Part I-B: DNA Replication and Cell Cycle PDF

PART I-B 1. DNA content of cells 2. Cell cycle (eukaryotes) 3. DNA replication (E. coli) 4. Differences DNA replication (prokaryotes vs eukaryotes) 5. Meiosis (eukaryotes) 1. DNA CONTENT OF CELLS  number of n-value...

PART I-B 1. DNA content of cells 2. Cell cycle (eukaryotes) 3. DNA replication (E. coli) 4. Differences DNA replication (prokaryotes vs eukaryotes) 5. Meiosis (eukaryotes) 1. DNA CONTENT OF CELLS  number of n-value chromosomes in 1 set DNA content weight of 1 set C-value of chromosomes (pg) For animals, gametes are considered a ‘reference’ set as they have n chromosomes and a DNA content of C.  Chromosomes sets or Humans 2n=46 Homologous pair: C value: Similar DNA sequence 6.41 pg for males Same genes at same loci 6.51 pg for females Location of centromere 2. DNA REPLICATION Mitosis (cell cycle) Meiosis NOTE: HOMOLOGS DO NOT PAIR DURING MITOSIS!! Homologs separate Equational division Terminal cell differentiation Organ has reached size Organelle and Cell starvation protein synthesis. Origin licensing. S G1/ oint ck p Che 2 /M oint G kp h ec C DNA is checked for integrity Repairs are made 3. DNA REPLICATION IN MODEL ORGANISM E. coli Bacteria use DNA replication to prepare for binary fission. Eukaryotes use DNA replication for both mitosis and meiosis.  10 Structure of the OriC (E. coli) Note: this image has been updated  Initiation (DNA replication) Note: this image has been updated  Elongation (DNA replication) RNA primers (red) = 10-60 nt Note: this image has been updated G C T A Remember DNA is antiparallel G C  15 Elongation (DNA replication) (DnaB) (DnaG)  Termination (DNA replication) Permissive Counter- Clockwise side clockwise advancing advancing fork fork terH terJ Non-permissive terI side terminus of chromosome terG replication at a site (dif) terE terF terA terD terB terC 10 ter sites + TUS proteins  19 Termination TUS protein binds terminator sequence ter (10 x 23-mers, A-J) DNA replication stops when the replisome encounters the Tus-Ter complex Decatenase Topoisomerase IV separates the two resulting circular chromosomes (DNA catenanes)  Good DNA Replication Video https://youtu.be/jmWuju1S9_E?si=1Bo5Bgtd41I7uxbi 3. DNA REPLICATION IN EUKARYOTES  One replicated chromosome showing two sister One unreplicated One replicated chromosome chromatids chromosome showing two sister chromatids (metaphase) (interphase) (interphase) Metaphase I G1 S G2 or Metaphase In eukaryotes, sister chromatids are held together by cohesins  24 Differences in DNA replication between prokaryotes and eukaryotes are due to: Eukaryotic genomes are larger than bacterial genomes: Ex: the human genome is 1200X larger than E. coli’s. Ekaryotes have a slower replication machinery than prokaryotes: Ex: Eukaryotic replisomes are ~40X slower than those of prokaryotes Eukaryotes have linear chromosomes whereas bacteria have circular chromosomes. When compared to prokaryotes, eukaryotic genomes and cells have greater structural complexity.  25 Differences between prokaryotic and eukaryotic genomes DNA replication Prokaryote DNA rep Eukaryote DNA rep Cytoplasm Nucleus Location and timing Any time S phase Origin(s) of replication One (OriC) 5 x 104 origins of replication, which require licensing during late G1 Complexes are larger and include Replisome and Less more proteins replication proteins Ex: one replication polymerase Ex: three replication polymerases Chromatin (DNA + histones + other proteins). DNA DNA + NAPs Eukaryotic replisome works with chromatin remodeling complexes. Okazaki fragments Larger (1,000-2,000 bp) Smaller (100-200 bp) Termination of No formal termination sequence replication ter site 3’ overhang at telomeres One vs multiple origins of replication Circular dsDNA chromosome Linear, dsDNA chromosome Electron micrograph shows nucleosomes before and after replication fork (arrow) Telomeres Any issues with this graph?  29 Example problem: Look at these replicating DNA molecules. In which direction would continuous DNA synthesis take place? How about discontinuous synthesis? Where would the primers be placed by primase? Identify all 3’ and 5’ ends. THANK YOU ADDITIONAL SLIDES  Elongation (DNA replication) Lagging strand (DNA synthesis is Leading strand discontinuous) DNA Pol III (DNA synthesis is continuous) Primosome (DnaB, DnaG) Sliding clamp Leading strand (DNA synthesis is Lagging strand continuous) (DNA synthesis is discontinuous) Primers (RNA, in red) Function of gyrase https://youtu.be/T06lo8T8Pmw?si=_hSm0eaLIxOjFnNu Cell cycle (eukaryotes) Mitosis DNA replication Initiation (DNA replication) 3 x 13-mers 12? x 9-mers 39 BOTH Mitosis and Meiosis begin with DNA replication!