Cell Growth 2 things limit the size of cells as they grow:
Access to DNAif cell is too big, too hard to get to DNA for
instructions Access to materialsif cell is too big, cell membrane
is not big enough to move things in and out (surface area changes
by factor of 2, volume by factor of 3) So when cells grow too big,
they divide
Slide 3
Asexual Reproduction Sometimes cells divide and make exact
copies of themselves No change in DNA/genetic info. Cells are
genetically identical e.g. bacteria, many single celled organisms,
plants (can)
Slide 4
Sexual Reproduction Sometimes organisms make gametes and
exchange genetic information gametes (egg and sperm, egg and
pollen) new cells are genetically different from originals new
cells have only the genetic info of original
Slide 5
DNA/chromosomes DNA : DeoxyriboNucleic Acid Chemical that holds
information on cell functions Has different shapes/forms during
life of cell Chromatin: long thin strands of DNA, spends most of
its time in this form Chromosome: Rod- shaped structures, DNA and
protein (histones), only in this form during cell division
Chromatid: two halves of a chromosome Centromere: the point where
two chromatids are joined
Slide 6
DNA/chromosomes
Slide 7
Different kinds/shapes of chromosomes sex chromosomes: X and Y
chromosomes, XX is female, XY is male. autosomes: Other chromosomes
besides the sex chromosomes homologous chromosomes Same shape/genes
1 from Mom and 1 from Dad If a cell has the normal number of
chromosomes, it is called diploid. That means it will have 2 of
each chromosome. Body cells are diploid, 2n = 46 for humans 22
pairs autosomes, 1 pair sex chromosomes Some cells are haploid,
have the number of chromosomes Gametes are diploid n = 23 for
humans
Slide 8
Cell cycle Events of a cells life 4 stages G 1 : growth: Cells
grow to mature size S: synthesis: DNA is copied G 2 : growth: Cell
prepares for division M: mitosis: cell divides
http://www.cellsalive.com/cell_cyc le.htm (ISH)
http://www.cellsalive.com/cell_cyc le.htm Interphase: G1, S and G2
together are known as interphase between phases and not part of
mitosis. Also a G 0 phase. Cells do not copy DNA or prepare for
mitosis, but are still alive (e.g. nervous system)
Slide 9
Regulating the cell cycle After each phase (G 1, S, G 2 ) of
the cell cycle, the cell checks itself to make sure no mistakes
have been made. These are called checkpoints. Sometimes something
goes wrong (a mutation ) and the cell does not check itself and the
cell cycle just keeps growing and dividing rapidly We call that
cancer. Mutant cells divide out of control and form a tumor.
Slide 10
Mitosis (prophase, metaphase) What happens during prophase:
Centrioles, spindles appear Chromosomes become visible (Chromatin
tightens and coils) Nuclear membrane breaks down and disappears
What happens during metaphase: Chromosomes move to middle/equator
of cell Randomly assorted (doesnt matter what order)
Slide 11
Mitosis (anaphase, telophase) What happens during anaphase:
Chromosomes split at centromere and daughter chromatids move to
ends of cell What happens during telophase: Cell starts to pinch in
Nucleus starts to reform Chromosomes are at opposite ends, unwind
back into chromatin
Slide 12
Mitosis (Cytokinesis) Mitosis technically refers to just
division of the nucleus Division of the rest of the cell is called
cytokinesis Cytoplasm and contents (other organelles) divide
Cleavage furrow forms in animals where cell membrane pinches in in
plants, cell membrane cant pinch in so new cell wall forms in
middle, called cell plate. http://www.millerandlevine.com/chapter/1
0/ (vid) http://www.millerandlevine.com/chapter/1 0/
http://www.cellsalive.com/mitosis.htm (ISH)
http://www.cellsalive.com/mitosis.htm Pick the cell stage:
http://www.classzone.com/books/ml_sci_li
fe/page_build.cfm?id=resour_ch3&u=1##
http://www.classzone.com/books/ml_sci_li
fe/page_build.cfm?id=resour_ch3&u=1##
Slide 13
Slide 14
Meiosis (prophase I) Go through 2 cell divisions, 4 daughter
cells start with diploid number of chromosomes and end up with
haploid number of chromosomes Prophase I similar to mitosis:
Nuclear membrane breaks down Chromatin forms chromosomes Centrioles
move to ends Whats different: Line up by shape (homologous),
process is called synapsis. Forms a tetrad. Crossing over can
occur: part of 1 chromosome changes with same part of its
homolog.
Slide 15
Meiosis (anaphase I,metaphase I) Metaphase I Whats similar to
mitosis: Chromosomes line up in the middle Independent assortment:
which homolog is on which side is random Whats different: Line up
according to shape (tetrads line up, rather than individual
chromosomes) Anaphase I Whats similar to mitosis: Chromosomes
(tetrads) split apart and move to end of cell Whats different:
homologs split apart centromeres dont split * cells will now be
haploid*
Slide 16
Meiosis (telophase I) Telophase I Whats similar to mitosis: 2
cells are formed chromosomes are at the ends of the cell nucleus
reforms cytokinesis happens next Whats different: haploid cells
with 2 copies of the same chromosome, not 1 copy of different
chromosomes Meiosis I is called reduction division, because youve
reduced the cell from diploid to haploid
Slide 17
Meiosis II (prophase II & metaphase II) The two daughter
cells then undergo a second division with the same stages/events.
Prophase II Whats similar to mitosis: Spindles form Chromosomes
move towards center Nucleus breaks down Whats different: Nothing.
Its exactly the same, except that the cell is haploid. Metaphase II
Whats similar to mitosis: Chromosomes line up in the middle Whats
different: Nothing. Its exactly the same, except that the cell is
haploid.
Slide 18
Meiosis II (anaphase II & telophase II) Anaphase II Whats
similar to mitosis: Individual chromatids are moved towards
opposite ends of the cells centromere splits Whats different:
Nothing. Its exactly the same, except that the cell is haploid.
Telophase II Whats similar to mitosis: Nucleus reforms around the
chromatids Cytokinesis (cell membrane pinches in, organelles divide
and cells separate) Whats different: 4 cells are formed (total)
Nothing. Its exactly the same, except that the cell is haploid.
http://www.cellsalive.com/meio sis.htm
http://www.cellsalive.com/meio sis.htm
Slide 19
Genetic Variations Two things that can happen during meiosis
that can recombine DNA for future generations: Crossing over:
During prophase I: In the tetrad, pieces of chromatids break off
and switch places. Genes exchanged between Moms and Dads
chromosomes Independent assortment: Homologous chromosomes randomly
are separated in Metaphase I. Genes passed on are randomly picked.
These will be important ideas when we get to talking about genetics
in a couple of units.
Slide 20
Comparing Mitosis and Meiosis Each starts with a diploid cell.
Mitosis ends up with 2 diploid cells exactly identical Meiosis ends
up with 4 haploid cells not identical
Slide 21
Cell division in Prokaryotes (bacteria) Prokaryotic cells and
DNA are much simpler Called binary fission literally, splitting in
two. DNA is circular and attached to inside of cell membrane. DNA
copies itself Cell divides into two
