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The discovery of DNA as genetic information was a long time coming

The discovery of DNA as genetic information was a long time coming Early 1900s- chromosomes contained genetic information what was it- the DNA or the proteins? 1928- the Griffiths experiment genetic information could be transferred from one organism to another

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The discovery of DNA as genetic information was a long time coming

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  1. The discovery of DNA as genetic information was a long time coming Early 1900s- chromosomes contained genetic information what was it- the DNA or the proteins? 1928- the Griffiths experiment genetic information could be transferred from one organism to another 1953- structure of DNA solved

  2. DNA structure Chargaff: same amount of A as T, and C as G Franklin and Wilkins: DNA is a double helix (Franklin: sugar-phosphate backbone) 1953- Watson and Crick put all of this information together and deduced the structure

  3. Purines are bulkier than pyrimidines Adenine (purine) pairs with thymine (pyrimidine) Guanine (purine) pairs with cytosine (pyrimidine) Explained by Chargaff’s rule If an organism’s DNA is 10% adenine, you know the concentrations of all the other nucleotides!

  4. Watson and Crick: this explains how DNA must replicate One strand is complementary to the other Meselson and Stahl: proved DNA replication is “semiconservative” Original molecule is double-stranded each new molecule contains one old strand and one new strand

  5. DNA replication Occurs during S phase Many enzymes involved; principal ones are: DNA polymerase Helicase Ligase

  6. Transcription Gene expression – how information gets from DNA to form a protein. Two stages: Transcription- synthesis of messenger RNA Translation- mRNA directs protein synthesis

  7. In eukaryotes, the transcript must be edited Introns- DNA sequences that are edited out Exons- the sequences that actually make up the gene

  8. Control of transcription Which genes are transcribed and how often Promoters Enhancers In bacteria, a group of genes may function as an operon

  9. SECOND BASE U C A G G U C A G UUU UUC UUA UUG UCU UCC UCA UCG UAU UAC UAA UAG UGU UGC UGA UGG Phe Leu Tyr Cys Ser Pro Thr Ala U Stop Stop Stop Trp CUU CUC CUA CUG U C A G CCU CCC CCA CCG CGU CGC CGA CGG CAU CAC CAA CAG His Gln C Leu Arg THIRD BASE FIRST BASE AUU AUC AUA AUG U C A G ACU ACC ACA ACG AAU AAC AAA AAG AGU AGC AGA AGG Asn Lys Ser Arg A Ile Met Val U C A G GCU GCC GCA GCG GAU GAC GAA GAG GGU GGC GGA GGG GUU GUC GUA GUG Asp Glu G Gly

  10. Which type of mutation will tend to have a greater impact on protein function? Why? Frameshift, because all of the amino acids “downstream” from the mutation will be affected. What are the consequences of gene mutation? New alleles, (genetic diversity: no apparent effect or visible but insignificant difference such as free or attached earlobes) Loss of protein function (disease, e.g., PKU, sickle cell anemia) Loss of viability (death)

  11. Recombination: portions of chromosomes are rearranged Genes are moved “out of position” inversions (ABCDACBD) duplications (ABCDABBCD) translocations (ABCDEFABCJKL (GHIJKLGHIDEF)   Effects can be drastic (and permanent)

  12. What kind of cell is affected and what Are the consequences? Germ-line cell (gamete) these mutations are inherited these give rise to alleles Somatic cell these affect the particular tissue but cannot be inherited example: tumors Implications for gene therapy

  13. How do mutations happen? Spontaneous errors of replication Chemicals (“mutagens”) Radiation Viruses If damage to DNA is not repaired, the mutation becomes incorporated into the genome.

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