Chapter 12 The Cell Cycle Lab 3 Mitosis and Meiosis

Mitosis Division of the cell nucleus. Cytokinesis Division of the cell cytoplasm.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle  The continuity of life  Is based upon the reproduction of cells, or cell division

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle – Making an “EXACT copy”  Unicellular organisms  Reproduce by cell division

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle  Multicellular organisms depend on cell division for  Development from a fertilized cell  Growth  Repair Growth and development Tissue renewal

Cell Division  Cell division results in genetically identical daughter cells  Cells duplicate their total genetic material (genome)  Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA  Cell division results in genetically identical daughter cells  Cells duplicate their total genetic material (genome)  Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Material  The DNA molecules in a cell  Are packaged into chromosomes 50 µm

Genetic Material Eukaryotic chromosomes  Consist of chromatin, a complex of DNA & protein that condenses during cell division  In animals  Somatic cells have two sets of chromosomes  46 in humans  Gametes (egg & sperm) have one set of chromosomes  23 in humans Eukaryotic chromosomes  Consist of chromatin, a complex of DNA & protein that condenses during cell division  In animals  Somatic cells have two sets of chromosomes  46 in humans  Gametes (egg & sperm) have one set of chromosomes  23 in humans

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA Replication  Each duplicated chromosome  Has two sister chromatids, which separate during cell division  They are attached by a central area called the centromere 0.5 µm Chromosome duplication (including DNA synthesis) Separation of sister chromatids chromatids centromere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phases of the Cell Cycle  The cell cycle consists of  Interphase  Mitotic phase INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitotic Phase  Mitosis consists of five distinct phases 1.) Prophase 2.) Prometaphase G 2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nonkinetochore microtubules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitotic Phase 3.) Metaphase 4.) Anaphase 5.) Telophase (usually followed by cytokinesis) Centrosome at one spindle pole Daughter chromosomes METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming

Types of Microtubules Kinetochore microtubules  Attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate Nonkinetechore microtubules from opposite poles  Overlap and push against each other, elongating the cell Kinetochore microtubules  Attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate Nonkinetechore microtubules from opposite poles  Overlap and push against each other, elongating the cell

 Assembly of the spindle microtubules starts in the centrosome.  The centrosome (microtubule-organizing center) of animals has a pair of centrioles at the center, but the function of the centrioles is somewhat undefined.  Assembly of the spindle microtubules starts in the centrosome.  The centrosome (microtubule-organizing center) of animals has a pair of centrioles at the center, but the function of the centrioles is somewhat undefined. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

 As mitosis starts, the two centrosomes are located near the nucleus.  As the spindle fibers grow from them, the centrioles are pushed apart.  By the end of prometaphase they develop as the spindle poles at opposite ends of the cell.  As mitosis starts, the two centrosomes are located near the nucleus.  As the spindle fibers grow from them, the centrioles are pushed apart.  By the end of prometaphase they develop as the spindle poles at opposite ends of the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

 Each sister chromatid has a kinetochore of proteins and chromosomal DNA at the centromere.  The kinetochores of the joined sister chromatids face in opposite directions.  During prometaphase, some spindle microtubules attach to the kinetochores.  Each sister chromatid has a kinetochore of proteins and chromosomal DNA at the centromere.  The kinetochores of the joined sister chromatids face in opposite directions.  During prometaphase, some spindle microtubules attach to the kinetochores. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

 When a chromosome’s kinetochore is “captured” by microtubules, the chromosome moves toward the pole from which those microtubules come.  When microtubules attach to the other pole, this movement stops and a tug-of-war ensues.  Eventually, the chromosome settles midway between the two poles of the cell, the metaphase plate.  Other microtubules from opposite poles interact as well, elongating the cell.  When a chromosome’s kinetochore is “captured” by microtubules, the chromosome moves toward the pole from which those microtubules come.  When microtubules attach to the other pole, this movement stops and a tug-of-war ensues.  Eventually, the chromosome settles midway between the two poles of the cell, the metaphase plate.  Other microtubules from opposite poles interact as well, elongating the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

 One hypothesis for the movement of chromosomes in anaphase is that motor proteins at the kinetochore “walk” the attached chromosome along the microtubule toward the opposite pole.  The excess microtubule sections depolymerize.  One hypothesis for the movement of chromosomes in anaphase is that motor proteins at the kinetochore “walk” the attached chromosome along the microtubule toward the opposite pole.  The excess microtubule sections depolymerize. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.7a

 Experiments support the hypothesis that spindle fibers shorten during anaphase from the end attached to the chromosome, not the centrosome. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.7b

 Nonkinetichore microtubules are responsible for lengthening the cell along the axis defined by the poles.  These microtubules interdigitate across the metaphase plate.  During anaphase motor proteins push microtubules from opposite sides away from each other.  At the same time, the addition of new tubulin monomers extends their length.  Nonkinetichore microtubules are responsible for lengthening the cell along the axis defined by the poles.  These microtubules interdigitate across the metaphase plate.  During anaphase motor proteins push microtubules from opposite sides away from each other.  At the same time, the addition of new tubulin monomers extends their length. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinesis In animal cells  Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinesis  In plant cells, during cytokinesis  A cell plate forms Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Control system G 2 checkpoint M checkpoint G 1 checkpoint G1G1 S G2G2 M

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell Cycle Control System  The clock has specific checkpoints  Where the cell cycle stops until a go-ahead signal is received G 1 checkpoint G1G1 G1G1 G0G0 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Normal Cell Behavior In density-dependent inhibition  Crowded cells stop dividing Most animal cells exhibit anchorage dependence  In which they must be attached to a substratum to divide Cells anchor to dish surface and divide (anchorage dependence) When cells have formed a complete single layer, they stop dividing (density-dependent inhibition) If some cells are scraped away, the remaining cells divide to fill the gap and then stop 25 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Abnormal Cell Behavior Cancer cells  Transformation is the process of a normal cell becoming cancerous  Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence  Why cells transform is often a mystery but most likely genes controlling the cell control system are involved 25 µm Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cancerous Cells  Malignant tumors invade surrounding tissues and can metastasize  Exporting cancer cells to other parts of the body where they may form secondary tumors Cancer cells invade neighboring tissue. 2 A small percentage of cancer cells may survive and establish a new tumor in another part of the body. 4 Cancer cells spread through lymph and blood vessels to other parts of the body. 3 A tumor grows from a single cancer cell. 1 Tumor Glandular tissue Cancer cell Blood vessel Lymph vessel Metastatic Tumor

Thinking Question Many cancer drugs (chemotherapy) work by interfering with the production or proper function of microtubules. What specific effect would this have on cell division and why is this beneficial in the treatment of cancer? Common side effects of chemotherapy are hair loss and nausea. Why do you think this is the case?

Key Points of Chapter 12  Cell division results in two genetically identical daughter cells  The mitotic phase alternates with interphase in the cell cycle  The cell cycle is regulated by a molecular control system  Cell division results in two genetically identical daughter cells  The mitotic phase alternates with interphase in the cell cycle  The cell cycle is regulated by a molecular control system