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Lecture 7

A summary of the Lecture 7 readings complete with diagrams.

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John Coleman

Lecture 7 Notes Chapter 6: How Cells read the Genome: From DNA to Protein When the cell needs a particular protein, the nucleotide sequence of the appropriate portion of the DNA is first copied into RNA transcription. It is these RNA copies of segments of the DNA that are used directly as templates to direct the synthesis of the protein translation The flow of genetic information in cells is therefore from DNA to RNA to protein. All cells express their genetic information in this waya fundamental principle called the central dogma of molecular biology. Portions of DNA Sequence Are Transcribed into RNA Like DNA, RNA is a linear polymer made of four different types of nucleotide subunits linked together by phosphodiester bonds. It differs from DNA chemically in two respects: 1. The nucleotides in RNA are ribonucleotidesthat is, they contain the sugar ribose rather than deoxyribose 2. Although, like DNA, RNA contains the bases adenine (A), guanine (G), and cytosine (C), it contains the base uracil (U) instead of the thymine (T) in DNA. Since U, like T, can base-pair by h- bonding with A 3. DNA is a ds-helical molecule, whereas RNA is ss (but can fold into a ds shape) Transcription Produces RNA Complementary to One Strand of DNA Transcription begins with the opening and unwinding of a small portion of the DNA double helix to expose the bases on each DNA strand, where one strand behaves as a template The nucleotide sequence of the RNA chain is determined by the complementary base-pairing between incoming nucleotides and the DNA template. When a good match is made, the incoming ribonucleotide is covalently linked to the growing RNA chain in an enzymatically catalyzed reaction. The RNA chain produced by transcriptionthe transcriptis therefore elongated one nucleotide at a time o Its nucleotide sequence is exactly complementary to the strand of DNA used as the template
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