Lecture 3 cell cycle and dna replication-dr faisal al-allaf


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Lecture 3 cell cycle and dna replication-dr faisal al-allaf

  1. 1. Dr. Faisal Al-Allaf Assistant Professor of Genetics and Molecular Medicine Umm Al-Qura University Faculty of Medicine, Makkah, Saudi Arabia fallaf@uqu.edu.sa Tel/Fax: 5270000 Ext: 4198 The Cellular and Molecular Basis of Inheritance1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 1
  2. 2. ‫ﻟﺘﺴﻬﻴﻞ ﻓﻬﻢ اﻟﻤﺤﺘﻮى اﻟﻌﻠﻤﻲ واﻟﺤﺼﻮل ﻋﻠﻰ آﺎﻣﻞ اﻟﺪروس ﻟﻬﺬا اﻟﻤﻘﺮر‬‫ﻓﺴﻴﺘﻢ ﺗﻔﻌﻴﻞ اﻟﺘﻌﻠﻴﻢ اﻹﻟﻜﺘﺮوﻧﻲ ﻋﻦ ﺑﻌﺪ. ﺳﻴﺘﻴﺢ ﻟﻚ اﻟﺘﻌﻠﻴﻢ اﻹﻟﻜﺘﺮوﻧﻲ ﻓﺮﺻﺔ‬‫إﺟﺮاء اﻹﻣﺘﺤﺎﻧﺎت واﻟﻤﺬاآﺮة واﻹﺳﺘﺮﺟﺎع ﻣﻦ اﻟﺒﻴﺖ. آﻤﺎ ﺳﻴﻤﻜﻨﻚ ﻣﻦ‬‫اﻟﺤﺼﻮل ﻋﻠﻰ اﻟﻨﺴﺦ اﻻﻟﻴﻜﺘﺮوﻧﻴﺔ ﻟﻠﺪروس. ﺑﺈﻣﻜﺎﻧﻨﺎ أﻳﻀﺎ إﺟﺮاء اﻟﺤﻮارات‬ ‫ﺣﻮل ﻣﻮاﺿﻴﻊ اﻟﻤﻘﺮر وﺑﺈﻃﻼع اﻟﺠﻤﻴﻊ.‬ ‫ﻟﺘﻔﻌﻴﻞ ﺗﺴﺠﻴﻠﻚ ﻓﻲ اﻟﺘﻌﻠﻴﻢ اﻹﻟﻴﻜﺘﺮوﻧﻲ ﻋﻦ ﺑﻌﺪ ، ﻧﺮﺟﻮ زﻳﺎرة اﻟﺮاﺑﻂ:‬‫‪http://el.uqu.edu.sa/jusur/index.php?un_id=uqu‬‬ ‫ﻟﻺﻃﻼع ﻋﻠﻰ اﻟﻤﻌﻠﻮﻣﺎت اﻟﺨﺎﺻﺔ ﺑﺄﺳﺘﺎذ هﺬا اﻟﻤﻘﺮر وﻣﻌﺮﻓﺔ اﻟﺴﺎﻋﺎت‬ ‫اﻟﻤﻜﺘﺒﻴﺔ ﻟﻠﺘﻮاﺻﻞ ﻣﻌﻪ ، ﻧﺮﺟﻮ زﻳﺎرة اﻟﺮاﺑﻂ:‬‫‪http://www.uqu.edu.sa/faallaf‬‬ ‫40/40/1341‬ ‫‪Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa‬‬ ‫2‬
  3. 3. Course contents (syllabus)GENOME, TRANSCRIPTOME, AND PROTEOME Cell, DNA and RNA Gene structure and genetic codes Cell cycle and DNA replication Transcription and post-transcriptional modification RNA and regulation of gene expression Translation and post-translational modificationCHROMOSOMES AND CELL DIVISION Chromosomes morphology and classification Cell cycle division Mitosis Meiosis1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 3
  4. 4. How genetic information is transmittedfrom one generation to the next? The body grow by increasing in cell size and cell number (mitosis). Body growth involves individual cells replicating their components, dividing in half, expanding and doing the same again. This sequence is called the cell cycle and it involves two critical events: Replication of chromosomal DNA Segregation of the duplicated chromosomes by mitosis1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 4
  5. 5. The cell cycle Cell proliferate in response to extracellular factors (growth factors, hormones, and cell-cell interactions). The cell cycle is driven by activation and deactivation of enzymes known as cyclin-dependent protein kinasesCell cycle has four major phases:1. Interphase (G1, S, G2)2. Mitosis (M) phase 1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 5
  6. 6. G1 phase is the Gap betweenM- and S-phases During G0 the cell decides to divide, die, or stay differentiated G1-phase The cytoplasm increases in volume (proteins, carbohydrates and lipid synthesized) Damage to the DNA is repaired. If the nuclear DNA is damaged, a protein called p53 increases in activity and stimulate p21 to arrest the cells at G1 phase. If the repair failed the cell committed suicide (apoptosis) The cell checks that its environment is favourable before committing itself to S-phase1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 6
  7. 7. S-phase is the DNA synthesisphase in which DNA copy itself S-phase DNA synthetic enzymes activated, DNA replicated, and centriols begin to duplicate From the end of S-phase to the middle of M phase there are 23 pairs of chromosomes, each contain two sister chromatides (2C) At the middle of M, there are 23 pairs of chromosomes but 92 nuclear DNA double-helices (4C) G1 and G0 are the only phases of the cell cycle throughout which 46 chromosomes correspond to 2C DNA molecules S-phase lasts about 8 hours1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 7
  8. 8. G2-phase is the gap between S-phase and mitosis G2-phase Completion of DNA synthesis checked Cell volume checked M-phase cyclin dependent kinases activated Centrioles duplication complete The second checkpoint on cell size occurs during G21431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 8
  9. 9. Three checkpoints in the cell cycle G1/S checkpoint: at the end of G1 the cell becomes committed to completing a cycle of division. The cell will not proceed beyond this point if there are inadequate nutrients or growth factors G2/M checkpoint: cells will not proceed beyond this point if there is DNA damage(s) M/G2 checkpoint: cells will become arrested at this stage if the mitotic spindle fails to assemble adequately1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 9
  10. 10. DNA replication is initiated atorigins of replication Heterochromatin replicates later in S- phase than euchromatin Replication is initiated at multiple points known as Replication origins The DNA double helix is split open by a DNA helicase to expose the base sequences The resulting separations of the DNA strand are called Replication bubbles Two replication complexes form at each origin, one at each end of the bubble and is a Y-shaped structure called Replication fork1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 10
  11. 11. Replication is mediated by enzymescalled DNA polymerases DNA polymerases synthesized new DNA from deoxyribonucleotide triphosphates (ATP, GTP, CTP, and TTP) which are converted into mononphosphate nucleotides (AMP, GMP, CMP and TMP) The release and hydrolysis of phosphate from the triphosphates provide energy for the reaction and it ensures that it is irreversible Unlike RNA polymerase, DNA polymerase has an absolute requirement for a perfectly base-paired nucleotide which has important consequences: DNA polymerase requires a primer on which to initiate extension It will pause if an incorrect base is inserted The primers are synthesized by RNA polymerase Primers, energy, templates, enzymes (polymerases, helicase, ligase, topoisomerase, primase, telomearse)1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 11
  12. 12. DNA synthesis of both strands occurs in the 5` to 3` direction DNA can copy itself and each strand directing the synthesis of a complementary one The synthesis of both new complementary strands occurs in the 5` to 3` direction; meaning that replication moving along the template strands from 3’ to 5’ There are three stages for DNA replication: 1. Initiation 2. Elongation 3. Termination1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 12
  13. 13. Initiation of DNA replication1. Helicase binds to origin of replication and unwind (separates) parental strands2. Single-strand binding proteins (SSBs) keep strands apart3. Primase binds to the helicase to form the primosome which synthesizes the RNA primer (a short stretch of RNA on the DNA template)1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 13
  14. 14. Elongation of DNA1. DNA polymerase clamps to the leading strand and adds DNA nucleotides to the RNA primer2. DNA polymerase proofreading activity checks and replaces incorrect bases3. Continuous (leading) strand synthesis produces new fragments on the 3’ to 5’ template but in a 5’ to 3’ direction4. Discontinuous (lagging) strand synthesis produces Okazaki fragments on the 5’ to 3’ template but in a 5’ to 3’ direction5. Replication proceeds along the single strands at about 40-50 nucleotides per second, simultaneously in both directions 1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 14
  15. 15. DNA replication fork The new sections of DNA along the lagging strand are typically 100-200 bases long and are known as Okazaki fragments Leading strand synthesized in a continuous process from a single RNA primer by DNA polymerase δ and lagging strand synthesized in pieces called Okazaki fragment from multiple RNA primers by DNA polymerase α The strand that is leading and the strand that is lagging depends on the direction the replication complexes is migrating Following synthesis of lagging strands, they are linked together by action of the enzyme DNA ligase Note that mitochonderial DNA replication occurs independently of that in the nucleus and utilizes a different set of enzymes1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 15
  16. 16. Replication fork1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 16
  17. 17. Termination of DNA replication Enzymes remove RNA primers DNA ligase joins up adjacent Okazaki fragments and seals other nicks in the sugar- phosphate backbone1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 17
  18. 18. DNA replication is semi-conservative The process of DNA replication is termed semi-conservative, as only one strand of each serves as a template for synthesis of a new strand Therefore, only one strand is conserved in each double- stranded DNA molecule After the replication fork passes, chromatin structure is reformed by the addition of new histones1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 18
  19. 19. Post-replication repair enzymes andbase mismatch proofreading systems Using the template strand as a guide, the following enzymes are responsible for repair mechanism: Endonuclease detects mismatch or error Exonuclease removes nucleotides from nick to past defect Polymerase (β and ε) replace the erroneously inserted bases DNA Ligase rejoin the double strands1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 19
  20. 20. 1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 20
  21. 21. References and Private Reading These slides are only a handout and the students must read the text book (Emery’s element of medical genetics)1. Emery’s Elements of Medical Genetics, 13th edition 2007, by Peter TURNPENNY and Sian ELLARD. Churchill Livingstone ELSEVIER. ISBN: 978-0-7020-2917-22. Medical Genetics at a Glance, 2nd edition 2008, by Dorian PRITCHARD and Bruce KORF. Blackwell Publishing. ISBN: 978-1-4051-4846-73. Genetics for Dummies, 2005, by Tara Robinson, Wiley Publishing, Inc. ISBN: 978- 0-7645-9554-74. Cell Biology and Genetics, Crash Course, 2nd edition 2006, by Manson, Jones, Morris, Michael STEEL and Dan HORTON-SZAR. MOSBY ELSEVIER. ISBN: 0- 7234-3248-15. Human Molecular Genetics, 3rd edition, 2003, by STRACHAN T. and A. READ. Garland science/Taylor and Francis group. ISBN: 978-0-8153-4182-66. Genomes, 3rd edition 2006, by T.A. BROWN. Garland science, ISBN: 978-0-8153- 4138-31431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 21
  22. 22. Acknowledgments For the providers of all the educational materials (video clips, pictures, diagrams and charts) including publishers, pharmaceutical companies or unknown internet users who made their material available for use, in this and other presentations, I offer heartfelt thanks and deep appreciation. I feel particularly grateful to faculty, staff, and our brilliant students who provided a unique intellectual and wonderful environment for work.1431/04/04 Dr. Faisal Al-Allaf, fallaf@uqu.edu.sa 22