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Molecular Genetics ( from DNA to Trait )

Molecular Genetics ( from DNA to Trait ). Double helix structure of DNA. “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick. Directionality of DNA. nucleotide.

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Molecular Genetics ( from DNA to Trait )

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  1. Molecular Genetics (from DNA to Trait)

  2. Double helix structure of DNA “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick

  3. Directionality of DNA nucleotide • You need to number the carbons! • it matters! PO4 N base CH2 5 This will beIMPORTANT!! O 1 4 ribose 3 2 OH

  4. Anti-parallel strands • Nucleotides in DNA backbone are bonded from phosphate to sugar between 3 & 5 carbons • DNA molecule has “direction” • complementary strand runs in opposite direction 5 3 3 5

  5. Base pairing in DNA • Purines • adenine (A) • guanine (G) • Pyrimidines • thymine (T) • cytosine (C) • Pairing • A : T • 2 bonds • C : G • 3 bonds

  6. Copying DNA • Replication of DNA • base pairing allows each strand to serve as a template for a new strand • new strand is 1/2 parent template & 1/2 new DNA

  7. Replication: 1st step • Unwind DNA • helicase enzyme • unwinds part of DNA helix • stabilized by single-stranded binding proteins helicase single-stranded binding proteins replication fork

  8. Replication: 2nd step • Build daughter DNA strand • add new complementary bases • DNA polymerase III But… We’re missing something! What? Where’s theENERGYfor the bonding! DNA Polymerase III

  9. 3 5 Replication energy DNA Polymerase III • Adding bases • can only add nucleotides to 3 end of a growing DNA strand • need a “starter” nucleotide to bond to • strand only grows 53 DNA Polymerase III energy DNA Polymerase III energy DNA Polymerase III energy B.Y.O. ENERGY! The energy rulesthe process 3 5

  10. Editing & proofreading DNA • 1000 bases/second = lots of typos! • DNA polymerase I • proofreads & corrects typos • repairs mismatched bases • removes abnormal bases • repairs damage throughout life • reduces error rate from 1 in 10,000 to 1 in 100 million bases

  11. Fast & accurate! • It takes E. coli <1 hour to copy 5 million base pairs in its single chromosome • divide to form 2 identical daughter cells • Human cell copies its 6 billion bases & divide into daughter cells in only few hours • remarkably accurate • only ~1 error per 100 million bases • ~30 errors per cell cycle

  12. The “Central Dogma” • Flow of genetic information in a cell • How do we move information from DNA to proteins? transcription translation RNA DNA protein trait replication

  13. RNA • ribose sugar • N-bases • uracil instead of thymine • U : A • C : G • single stranded

  14. There are Different RNAs with Distinct Functions

  15. Transcription makes an RNA copy of DNA fromDNA nucleic acid languagetoRNA nucleic acid language

  16. RNA polymerase acts here Transcription The enzyme RNA polymerase opens the DNA strands and synthesizes an RNA complementary to only one of the DNA strands.

  17. Transcription • Making mRNA • transcribed DNA strand = template strand • untranscribed DNA strand = coding strand • same sequence as RNA • synthesis of complementary RNA strand • transcription bubble • enzyme • RNA polymerase coding strand 3 A G C A T C G T 5 A G A A A C G T T T T C A T C G A C T DNA 3 C T G A 5 A T G G C A U C G U T C unwinding 3 G T A G C A rewinding mRNA template strand RNA polymerase 5 build RNA 53

  18. Eukaryotic Genes are Segmented link Genes are made of parts represented in the mRNA (exons) and parts that are transcribed but not present in the mRNA (introns). Introns are removed from the primary transcript and exons are spliced together to make mRNA. In some genes more than 90% of the pre-mRNA is destroyed, never to appear in the mRNA.

  19. Translation in Eukaryotes

  20. Triplet Code • Codons • blocks of 3 nucleotides decoded into the sequence of amino acids

  21. DNA code  mRNA (copied code)  gives amino acid sequence tRNA gets amino acids  ribosomes assembles polypeptide  chains make up proteins…

  22. The Cryptogram of LIFE These are the words of the genetic language.

  23. tRNA • An adaptor • Couples codons and anticodons • Amino Acids in proper order as per DNA

  24. E P A

  25. RNA polymerase DNA Can you tell the story? Review aminoacids exon intron tRNA pre-mRNA 5' cap mature mRNA aminoacyl tRNAsynthetase polyA tail 3' large ribosomal subunit polypeptide 5' tRNA small ribosomal subunit E P A ribosome

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