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GENE EXPRESSION 13.3 (protein synthesis) Defn.: the process by which an organism’s genotype (genetic makeup) is translated into its phenotype (physical appearance). Genes Traits Proteins are made up of a particular sequence of amino acids. Genes code for the sequence of amino acids that make up proteins. Think of DNA as being a “blueprint” or recipe for making proteins. DNA works with RNA in making proteins. STRUCTURAL DIFFERENCES DNA RNA Double-Stranded Single-Stranded Sugar: deoxyribose Sugar: ribose Base Pairs: T (thymine) Base Pairs: U (uracil) Types of RNA mRNA: complementary to the DNA sequence of a gene; produced by transcription. tRNA: translates (reads) mRNA sequence into a specific sequence of amino acids; occurs during translation; has amino acids attached to it. rRNA: found in ribosomes (remember that ribosomes are organelles that make proteins). 2 Stages of Protein Synthesis (in order) Transcription: Genetic information from a strand of DNA is copied into a strand of mRNA; “copying notes from the board to your notebook”. Translation: process in which the “language” of nucleic acids (bases) is changed into the “language” of proteins (amino acids); mRNA amino acids proteins. TRANSCRIPTION RNA polymerase (an enzyme) “unzips” a section of the DNA strand ….breaks the hydrogen bonds holding the nitrogenous bases together (the “steps” of the ladder) at the promoter site. Unattached RNA (free) nucleotides bind to their complimentary bases on the DNA strand to form a molecule of mRNA (messenger RNA); RNA polymerase works like a “train moving down the tracks”. This process repeats until DNA signals to STOP! The stop signal marks the end of each gene. mRNA then moves out of the nucleus into the cytoplasm and attaches to a ribosome proteins begin being made. TRANSLATION Codon: a 3 base section of mRNA ex. ATC…__ __ __ * this is how tRNA (transfer RNA) delivers the amino acids in the correct order. * codons carry a code for a specific amino acids. TRANSLATION (cont.) Anticodon: a sequence of 3 bases found on tRNA. * each tRNA carries only 1 anticodon which complements a specific mRNA codon. * what is the tRNA anticodon for the mRNA codon GCA? * what is the tRNA anticodon for the mRNA codon GCU? http://users.rcn.com/jkimball.ma.ultranet/Bi ologyPages/T/Translation.html http://www.wisconline.com/objects/index_tj.asp?objID=AP 1302