The Roots of DNA Research Focus on DNA –1869 Johann Fredrich Meischer White blood cells from salmon –1920s Alfred Mirsky Same DNA amount in all cells –1928 Frederick Griffith Pneumococci Transforming factor –1944 Oswald Avery DNA is transforming factor
The Roots of DNA Research Griffith & Avery Fig. 4.2 Transformation experiments of Griffith, A-B
The Roots of DNA Research Griffith & Avery Fig. 4.2 Transformation experiments of Griffith, C-D
The Roots of DNA Research Focus on DNA –Alfred Hershey & Barbara Chase Radiolabeled bacteriophages Determined that DNA is heritable material
The Roots of DNA Research: Hershey & Chase Fig 4.3 Determining the function of DNA
DNA to Protein 20 different amino acids Over 10,000 different proteins per microbe How does this diversity occur?
DNA to Protein The intermediary and the genetic code –DNA in nucleus, proteins made in cytoplasm –RNA present in large quantities –RNA moves from nucleus to cytoplasm –Information transfer DNA->RNA->protein –1961 Francis Crick: codons –Determination of genetic codes for each amino acid
Table 4-2: The Genetic Codes for Several Amino Acids
DNA to Protein Transcription –Promoter –mRNA –Codons –Eukaryotic mRNA Splicing: introns and exons 7-methyl guanosine cap Poly-A tail
DNA to Protein: Transcription Figure 4.7: The transcription process
DNA to Protein Translation –On ribosomes –Amino acids come together to form proteins, based on the code in the mRNA –tRNAs facitilate by “carrying” amino acids to the ribosome –Codon-anticodon interactions –Formation of peptide bonds between amino acids –Process repeats until termination –Further protein modifications after translation
DNA to Protein: Translation Figure 4.9: A summary view of protein synthesis
DNA to Protein Gene regulation –lac operon (codes for proteins that breakdown lactose) Absence of lactose –Repressor bound to operator –No transcription –No gene expression –No energy waste, making proteins required to break down lactose Presence of lactose –Lactose bound to repressor –Repressor no longer bound to operator –Transcription –Gene expression –Only now making proteins required to break down lactose
DNA to Protein: Gene Regulation Figure 4.10: The operon theory of gene regulation
Genes and Genomics Genomics –The study of genomes –1977 Frederick Sanger DNA sequencing Exact nucleotide makeup of X174.
Genes and Genomics –Effort to map the human genome –Compare E. coli (4.7 million bases) to humans (3 billion bases) –Expansion of effort Escherichia coli (bacterium) Saccharomyces cerevisiae (yeast) Caenorhabditis elegans (nematode) Drosophila melanogaster (fruitfly) Zea mays (corn) Mus musculus (mouse)
Genes and Genomics The methods of genome research –Traditional method Ordering genes on chromosomes Gene linkage map Physical map Base-by-base sequencing –“Shotgun” sequencing Fragment entire genome Sequence each base Reassemble entire genome from sequenced fragments
Genes and Genomics: Methods of genome research Figure 4.11: Sequencing methods for determining the base sequence of a molecule of DNA Traditional method
Genes and Genomics: Methods of genome research Figure 4.11: Sequencing methods for determining the base sequence of a molecule of DNA Shotgun method
Genes and Genomics Microbial genomics –1995 J. Craig Venter and Hamilton Smith Haemophilus influenzae sequence First free-living organism to be sequenced 1.8 million bases 1749 predicted genes –Mycoplasma genitalium –Methanococcus jannaschii (archaea, not bacteria) –Staphylococcus aureus –Saccharomyces cerevisiae Multiple chromosomes 12 million bases 6000 predicted genes
Genes and Genomics The human genome –Human genes number 35-50,000 (lower than 100,000 prediction) –About 3,164,700,000 bases, close to 3 billion estimate –Average gene about 3000 bases –99.9% of DNA bases are the same in most people –50% of newly discovered genes have no known function –Less than 2% of bases code for proteins –Over 50% of DNA was considered “junk” –Chromosome 1: 2968 genes (most) –Chromosome Y: 231 genes (least)
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