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chap17studyguide - Chapter 17 From Gene to Protein Study...

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Chapter 17 From Gene to Protein Study Guide Overview: The Flow of Genetic Information The information content of DNA is in the form of specific sequences of nucleotides along the DNA strands. The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. Gene expression, the process by which DNA directs protein synthesis, includes two stages called transcription and translation. Proteins are the links between genotype and phenotype. ° For example, Mendel’s dwarf pea plants lack a functioning copy of the gene that specifies the synthesis of a key protein, gibberellin. ° Gibberellins stimulate the normal elongation of stems. Concept 17.1 Genes specify proteins via transcription and translation Transcription and translation are the two main processes linking gene to protein. Genes provide the instructions for making specific proteins. The bridge between DNA and protein synthesis is the nucleic acid RNA. RNA is chemically similar to DNA, except that it contains ribose as its sugar and substitutes the nitrogenous base uracil for thymine. ° An RNA molecule almost always consists of a single strand. In DNA or RNA, the four nucleotide monomers act like the letters of the alphabet to communicate information. The specific sequence of hundreds or thousands of nucleotides in each gene carries the information for the primary structure of proteins, the linear order of the 20 possible amino acids. To get from DNA, written in one chemical language, to protein, written in another, requires two major stages: transcription and translation. During transcription, a DNA strand provides a template for the synthesis of a complementary RNA strand. ° Just as a DNA strand provides a template for the synthesis of each new complementary strand during DNA replication, it provides a template for assembling a sequence of RNA nucleotides.
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Transcription of many genes produces a messenger RNA (mRNA) molecule. During translation, there is a change of language. ° The site of translation is the ribosome, complex particles that facilitate the orderly assembly of amino acids into polypeptide chains. Why can’t proteins be translated directly from DNA? ° The use of an RNA intermediate provides protection for DNA and its genetic information. ° Using an RNA intermediate allows more copies of a protein to be made simultaneously, since many RNA transcripts can be made from one gene. Also, each gene transcript can be translated repeatedly. The basic mechanics of transcription and translation are similar in eukaryotes and prokaryotes. Because bacteria lack nuclei, their DNA is not segregated from ribosomes and other protein-synthesizing equipment.
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