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Genetics After Mendel: Discovering the Chemical Nature of Genes

Explore the journey of genetics after Mendel and learn about the discovery of the chemical nature of genes. From Mendel's traits to Watson and Crick's double helix model, unravel the mysteries of DNA replication, transcription, and translation. Understand how DNA controls the cell and discover the role of nucleic acid sequencing in analyzing genes.

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Genetics After Mendel: Discovering the Chemical Nature of Genes

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  1. Sample exam is available at http://www.bio200.buffalo.edu No answers are available

  2. Genetics After Mendel Get your clickersready

  3. Evidence from Biochemistry The chemical nature of genes is discovered

  4. What is a Gene? • 1866 Mendel = Traits are determined by particles (factors) that are passed from one generation to the next. • 1909 Danish Botanist Wilhelm Johanssen • Coins word “gene” for the unit associated with an inherited trait

  5. What is a Gene? • 1910 Thomas Morgan work on fruit flies shows that genes sit on chromosomes • 1941 George Beadle & Edward Tatum introduce idea that “One gene makes one enzyme.”

  6. What is a Gene? • 1944 Avery, MacLeod & McCarty find • Genes are made of DNA • 1953 Watson & Crick publish structure of DNA;

  7. What is the chemical nature of DNA?

  8. Double Helix Model James Watson & Francis Crick

  9. Another model of DNA Two strands of DNA connected together by hydrogen bonds between the base units Guanine = G Cytosine= C Adenine = A Thymine = T Double Helix

  10. Genes Are Composed of Nucleic Acids (DNA) • Double Helix Model Base units: Guanine = G Cytosine = C Adenine = A Thymine = T

  11. Two basic questions about DNA • How does it make copies of itself before cell division? • How does it control the cell?

  12. DNA Replication Solved • When cells divide they must make a copy of the DNA sequence. • Suppose the double helix reads this way: GGCTCAAATGTTAAAAGGTCATGGACCGTAT.. CCGAGTTTACAAT TTTCCAGTACCTGGCATA

  13. DNA Replication First the strands unzip GGCTCAAATGTTAAAAGGTCATGGACCGTAT.. CCGAGTTTACAAT TTT CCAGT ACCTGGCATA

  14. DNA Replication • Then each separate strand makes a complementary copy of itself. GGCTCAAATGTTAAAAGGTCATGGACCGTAT...CCGA G T

  15. DNA Replication • SO GGCTCAAATGTTAAAAGGTCATGGACCGTAT... Makes this GGCTCAAATGTTAAAAGGTCATGGACCGTAT…… CCGAGTTT ACAATTTTCCAGTACCT GGCATA…..

  16. DNA Replication CCGAGTTT ACAATTTTCCAGTACCT GGCATA…..GGCTCAAATGTTAAAAGGTCATGGACCGTAT…… Makes this CCGAGTTT ACAATTTTCCAGTACCT GGCATA….. AND THIS

  17. DNA Replication • We end up with two double strands CCGAGTTT ACAATTTTCCAGTACCT GGCATA…..GGCTCAAATGTTAAAAGGTCATGGACCGTAT…… GGCTCAAATGTTAAAAGGTCATGGACCGTAT… CCGAGTTT ACAATTTTCCAGTACCT GGCATA…

  18. How DNA controls the cell is solved

  19. How does DNA control the cell? DNA mRNA Protein

  20. Central Dogma of Molecular Biology DNA Transcription mRNA Translation Protein

  21. Where does this happen? DNA In the nucleus In the cytoplasm’s ribosomes mRNA Transcription Protein Translation

  22. Instructions from the DNA mRNA Ribosome tRNA Amino acids as raw material Links amino acids together to make protein

  23. Albinism = Complete dominance Normal skin = AA or Aa Albinos = aa How do we reconcile the DNA model with Mendelian Genetics?

  24. Albinism Enough enzyme to do the job

  25. Not Enough enzyme to do the job

  26. Two different hemoglobin molecules are coded: Normal and Sickle i.e. two different proteins made

  27. The Code ?What determines the kind of protein made? • A set of 3 nucleotide bases in DNA (triplets) determines which amino acid will be used to put into the protein. GGAATATCCCCTTAGGGAAGCCCTTCGAATCCT…. DNA Triplets

  28. What determines the kind of protein made? DNA Triplets GGAATATCCCCTTAGGGAAGCCCTTCGAATCCT.. CCUUAUAGGGGAAUCCCUUCGGGAAGCUUAGGA... RNA Codons Protein

  29. Triplets & Codons How many bases are needed to code for 20 amino acids? (There are only 4 to use) How about 2? 42 = only 16. Not enough How about 3 bases? 43 = 64 DNA triplets More than enough. We only need 20 different DNA triplets ! and 20 RNA codons

  30. RNA Codons G C U G C C G C A G C G

  31. What will be aDNA code foraspartic acid? DNA CTA or CTG mRNA GAU or GAC Amino Asparic acid Acid

  32. RNA Codons Several codons code for the same amino acid e.g. phenylalanine is coded by: UUU UUC e.g. leucine is coded by: UUA UUG CUU CUC CUA CUG

  33. RNA Codons The same messenger RNA codons are used in virtually all organisms !

  34. So? What is a Gene? • A gene is a sequence of nucleotide bases that code for a polypeptide. • CTCAAATGTTAAAAGGTCATGGACCGTAT……. • The order of the nucleotide bases determines which amino acid is put into the polypeptide.

  35. Protein Analysis • Amino Acid sequencing e.g. Cytochrome C enzyme (104 amino acids) Human vs. rhesus monkey 1 difference Human vs. dog 11 Human vs. rattlesnake 14 Human vs. bullfrog 18 Human vs. tuna fish 21 Human vs. fruit fly 29 Human vs. pumpkin 36 Human vs. bacteria 56

  36. Nucleic Acid Sequencing (DNA & RNA) Ultimate method Can analyze nuclear or non-nuclear DNA (mitochondria, chloroplasts or plasmids) • Complete genome sequences now known for some viruses, s. bacteria, a nematode worm, rat, chimpanzee, humans, etc.

  37. 99.9% of the genes in all humans are the same.

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