Nucleotide Triplets:

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  • Topic: DNA, RNA, Ribosome
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  • Published : January 2, 2006
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A portion of a specific DNA molecule consists of the following sequence of nucleotide triplets:

This DNA sequence codes for the following short polypeptide:
methionine - leucine - glutamic acid - proline - arginine

Describe the steps in the synthesis of this polypeptide. What would be the
effect of a deleltion or an addition in one of the DNA nucleotides? What would
be the effect of a substitution in one of the nucleotides?


In the transcription phase of protein synthesis, students were given a point for a correct definition of transcription. They were awarded one point for mentioning each of the following:
__ DNA as the template molecule for messenger RNA
__ The proper base pairing (including the uracil substitution) __ The chemical characteristics of nucleotides
__ A comparison of RNA and DNA (other than uracil substitution) __ The triplet arrangement of codons and/or anticodons
__ The control of transcription (Operon, etc.)
__ Promoters
__ The role of polymerase
__ Intervening sequences in eukaryotic cells
__ Factors involved in the release of mRNA from DNA
__ 5' - 3' arrangement with attachment at -OH end
A definition of translation was worth an additional point with one point given for mention of each of the following:
__ Movement of mRNA from nucleus to ribosome
__ Association of mRNA with the ribosome and ribosomal RNA __ Location of ribosomes
__ Description of ribosome/polyribosome structure
__ Role of transfer RNA in transporting amino acids
__ Specific characteristics of tRNA
__ Amino acid-tRNA complex activation
__ Role of ATP and enzymes
__ tRNA initiator molecules (met or f-met)
__ Initiation factors (GTP, etc.) resulting in union of 30s and 50s __ Bonding of tRNA to 50s (A site)
__ Role of amino transferase
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