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=VlN7K1-9QB0http://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