1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 3 Cells: The Living Units: Part D

2. Copyright © 2010 Pearson Education, Inc. Cell Cycle Defines changes from formation of the cell until it reproduces Includes: Interphase Cell division (mitotic phase)

3. Copyright © 2010 Pearson Education, Inc. Interphase Period from cell formation to cell division Nuclear material called chromatin Four subphases: G 1 (gap 1)—vigorous growth and metabolism G 0 —gap phase in cells that permanently cease dividing S (synthetic)—DNA replication G 2 (gap 2)—preparation for division

4. Copyright © 2010 Pearson Education, Inc. Figure 3.31 G 1 Growth S Growth and DNA synthesis G 2 Growth and final preparations for division M G 2 checkpoint G 1 checkpoint (restriction point)

5. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Centrosomes (each has 2 centrioles) Nucleolus Interphase Plasma membrane Nuclear envelope Chromatin Interphase

6. Copyright © 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 strand

7. Copyright © 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 strand

8. Copyright © 2010 Pearson Education, Inc. DNA Replication End result: two DNA molecules formed from the original This process is called semiconservative replication

9. Copyright © 2010 Pearson Education, Inc. Figure 3.32 Adenine Thymine Cytosine Guanine Old (template) strand Two new strands (leading and lagging) synthesized in opposite directions DNA polymerase Lagging strand Leading strand Free nucleotides Old strand acts as a template for synthesis of new strand Chromosome Helicase unwinds the double helix and exposes the bases Old DNA Replication fork