Download Chapter 8

Ch. 8 – Cellular reproduction
As a comparative / overview, organisms reproduce sexually
and/or asexually
• asexual reproduction
– Offspring are produced by a single parent, without the
participation of sperm or the transfer of genetic information
• sexual reproduction
– Transfer and integration of genetic information; i.e. fertilization
of sperm and egg produces variety of offspring
• In regards to Eukaryotic cells – unicellular organisms or
cells of multicellular organisms…
– asexual reproduction = ?
• Mitosis
– sexual reproduction = ?
• Meiosis
Cellular reproduction or division
• Asexual reproduction
– Genetic copies of
single parent cell
– “like begets like”
– “clones”
Prokaryotic asexual cellular division
• Binary fission
• Cell divides into two
– Asexually
• relatively simple
…as simple as “one,
two, three”
• Cell replicates its
genetic material
– Single chromosome
of DNA
• Copies move apart
• Growing membrane
divides the cell
Eukaryotic
cellular division
• Cells are larger
• …more complex
• Have more genes than
prokaryotes
– Grouped into multiple
chromosomes in nucleus
• before division begins
– DNA condenses into thin
loosely packed chromatin
fibers which bind to
histones (proteins) to form
chromosomes
• …before division
– Chromosomes replicate into…
– Sister chromatids joined at centromere
• Two genetic copies
• Eventually divides into two identical chromosomes
Cell cycle multiplies cells
• Most of the cycle
is preparing for
division
– Interphase
• Growth and
replication
– Cellular division
process starts with
mitosis
Prophase,
Metaphse,
Anaphase,
Telophase
Interphase
• Cell growth
– Doubling most of its
contents
– Addition of two
centrosomes in
cytoplasm
• Contain two centrioles
• Microtubule organizing
centers
Prophase of Mitosis
• Chromatin fibers coil
forming discrete
chromosomes
– Joined at waist
– Sister chromatids
• Mitotic spindle forms
– Microtubules extending
from centrosomes
• Centrosomes start to
migrate to opposite poles
Late Prophase
• Nuclear membrane
breaks down
• Spindle fibers reach
the condensed
chromosomes
– One end originating at
centrosome, other
attached to each sister
chromatid
Metaphase
• Mitotic spindle fully
formed
• Centrosomes at poles
• Chromosomes line up
at equator
Anaphase
• Centromeres split,
separating sister
chromatids
• Attatched spindle
fibers shorten
• Unattached spindle
fibers lengthen
– Push or elongate cell
• Copied chromosomes
migrate to poles
Telophase
• Reverse of prophase
• Nuclear membranes
begin to form around
chromosomes
• Mitotic spindle
disappears
• Cytoplasm prepares
to divide = cytokinesis
• …two daughter cells
http://www.youtube.com/watch?v=VlN7K1-9QB0
http://www.youtube.com/watch?v=eFuCE22agyM
Cytokinesis
• Differs in animals
and plants
• Animal:
– Ring of
microfilaments
contract
• Pinching the cell
• Like pulling a
purse-string
closed
Plant cytokinesis
• Cell wall material
forms in center
• Cell plate extends
• Cell membrane
follows
• Cell plate fuses with
cell walls