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Download The Blueprint of Life, From DNA to Protein
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From DNA to Protein Chapter 8 Terminology • Genetics • Genome • Chromosome • Gene • Locus • Alleles • Genotype/Phenotype • Heredity • Living cells must accomplish two general tasks to multiply and survive – DNA replication – Gene expression • Expression involves two process – Transcription – Translation – Flow of information from DNA to RNA to protein DNA • Polymer of nucleotides • Hydrogen bonds between complementary bases – AT and CG • Antiparallel • New nucleotides can only be added to the “free” 3’ end DNA synthesis involves anabolic polymerization Monomers (Triphosphate deoxyribonucleotides) provide required energy for DNA synthesis Replication produces two DNA double helixes Each contains one original strand and one new strand One DNA double helix. Semi-conservative DNA replication Two identical DNA double helixes, each with one parental strand (blue) and one new strand (pink). • DNA replication in bacteria is bi-directional – due to closed circular chromosome – replication forks eventually meet and two complete loops are separated • Bacterial DNA is attached at several points to the cell membrane – Enzymes need for replication are membrane proteins • Topoisomerase (DNA gyrase) • Helicase • Primase • DNA polymerases • DNA Ligase • Bacteria replication involves methylation of daughter stands – Methylase – Adds methyl group (-CH3) to nitrogenous bases (typically adenine) • Methylation functions: – Initiation of DNA repliction – Control of genetic expression – Protection from viral infection – Repair of DNA DNA Replication • As DNA unwinds, it creates a replication fork • As nucleotides are added, the replication fork moves down the parental strand – Leading strand • Is synthesized CONTINUOUSLY as the DNA polymerase moves towards the replication fork – Lagging strand • Is synthesized DISCONTINUOUSLY in pieces as DNA polymerase moves away from the replication fork • Okazaki fragments Single Strand Binding Proteins • DNA contains the instructions for protein synthesis – Genes • RNA carries out the instructions • Genetic information flows from DNA to RNA to protein • Central Dogma of Molecular Biology – DNA – RNA Transcribed Translated RNA Protein Gene Expression • Transcription – RNA polymerase synthesizes complementary mRNA from DNA template – Cytoplasm of prokaryotes and the nucleus of eukaryotes Concurrent RNA transcription Multiple copies of RNA can be transcribed simultaneously • Eukaryotic DNA is more complex – Requires posttranscriptional modifications – Spliceosome – Cap and tail • Translation – The language of mRNA is in the form of codons • Three nucleotides situated next to each other on DNA – Sequence of codons determines sequence of amino acids in the protein – 64 codons make up the “alphabet” • 61 are sense codons • 3 “stop codons” •The site of translation is the ribosome • tRNA brings appropriate amino acid to site of translation • Each tRNA has an anticodon – complementary sequence to the mRNA codon In a prokaryotes, many molecules of mRNA can by transcribed simultaneously Why can translation begin before transcription is completed in a prokaryote but not in a eukaryote? gene DNA complementary DNA strand template DNA strand codons mRNA anticodons tRNA amino acids protein methionine glycine valine