Post on 17-Feb-2017
THE CELLCYCLE
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
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(a) Reproduction (b) Growth and development
(c) Tissue renewal
Phases of the Cell Cycle The cell cycle consists ofInterphase (cell growth
and copying of chromosomes in preparation for cell division)Mitotic (M) phase (mitosis and cytokinesis)
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Interphase (about 90% of the cell cycle) can be divided into sub-phases:G1 phase (“first gap”)S phase (“synthesis”)G2 phase (“second gap”)
The cell grows during all three phases, but chromosomes are duplicated only during the S phase
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 12-5
S(DNA synthesis)
MITOTIC(M) PHASEMito
sis
Cytokin
esis
G1
G2
Mitosis is conventionally divided into four phases:ProphaseMetaphaseAnaphaseTelophase
Cytokinesis is well underway by late telophase
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Structure of Chromosomes The centromere is a
constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.
Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division:
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Metaphase chromosome
Kinetochore
Kinetochoremicrotubules
Centromereregion ofchromosome
Sister Chromatids
Mitosis and
Meiosis
Mitosis and Meiosis Mitosis:-division of somatic (body) cells
Meiosis-division of gametes (sex cells)
Interphase1.Cell preparing to divide2.Genetic material doubles
Prophase1. Chromosomes thicken and shorten
-become visible-2 chromatids joined by a centromere
2. Centrioles move to the opposite sides of the nucleus
3. Nucleolus disappears4. Nuclear membrane disintegrate
Metaphase Chromosomes meet in the middle!1. Chromosomes arrange at equator of
cell2. Become attached to spindle fibres
by centromeres3. Homologous chromosomes do not
associate
Anaphase Chromosomes get pulled
apart1. Spindle fibres contract
pulling chromatids to the opposite poles of the cell
Telophase Now there are two!1. Chromosomes uncoil2. Spindle fibres disintegrate3. Centrioles replicate4. Nuclear membrane forms5. Cell divides
Meiosis 4 daughter cells produced Each daughter cell has half the chromosomes of the parent
2 sets of cell division involved