Chapter 13 Science Notes

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Chapter 13: RNA and Protein Synthesis * 13.1 RNA * The role of RNA * How does RNA differ from DNA?: There are three important differences between RNA and DNA: (1) the sugar in RNA is ribose instead of deoxyribose, (2) RNA is generally single-stranded and not double-stranded, and (3) RNA contains uracil in place of thymine * Comparing RNA and DNA: there are three differences in RNA and DNA. * Functions of RNA * Messenger RNA: type of RNA that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell * Ribosomal RNA: type of RNA that combines with proteins to form ribosomes * Transfer RNA: type of RNA that carries each amino acid to a ribosome during protein synthesis * RNA synthesis * How does the cell make RNA?: in transcription, segments of DNA serve as templates to produce complementary RNA molecules. * Transcription: synthesis of an RNA molecule from a DNA template * RNA polymerase: enzyme that links together the growing chain of RNA nucleotides during transcription using a DNA strand as a template * Promoters: specific region of a gene where RNA polymerase can bind and begin transcription * RNA editing * Introns: sequence of DNA that is not involved in coding for a protein * Exons: expressed sequence of DNA; codes for a protein * 13.2 Ribosomes and Protein Synthesis * The genetic code * What is the genetic code, and how is it read?: the genetic code is read “three” letters at a time, so that each “word” is three bases long and corresponds to a single amino acid. * Polypeptides: long chain of amino acids that makes proteins * Genetic code: collection of codons of mRNA, each of which directs the

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