Download Ch.10 - Jamestown School District

Unit 4 Genetics
Ch. 10 Cell Growth & Division
Cell Growth
 In most cases, living things grow by
producing more cells
 The cells of an adult animal are no
larger than the cells of a young animal,
there are just more of them
Limits to Cell Growth
 There are 2 reasons why cells divide
instead of continuing to grow
indefinitely
 The larger a cell becomes, the more
demands it places on its DNA
 Also, the cell has more trouble moving
enough nutrients & wastes across the
cell membrane
Divisions of the Cell
 Cell division - the process where a cell
divides into 2 new daughter cells
 Before cell division occurs, the cell
replicates (copies), all of its DNA
 Each daughter cell gets a complete
copy of that genetic information
Cell Division
 Mitosis - the 1st stage, division of the
nucleus
 Cytokinesis - the 2nd stage, division of
the cytoplasm
Cell Division
 Reproduction by mitosis is classified as
asexual, since the cells produced by
mitosis are genetically identical to the
parent cell
 It is also a source of new cells when a
multicellular organism grows &
develops
Chromosomes
 In eukaryotic cells, the genetic info
passed from 1 generation of cells to
the next is carried by chromosomes
 Chromosomes are made up of DNA
(which carries the cell’s coded genetic
info) & proteins
Chromosomes
 The cells of every organism have a
specific # of chromosomes
 Every human cell (except sex cells),
have 23 pairs of chromosomes or 46
individual chromosomes
Chromosomes
 Before cell division, each chromosome
is copied
 Each chromosome consists of 2
identical “sister” chromatids
 When a cell divides, 1
chromatid goes to each of the
2 new cells
Chromosomes
 Each pair of chromatids is attached at
the center - centromere
The Cell Cycle
 Interphase - the “in-between” period
of growth
 Cell cycle - the series of events that
cells go through as they grow
The Cell Cycle
 During the cell cycle, a cell grows,
prepares for division, & divides to form
2 daughter cells, each of which then
begins the cycle again
 The cycle consists of 4 phases
The Cell Cycle
 Mitosis & cytokinesis takes place during
the M phase
 Chromosome replication, or synthesis
(to make), takes place during the S
phase
 When the cell copies the
chromosomes, it makes a duplicate set
of DNA
The Cell Cycle
 Between the M and S phase are G1 and
G2
 The G phases are periods of intense
growth
Mitosis
 Biologists divide the events of mitosis
into 4 phases: prophase, metaphase,
anaphase, & telophase
 Prophase:
 The 1st & longest phase of mitosis, when
the chromosomes become visible
 Centrioles - 2 tiny structures in the
cytoplasm, separate & move to opposite
sides of the nucleus
Mitosis
 Prophase:
 The centrioles help to organize the
spindle- a fanlike structure that helps
separate the chromosomes
 The nucleolus disappears, & the nuclear
envelope breaks down
Mitosis
 Metaphase:
 The 2nd phase of mitosis that only lasts a
few minutes
 The chromosomes line up in the middle
Mitosis
 Anaphase:
 The 3rd phase of mitosis, when the
centromeres split, allowing the sister
chromatids to separate & become
individual chromosomes
 The chromosomes continue to move until
they have separated
into 2 groups at the
poles
Mitosis
 Telophase:
 The 4th & final phase of mitosis, a nuclear
envelope begins to form around each
cluster of chromosomes at the poles
 The spindle begins to break apart, & a
nucleolus becomes visible in each
daughter cell
QuickTime™ and a
 Mitosis is complete
TIFF (Uncompressed) decompressor
are needed to see this picture.
Mitosis
 Remember: IPMAT, (Interphase,
Prophase, Metaphase, Anaphase, &
Telophase)
Cytokinesis
 As a result of mitosis, 2 nuclei (each
with the same set of chromosomes) are
formed, within the cytoplasm of a
single cell
 All that is left to complete the M phase
of the cell cycle, is to divide the
cytoplasm itself
Cytokinesis
 Cytokinesis usually occurs at the same
time as telophase
Cell Cycle Regulators
 Cyclin - protein that regulates the cell
cycle
 Cyclins regulate the timing of the cell
cycle in eukaryotic cells
Uncontrolled Cell Growth
 Cancer - disorder where some of the
body’s own cells lose the ability to
control growth
 Cancer cells do not respond to the
signals that regulate the growth of
most cells