ul><li>61 of 64 triplets codefor amino acids.</li></ul></li></ul> <ul><li><ul><li>The codon AUG notonly codes for theamino acid methioninebut also indicates thestart of translation. </li></ul></li></ul> <ul><li><ul><li>Three codons donot indicate aminoacids but signalthe terminationof translation. </li></ul></li></ul> <p>Fig. 17.4 6. </p> <ul><li>To extract the message from the genetic code requires specifying the correct starting point. </li></ul> <ul><li><ul><li>This establishes thereading frameand subsequent codons are read in groups of three nucleotides. </li></ul></li></ul> <ul><li><ul><li>The cells protein-synthesizing machinery reads the message as a series of nonoverlapping three-letter words. </li></ul></li></ul> <p> 7. What Does DNA Say? </p> <ul><li>Coding strand: provides info for the template strand </li></ul> <ul><li>Template strand: provides the template for mRNA </li></ul> <ul><li>Template strand is read 3 -&gt;5 </li></ul> <ul><li>mRNA is made 5-&gt;3 </li></ul> <ul><li>Amino acids are coded for on themRNA!! </li></ul> <p> 8. Steps </p> <ul><li>Write template DNA strand from coding strand (it is complementary) </li></ul> <ul><li>mRNA is complementary to template DNA strand (remember U intead of T) </li></ul> <ul><li>tRNA strand is complementary to mRNA </li></ul> <ul><li>Use mRNA to get amino acids </li></ul> <ul><li>Start means start and stop means stop </li></ul>

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