Lec 2 DNA - Lecture Overview DNA Structure Replication...

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Lecture Overview – DNA •S t ru c tu re • Replication – Protein Synthesis • Types of RNA • Transcription
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Structure of Nucleotides in DNA • Each nucleotide consists of – Deoxyribose (5-carbon sugar) – Phosphate group – A nitrogen-containing base • Four bases – Adenine, Guanine, Thymine, Cytosine
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Nucleotide Bases phosphate group deoxyribose ADENINE (A) THYMINE (T) CYTOSINE (C) GUANINE (G)
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Composition of DNA • Erwin Chargaff: A=T and G=C Erwin Chargaff 1905-2002, ca. 1930
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Rosalind Franklin’s Work • Was an expert in x-ray crystallography • Used this technique to examine DNA • Concluded that DNA was some sort of helix • Phosphate bonds were on the outside of the molecule Rosalind Franklin 1920-1958, ca. 1950
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Watson-Crick Model • DNA consists of two nucleotide strands – Molecule is a double helix • Strands run in opposite directions – antiparallel • Strands are held together by hydrogen bonds between bases
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DNA Structure Helps Explain How it Duplicates • DNA is two nucleotide strands held together by hydrogen bonds • Hydrogen bonds between two strands are easily broken • Each single strand then serves as template for new strand
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DNA Replication new new old old • Each parent strand remains intact •E v e r y D N A molecule is half “old” and half “new” http://www.youtube.com/watch?v=hfZ8o9D1tus &feature=related
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Each old strand serves as the template for complementary new strand - “Semiconservative”
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Same two steps produce ALL proteins: 1) DNA is transcribed to form RNA – Occurs in the nucleus – RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains – Occurs at the ribosome Steps from DNA to Proteins
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Three Classes of RNAs • Messenger RNA (mRNA) – Carries protein-building instruction • Ribosomal RNA (rRNA) – Major component of ribosomes • Transfer RNA (tRNA) – Delivers amino acids to ribosomes
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A Nucleotide Subunit of RNA sugar (ribose) phosphate group uracil (base)
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Base Pairing During Transcription • A new RNA strand can be put together on a DNA region • C pairs with G • Uracil (U) pairs with adenine (A) •N o t h y m i n e
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• Like DNA replication – Nucleotides added in 5’ to 3’ direction • Unlike DNA replication – Only small stretch is template – RNA polymerase catalyzes nucleotide addition – Product is a single strand of RNA
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How does transcription begin? With a "Promoter”
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Lec 2 DNA - Lecture Overview DNA Structure Replication...

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