Major Concepts to Review for A.P. Exam
Cell Reproduction
DNA is packaged in the nucleus
- histone proteins necessary for first coiling
= nucleosomes (looks like beads on a string)
- three or four additional levels of coiling
produce the thick short structure called a chromosome, visible
under the light microscope (only the most powerful electron
microscopes can "see" nucleosomes
- Thickness changes from 10 nanometer nucleosome
to a metaphase chromosome = 1000 nm (an increase in thickness of
100)
The Cell Cycle
Mitosis
- Prophase - most events including DNA
condenses, nuclear membrane is disassembled, spindle apparatus is
assembled (in animals centrioles divide and migrate to opposite
poles.
- Metaphase - chromosomes line up due to
multiple microtubules connected at the centromere/kinetochore
region
- Anaphase - centromere splits and daughter
chromatids are toughed apart moving to opposite poles
- Telophase - generally opposite of
prophase
- Cytokinesis - 2 cells half the size of the
original cell emerge as a cleavage furrow (animals) pinches in or
a cell plate forms midway between the poles of the old cell
(plants)
Mitosis - Advantages
growth by easily adding to the number of
cells
repair - would healing
maintenance of cell count by replacing old
cells (red and white blood cells for example)
Meiosis
- converts diploid cell into haploid
condition
- involves 2 nuclear divisions: meiosis I and
Meiosis II
- meiosis I reduces chromosome # in half (the
reduction division). Homologous chromosomes are separated in
anaphase I. Otherwise steps similar to mitosis.
- meiosis I involves crossing over of homologous
chromosomes in prophase I - shuffling of genes increases variation
in the next generation (natural genetic recombination)
- meiosis II identical to mitosis but results in
4 cells
- meiosis differs between males and
females.
Meiosis - purpose
necessary for sexual reproduction because
2 haploid cells will unite to from a diploid zygote
meiosis results in haploid cells with greater
variety because of crossing over events in prophase I - some
variations may be advantageous.
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