Chapter 12 The Cell Cycle-Updated.ppt

Chapter 12 The Cell Cycle PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: The...

Chapter 12 The Cell Cycle PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: The Key Roles of Cell Division • The ability of organisms to reproduce best distinguishes living things from nonliving matter. • The continuity of life is based on the reproduction of cells, or cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Multicellular organisms depend on cell division for: – Development from a fertilized cell – Growth – Repair Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 12.1: Cell division results in genetically identical daughter cells • Cell division results in daughter cells with identical genetic information, DNA. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cellular Organization of the Genetic Material • All the DNA in a cell constitutes the cell’s genome. • A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells). • DNA molecules in a cell are packaged into chromosomes. • Gene: is the fundamental units of heredity responsible for a given trait. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus • Somatic cells (non-reproductive cells) have two sets of chromosomes • Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells. • Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Distribution of Chromosomes During Eukaryotic Cell Division • In preparation for cell division, DNA is replicated and the chromosomes condense • Each duplicated chromosome has two sister chromatids, which separate during cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Distribution of Chromosomes During Eukaryotic Cell Division • A chromatid is a one copy of a newly copied chromosome which is joined to the original copy by a single centromere. • The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached. Fig. 12-4 0.5 µm Chromosomes Chromosome arm Centromere DNA molecules Chromosome duplication (including DNA synthesis) Sister chromatids Separation of sister chromatids Centromere Sister chromatids Phases of the Cell Cycle • The cell cycle consists of – Mitotic (M) phase (mitosis and cytokinesis) – Interphase (cell growth and copying of chromosomes in preparation for cell division) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Eukaryotic cell division consists of: – Mitosis, the division of the nucleus – Cytokinesis, the division of the cytoplasm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Interphase (about 90% of the cell cycle) can be divided into sub-phases: – G1 phase (“first gap”) Cell Grows and Functions Normally – S phase (“synthesis”) Chromosomes are Duplicated – G2 phase (“second gap”) Cel Grows and Prepares for Divison • Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Interphase • The cell grows during all three phases of Interphase, but chromosomes are duplicated only during the S phase. Fig. 12-5 S (DNA synthesis) G1 Mi to si s in k to y C is s e MIT (M) OTIC PHA SE G2 • Mitosis is conventionally divided into five phases: – Prophase – Prometaphase – Metaphase – Anaphase – Telophase • Cytokinesis is well underway by late telophase BioFlix: Mitosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 1) Prophase: A stage of Mitosis at which the chromatin condenses into two rod-shaped structures called sister chromatids. • 2) During prometaphase, some spindle microtubules attach to the kinetochores of centromere and begin to move the sister chromatids • 3) At metaphase, the sister chromatids are all lined up at the metaphase plate, the midway point between the spindle’s two poles • 4) In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell • 5) In telophase, genetically identical daughter nuclei form at opposite ends of the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Centrosome • A small region of cytoplasm adjacent to the nucleus that contains the centrioles and serves to organize microtubules. • Centrosomes are responsible for the initiation of cytokinesis (the splitting up of the mother cell into two). • Each centrosome consists of two centrioles. Chromosomes During Mitosis Fig. 12-6b Prophase G2 of Interphase Chromatin Centrosomes (with centriole (duplicated) pairs) Early mitotic Aster spindle Nucleolus Nuclear Plasma envelope membrane Prometaphase Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Kinetochore Nonkinetochore microtubules Kinetochore microtubule Fig. 12-7 Aster Centrosome Sister chromatids Microtubules Chromosomes Metaphase plate Kinetochores Centrosome 1 µm Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm Fig. 12-6d Metaphase Anaphase Metaphase plate Spindle Centrosome at one spindle pole Telophase and Cytokinesis Cleavage furrow Daughter chromosomes Nuclear envelope forming Nucleolus forming Cytokinesis: A Closer Look • In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow • In plant cells, a cell plate forms during cytokinesis Animation: Cytokinesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-9a 100 µm Cleavage furrow Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) Fig. 12-9b Vesicles forming cell plate Wall of parent cell Cell plate 1 µm New cell wall Daughter cells (b) Cell plate formation in a plant cell (TEM) Binary Fission • Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission • In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-11-4 Origin of replication E. coli cell Two copies of origin Origin Cell wall Plasma membrane Bacterial chromosome Origin The Cell Cycle Control System • The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock. • The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-14 G1 checkpoint Control system G1 M G2 M checkpoint G2 checkpoint S • For many cells, the G1 checkpoint seems to be the most important one. • If a cell receives a go-ahead signal at the G 1 checkpoint, it will usually complete the S, G 2, and M phases and divide. • If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 12-15 G0 G1 checkpoint G1 (a) Cell receives a go-ahead signal G1 (b) Cell does not receive a go-ahead signal