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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Outline Genes Are DNA DNA Structure DNA Replication Transcription Genetic Code Translation Gene Architecture Regulating Gene Expression Mutations

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Genes Are DNA Very early it was discovered chromosomes are composed of proteins and DNA. But it took several experiments to conclusively determine specifically which substance made up genes.  Griffith Experiment - Documented movement of genes from one organism to another (transformation).

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Genes Are DNA  Avery Experiment - Removed almost all protein from bacteria, and found no reduction in transforming activity.  Hershey-Chase - Used radioactive isotopes to label DNA and protein. Found genes used to specify new generations of viruses were made of DNA.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Genes Are DNA  Fraenkel-Conrat Experiment - Heredity properties of viruses determined by nucleic acid in core, not by protein in coat. Retroviruses - Viruses that contain RNA, causing information to flow from RNA to DNA.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Discovering DNA Structure DNA made up of nucleotides.  Central sugar, phosphate group, and an organic base. - Purines - Large bases  Adenine and Guanine - Pyrimidines - Small bases  Cytosine and Thymine  Chargaff’s Rule - A =T and G=C

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Discovering DNA Structure Watson and Crick deduced structure of DNA as a double helix. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies DNA Replication Weak hydrogen bonds between base pairs hold DNA strands together. Each chain in the helix is a complimentary mirror image of the other.  Double helix unzips and undergoes semi- conservative replication. - Confirmed by Meselson-Stahl Experiment.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies DNA Replication Helicase enzyme unwinds double helix.  Replication fork DNA polymerase reads each strand and adds nucleotides as it moves, creating a new complementary strand. DNA ligase joins the ends of new synthesized segments.  Many mechanisms exist to proofread strands and repair DNA mistakes.

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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Genes to Proteins Producing proteins from genes is known as (Central Dogma).  DNA - RNA - Protein - Gene Expression - Use of information in DNA to direct production of particular proteins.  Transcription - mRNA molecule is synthesized from gene within DNA.  Translation - mRNA used to direct protein production.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Transcription The RNA copy of a gene used to produce a protein is called messenger RNA (mRNA).  RNA polymerase binds to one strand of DNA double helix at promoter site and moves along pairing nucleotides A-U, G-C.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Genetic Code Essence of gene expression is reading information encoded within DNA and directing protein production.  Each gene is read from a fixed promoter site where RNA polymerase binds to DNA.  RNA polymerase moves down DNA in three-nucleotide steps (Codons).  Each codon corresponds to a particular amino acid possible codons

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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Translation Ribosomes use mRNA produced by transcription to direct protein synthesis.  Ribosomes composed of two subunits.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Translation Transfer (tRNA) molecules bring amino acids to the ribosome to use in making proteins.  Anticodon is the complimentary sequence to 1 of the 64 codons on the genetic code. Protein Production  Complete ribosome composed of small and large subunit bound together. - mRNA threads through producing polypeptide chain.

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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Gene Architecture In complex genes, DNA sequences encoding amino acid sequences (exons) are interrupted by extraneous nucleotides (introns). Eukaryotic cells transcribe a gene and produce a primary RNA transcript.  Enzyme complexes excise out introns and join exons to form shorter, mature, RNA that is translated into proteins.

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Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Gene Architecture Most eukaryotic genes exist in multiple copies; clusters of almost identical sequences (multigene families). Transposable sequences (transposons) are repeated hundreds of thousands of times, and move from one chromosomal location to another.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Regulating Gene Expression Many genes are turned off until needed.  Regulatory site located between promoter site and beginning edge of the gene. - When repressor is bound to regulatory site (operator), it blocks the movement of polymerase toward the gene.  Gene turned on by removing repressor.  Enhancers are located far from the gene, and bind specific regulatory proteins that help RNA polymerase find and attach to its binding site.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Regulating Gene Expression Activators bind to DNA and help unwind strands.  Cells regulate genes by binding signal molecules to activator protein. Enhancers are located far from the gene, and bind specific regulatory proteins to help RNA polymerase attach to its binding site.  Positioning at a distance permits a large number of different regulatory sequences to influence that particular gene.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Regulating Gene Expression

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Mutations A mutation is any change in the content of the genetic message.  Recombination refers to a change in position of a portion of the genetic material. - Evolution can be viewed as selection of allele combinations from a pool of alternatives. The rate of evolution is ultimately limited by the rate at which alternatives are generated.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Mutations Only mutations in the germ line can be inherited. (Somatic mutations can be passed from one cell to all its descendents).  Point Mutation - Alteration of one or a few bases. - Base substitution, insertion, or deletion.  Frame-shift mutation - Occurs when insertion or deletion throws off reading frame. Mutagen - Any substance damaging DNA.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Mutations Mutagen - Any substance damaging DNA. Transposition occurs when a particular gene moves to a different location.  May alter expression, or expression of nearby genes. - Chromosomal Rearrangement

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies

Cancer and Mutations Carcinogens - Agents believed to cause cancer.  Investigations over the last 50 years have determined many human synthetic chemicals are capable of causing cancer in laboratory animals.  Carcinogens are also mutagens.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Review Genes Are DNA DNA Structure DNA Replication Transcription Genetic Code Translation Gene Architecture Regulating Gene Expression Mutations

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