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DNA and biotechnology

DNA and biotechnology. What is DNA?. “Structure and function”: molecules are put together in a way so that their structure contributes to their function DNA is a very long, thin molecule Double helix Over 5 feet long when stretched out Contains genetic information Stored in nucleus.

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DNA and biotechnology

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  1. DNA and biotechnology

  2. What is DNA? • “Structure and function”: molecules are put together in a way so that their structure contributes to their function • DNA is a very long, thin molecule • Double helix • Over 5 feet long when stretched out • Contains genetic information • Stored in nucleus

  3. Structure of DNA • Why double helix? • Two strands of nucleotides • “Base-pairing rules” • A-T; C-G • Fits into nucleus • Can be accurately copied when cell divides • Very stable

  4. Accurate copying is extremely important • Semiconservative replication (proven in 1960s) • Two new molecules each contain one old strand and one new strand • “Old” strand is a template for the “new” strand

  5. When DNA is replicated (copied) the entire molecule is copied • When cell divides, both new cells must contain the same DNA • In human cells, how many molecules are copied? • In what phase of the cell cycle does this take place? • In what phase of the cell cycle are the DNA molecules actually separated?

  6. How is the information in DNA used? • To make RNA (transcription) • Three kinds of RNA • Messenger RNA (mRNA)- contains the sequences from which proteins are made; unstable • Ribosomal RNA (rRNA) - part of ribosome • Transfer RNA (tRNA)- carries amino acids to site of protein synthesis • RNA is made in the nucleus, but protein synthesis occurs in the cytoplasm

  7. Both DNA and RNA are made of nucleotides

  8. When mRNA is made, only part of the DNA molecule is transcribed • What is a gene? • The gene is transcribed to make mRNA • (genotype: what is the gene?) • The gene is “expressed” when a protein is made from it • (phenotype: what type of protein is produced?) • Remember you have two copies of each gene (may or may not be identical, but one may be dominant)

  9. Transcription: RNA synthesis • One strand of DNA serves as the template • A very long piece of RNA may be produced, which is then “edited” to make a smaller RNA molecule

  10. How do you get from nucleotides to amino acids? • There are 20 different amino acids, but only four different nucleotides • Genetic code (1960s) • Three nucleotides code for one amino acid • Triplets; codons • 64 possible combinations • Some amino acids have more than one codon • Three “stop” codons

  11. What happens in translation? • Ribosome, mRNA, tRNA come together in cytoplasm • Protein synthesis usually starts with AUG codon (“start” codon) • Transfer RNA “reads” mRNA with anticodon • Transfer RNAs keep reading mRNA and adding amino acids to the growing protein • Process continues until stop codon is reached (see pp. 482-483)

  12. Mutation: a change in the DNA sequence • Substitution of one nucleotide for another • Effect depends on the actual substitution • GUUGUC both valine; no effect • GUU AUU valine isoleucine; similar amino acids so little or no effect • GUA GCA valine alanine; different chemical properties so effect may be significant • UUA UGA leucine STOP; protein is destroyed

  13. Mutation, continued • Insertion or deletion • Effect is usually serious; coding sequence is totally disrupted • THE BIG FAT DOG RAN • Insertion: THE SBI GFA TDO GRA N • Deletion: THB IGF ATD OGR AN • Imagine this effect on amino acid sequence!

  14. Certain chemicals, radiation are known to cause mutations • Mutagens • Often known to cause a specific type of mutation • May lead to disease (loss of protein function) or cancer (control gene is affected)

  15. All cells in your body (except gametes) contain the same DNA • Are all cells in your body exactly the same? • Different functions • Different stages of development • How do they look and act differently if they all have the same DNA?

  16. How is gene activity controlled? • DNA structure • Growth factors • Hormones • Regulatory genes

  17. Implications for genetic engineering • All organisms have the same DNA structure (and share many genes) • DNA sequences can be determined • Gene expression can be controlled • Mutations can be identified (and can be introduced into DNA) • DNA can be “amplified” (many copies of a DNA sequence can be produced)

  18. I. All organisms have the same DNA structure • “Recombinant DNA molecules” combine DNA from different species • Restriction enzymes cut DNA at specific sequences • Ligases join the DNA fragments together • Molecule is put into expression vector

  19. Recombinant DNA molecules, continued • Recombinant DNA molecules can be transferred to and expressed in cells • Bacteria, yeast, animal cell culture, plants, animals! • Large quantities of scarce molecules can be produced this way (growth hormone, insulin) • Genes and gene products can be studied (and modified)

  20. II. DNA sequences can be determined • Technology has been around since the 1970s • Human genome project; determine the complete DNA sequence of humans and many other organisms- why? • Similarities and differences within and between species • Evolutionary relationships • Identify genes associated with disease or other interesting variations • Learn more about gene regulation (most DNA does NOT code for genes. So what DOES it do?)

  21. III. Gene expression can be controlled • Can we turn genes “on” and “off”? • Replace damaged cells and tissues? • Some cells replace themselves easily (skin, blood) • Others do not (nerves, muscles) • Stem cells • Growth factors • Cure cancer by stopping uncontrolled cell growth? • Treat diseases that occur because of a regulatory defect? • Treat chronic infections? • Slow down the aging process?

  22. IV. Mutation analysis • DNA sequence analysis • Mutations can be deliberately introduced into DNA sequences (and then expressed) • Study effects (beneficial or harmful) • To what extent is a condition influenced by genes?

  23. Gene therapy- replacing faulty genes with functional genes • We can sequence and express genes to study protein function • We can deliver genes to the patient (vectors) • When is this appropriate? • If disease is due to a single genetic defect • If therapy is safe and effective

  24. Practical/commercial applications for recombinant DNA technology • Agriculture • Pest-resistant crops • More robust livestock • “Pharming”- transgenic organisms are used to produce pharmaceuticals • New and improved proteins • Forensic analysis

  25. (Forensic) DNA analysis • Individuals have unique DNA (except identical twins) • Criminalistics • Paternity • Human history (mitochondrial, Y chromosome) • DNA analytical techniques (PCR amplification; sequencing; probes) • Diagnostics

  26. We have known the structure of DNA only since 1953! • Technological advances have been extremely rapid • Tools for basic research • Commercial and therapeutic applications • How far can we go? • How far should we go?

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