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1 Biology 1107 Lecture #35 04-07-10 . Outline of today’s lecture: Chapter 17 1. The structure of RNA 2. The dictionary of the genetic code 13. Transcription - the DNA-directed synthesis of RNA 4. Eukaryotic RNA processing 5'cap and poly(A) tail RNA splicing 5. Translation (protein synthesis) transfer RNA ribosomes initiation elongation termination 6. Polysomes Begin chapter 17 from gene to protein. . ..... Basic idea. ... DNA -> RNA -> Protein. The specific sequences of nucleotides along the DNA strands is a code for the sequence of amino acids in the primary structure of proteins. Genes provide the instructions for making specific proteins. The bridge between DNA and protein synthesis is RNA. 3. The structure of RNA What is the difference between DNA and 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 a protein, 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. This process is used to synthesize any type of RNA from a DNA template. Transcription of a gene produces a messenger RNA ( mRNA ) molecule. During translation , the information contained in the order of nucleotides in mRNA is used to determine the amino acid sequence of a polypeptide. Translation occurs at ribosomes. The basic mechanics of transcription and translation are similar in eukaryotes and prokaryotes. Because bacteria lack nuclei, transcription and translation are coupled. Ribosomes attach to the leading end of a mRNA molecule while transcription is still in progress.
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In a eukaryotic cell, almost all transcription occurs in the nucleus and translation occurs mainly at ribosomes in the cytoplasm. In addition, before the primary transcript can leave the nucleus it is modified in various ways during RNA processing before the finished mRNA is exported to the cytoplasm. To summarize, genes program protein synthesis via genetic messenger RNA. The molecular chain of command in a cell is: DNA -> RNA -> protein. 4. The dictionary of the genetic code Look at figure 17.5 The dictionary of the genetic code. In the genetic code, nucleotide triplets of RNA specify amino acids If the genetic code consisted of a single nucleotide or even pairs of nucleotides per amino acid, there would not be enough combinations (4 and 16 respectively) to code for all 20 amino acids. Triplets of nucleotide bases are the smallest units of uniform length that can code for all the
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This note was uploaded on 10/12/2010 for the course BIO 3453 taught by Professor Dervartarian during the Spring '09 term at UGA.

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