3Cell CycleInterphaseSlide 4Slide 5DNA ReplicationSlide 7Slide 8Slide 9PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal CollegeC H A P T E RCopyright © 2010 Pearson Education, Inc.3 Cells: The Living Units: Part DCopyright © 2010 Pearson Education, Inc.Cell Cycle•Defines changes from formation of the cell until it reproduces•Includes:•Interphase•Cell division (mitotic phase)Copyright © 2010 Pearson Education, Inc.Interphase•Period from cell formation to cell division•Nuclear material called chromatin•Four subphases:•G1 (gap 1)—vigorous growth and metabolism•G0—gap phase in cells that permanently cease dividing•S (synthetic)—DNA replication•G2 (gap 2)—preparation for divisionCopyright © 2010 Pearson Education, Inc.Figure 3.31G1GrowthSGrowth and DNAsynthesisG2Growth and finalpreparations fordivisionMG2 checkpointG1 checkpoint(restriction point)Copyright © 2010 Pearson Education, Inc.Figure 3.33Centrosomes(each has 2centrioles)NucleolusInterphasePlasmamembraneNuclearenvelopeChromatinInterphaseCopyright © 2010 Pearson Education, Inc.DNA Replication•DNA helices begin unwinding from the nucleosomes•Helicase untwists the double helix and exposes complementary chains•The Y-shaped site of replication is the replication fork•Each nucleotide strand serves as a template for building a new complementary strandCopyright © 2010 Pearson Education, Inc.DNA Replication•DNA polymerase only works in one direction•Continuous leading strand is synthesized•Discontinuous lagging strand is synthesized in segments•DNA ligase splices together short segments of discontinuous strandCopyright © 2010 Pearson Education, Inc.DNA Replication•End result: two DNA molecules formed from the original•This process is called semiconservative replicationCopyright © 2010 Pearson Education, Inc.Figure 3.32AdenineThymineCytosineGuanineOld (template) strandTwo new strands (leading and lagging)synthesized in opposite directionsDNA polymeraseDNA polymeraseLaggingstrandLeading strandFree nucleotidesOld strand acts as atemplate for synthesisof new strandChromosomeHelicase unwindsthe double helix andexposes the basesOld
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