Gene regulation in prokaryotes

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  • 1. DNA Replication & Expression DNA – carries genetic information a polymer . . . . . . made of ______________________________ What is a polymer? The Basic structure of a nucleotide: RNA – involved in translating genetic code a polymer . . . . . . made of 4 different nucleotides What are two differences between RNA and DNA nucleotides? DNA forms a double helix Who discovered this? 1
  • 2. sugar-phosphate “backbone” nucleotide “rungs” sketch the basic structure  Involves the Precise pairing of nucleotides - what are the two pairings? - strands are held together by ________________ DNA Replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” – Watson & Crick 1. Strands separate 2. Each strand serves as template for a new strand A pairs with ___ G pairs with ___ Replication occurs at many sites simultaneously & involves 3 enzymes Sketch the process & describe the function of each enzyme 2
  • 3. What does it mean to say that replication is semiconservative? The Gene What is a gene? How many genes are in the human genome? How do we know? What determines an individual’s phenotype? The Genetic Code Problem: polymer made up of 4 nucleotides (DNA) must be translated into a polymer made up of 20 amino acids (protein) Solution: • specify one amino acid examples: “DNA codon” amino acid T-C-T Arginine A-C-C Tryptophane A-T-G Tyrosine 3
  • 4. What do we mean by saying that the Genetic Code is arbitrary . . . . . . and universal What are the evolutionary implications of this? Why would it be impossible for humans to mate with aliens? 4
  • 5. Gene Expression Where, the sequence of nucleotides in a gene … TCTACCATG specify a sequence of amino acids … Overview of Gene Expression: Transcription in detail TACGCCTA What is the promoter region? What is its function? Why is the enzyme called RNA polymerase? 5
  • 6. Where does transcription take place? Why? Judging from the photograph, how many mRNA’s can be made from one gene at a time? Translation: mRNA  protein Three things needed to make a protein: • • • Riobosomes Function: Location: Structure: 6
  • 7. Transfer RNA (tRNA) Why does Dr. Gendron liken tRNA to the Rosetta Stone? Where is the synthesis of proteins carried out? 7
  • 8. Mutations What is a mutation? 1. Chromosomal Mutations The 2 types of chromosomal mutation and examples of each: 2. Point Mutations: Changes in the DNA sequence When are these most likely to occur? a. Substitution Tyrosine – Alanine - Leucine TACGCCCTA 8
  • 9. b. Deletions & Insertions are examples of _________________________ why are they called that? THE FAT CAT ATE THE SAD RAT What causes mutations? 1. 2. mutagenic factors a. b. c. Consequences of Mutation 1. Harmful which is more likely to be harmful – a simple substitution or a frame- shift? WHY? 9
  • 10. 2. Neutral How can a mutation be neutral (i.e. be neither harmful or beneficial)? How can the accumulation of neutral mutations be used as an evolutionary clock? 3. Beneficial Final Points • Why are mutations necessary for evolution to occur? What determines if a mutation will be passed on to your offspring? 10
  • 11. Viral Genetics Living or not? WHY? • Viruses parasitize a host cell • Genetic Material of Viruses • Basic Structure of Viruses Virus Life Cycle Retroviruses 11
  • 12. Influenza Virus The current avian flu virus (H5N1) is the most virulent form ever recorded Cases Death Mortality Dec 03 – Mar 04 35 24 69% Apr 04 – Oct 04 9 8 89% Dec 04 – Nov 05 78 30 38% How the Avian Flu virus could become more dangerous: In February 2004, avian influenza virus was detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. In May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported ("swine flu"). Along with the continuing pattern of virus circulation in poultry, the occurrence in swine raises the level of concern about the possible evolution of the virus into a strain capable of causing a global human influenza pandemic. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment.) with the avian virus, swap genes and mutate into a form which can pass easily among humans. 12
  • 13. Gene Regulation What is Differentiation? How do cells become different? What is evidence for differential expression of genes during differentiation? • • Gene regulation in prokaryotes A generalized metabolic pathway: substrate product G1 G2 G3 There are two possible control mechanisms 1. genes are normally “off” - turned “on” by ________________ 2. genes are normally “on” - turned “off” by ________________ 13
  • 14. Lactose metabolism in E. coli G1 G2 G3 Lactose product To summarize, the lac genes - normally turned off by repressor molecule (in absence of lactose) - repressor inactivated by lactose (the substrate of the metabolic pathway above) Gene Regulation in Humans (& other eukaryotes) There are different levels of control in eukaryotes 1. Regulatory proteins 2. Gene packing can be used to disable genes What is it? - packed genes are not accessible to RNA polymerase 14
  • 15. In females one X chromosome is permanently disabled by packing 3. Introns may play a role in gene expression Introns – “nonsense” code Exons – usable code How does the cell deal with these non-coding regions Cell metabolism is also be regulated at the level of the protein mRNA Inactive Protein Active Protein Amino Acids 15
  • 16. Genetics in the 21st Century Scientific knowledge tends to grow exponentially and Genetics is one of the most active fields The Human Genome Project • ~______________________ genes • Function unknown for 50% of genes • ______% identical in all people • ______% "Junk DNA" Genetic Engineering Genetic engineering, in a sense, has been around for a long time Today genetic engineering often involves recombinant DNA what is it? recombinant DNA occurs naturally and artificially 16
  • 17. How are genetically modified organisms (GMO’s) most often used in agriculture? How is genetic engineering used in medicine? What are its potential uses? Forensic use of Biotechnology What is the primary use of biotechnology in forensics? Cloning cloning of genes vs. cloning of individuals reproductive cloning vs. therapeutic cloning 17