Chapter 14

History of the “Gene” DNA was first described in 1869 by Johannes Miescher Frederick Griffith (1928) observed harmless bacteria “transformed” into lethal ones Hereditary information must be transmitted in the molecule Hereditary material encodes information required to build a new individual Proteins and DNA were candidates. Avery MacLeod and McCarty(1944) confirmed that the “transforming principle” was a nucleic acid In the Hershey and Chase (1952) established that DNA transmits hereditary information

Nucleic acid review DNA is a polymer of nucleotides Five-carbon deoxyribose sugar Phosphate groups Nitrogen-containing base: Adenine, Thymine, Guanine, Cytosine DNA molecules can be hundreds of millions of nucleotides long DNA in a single human cell is about 2 meters long Chromosome: structure that consists of DNA and associated histone proteins

Discovering the DNA Structure 1950: Erwin Chargaff’s first rule: Amount of A equal T and G equals C second rule: Each species differs in its A to G ratios 1950s: Rosalind Franklin made x-ray diffraction image of DNA James Watson and Francis Crick propose that DNA is a double helix Two sugar–phosphate chains running in opposite directions, and paired bases inside Base pairs held by hydrogen bonds A to T G to C

Replication Cell duplicates its chromosomes by DNA replication Enzymes break the hydrogen bonds that hold the double helix together DNA polymerases attach to each strand and begin DNA synthesis The enzyme DNA ligase seals any gaps so the new DNA strands are continuous

Replication errors and repair Mistakes occur during DNA replication Replication errors may occur after a cell’s DNA gets broken or damaged DNA polymerases also proofread their work When repair mechanisms fail, an error becomes a mutation Mutations that occur during egg or sperm formation can be passed to offspring Not all mutations are deleterious

Chapter 15 Genes and Proteins

The “Central Dogma” of Biology The DNA sequence of a gene guides the assembly of an RNA or protein product Transcription and translation are part of gene expression RNA is a single-strand chain of nucleotides Unlike DNA, the sugar is a ribose and has uracil instead of thymine Messenger RNA (mRNA): specifies order of amino acid sequence Ribosomal RNA (rRNA): component of ribosomes Transfer RNA (tRNA): carries amino acids to a ribosome for protein synthesis

Transcription RNA polymerase attaches to a promoter Starts adding RNA bases G pairs with C, T pairs with A, A pairs with U (uracil) Transcription ends at the terminator

After Transcription Eukaryotic genes contain sequences called introns which are removed Remaining sequences of RNA are called exons Alternative splicing, allows exons to be rearranged into different combinations RNA also gets a guanine cap and poly-A tail

Translation mRNA’s protein-building is encoded by sets of three nucleotides called codons Translation, the codon sequence is decoded into a polypeptide of amino acids Ribosomes consists mainly of rRNA rRNA catalyzes peptide bonds between amino acids The first AUG in an mRNA: signal to start translation UAA, UAG, and UGA: signals that stop translation

Translation (cont) Translation begins in the cytoplasm when a small ribosomal subunit binds to the mRNA The anticodon of a special initiator tRNA pairs with the start codon of the mRNA Ribosome begins to assemble a polypeptide Another tRNA joins the complex pairs with the second codon The ribosome catalyzes peptide bond between first two amino acids Ribosome moves to the next codon

Chapter 16 Gene Regulation

Epigenetic Control Gene expression is controlled is response to the environment. Cells use ~10 percent of its genes at one time Only DNA that is unwound from histones are accessible to RNA polymerase. At the highest level of regulation

Transcription factors: Repressors: block promoters Activators: bring RNA polymerase to the promoter

Post-transcriptional modification can affect the form of a protein Alternative splicing RNA interference: Translation of mRNA is shut down by microRNA Post-translational modifications inhibit, activate, or stabilize proteins Many polypeptide chains must be modified before they become functional

Chapter 17

Biotechnology Gel Electrophoresis PCR Transgenics

Genome Mapping

DNA sequencing Replication occurs with added bases that stop replication (ddNTP. A mixture of strands are created each one with different terminating ddNTP Each ddNTP has fluorescent compound which is observed through gel electrophoresis