Cell Reproduction

Why Do Cells Divide???

• DNA Overload - information overload too much cell to make proteins for.

• Materials Exchange Problem – Surface Area to Volume Ratio

• Injury

• Depletion of Cells from natural death.

Human Chromosomes23 Homologous Pairs

homologous pairs= a matching pair of chromosomes, one from each parent

Chromosomes

• Number of chromosomes depends on characteristics of species

• Examples: • Humans 46 (23 pr)

Earth worm 36 (18pr)• Fly 8 ( 4 pr)

Time for cell divisiondepends on type of cellbacteria completes cycle in 22 minutes

nerve cell some only once in entire life

liver cell may take 1 year

G1 ~ intense activity & cell growthS phase ~ DNA replication ( will copy every chromosome)G2 ~ prepares for mitosis usually shortest part of interphase organelles needed for mitosis are made now

Go to Video Clips

Stages of Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase

Prophase

• Mitosis begins (cell begins to divide)

• Centrioles (or poles) appear and begin to move to opposite ends of the cell.

• Spindle fibers form between the poles.

All these cells are in prophase

Metaphase

• Chromosomes line up at the equator of the cell.

• Animal cell Plant Cell

Spindle fibers attach to the chromatids

http://www.biosci.ohio-state.edu/~plantbio/images/images%20from%20Lima/metaphase.jpg

Anaphase ~ Chromatids (or pairs of chromosomes) separate and

begin to move to opposite ends of the cell.

Animal Cell Plant Cell

TelophaseTwo new nuclei form.

Chromosomes appear as chromatin (threads rather than rods).

Mitosis ends.Animal Cell Plant Cell

CytokinesisCell membrane moves inward to

create two daughter cells – each with its own nucleus with identical

chromosomes.

Division of

Prokaryotic Cells

(binary fission)

http://www.biologycorner.com/resources/mitosis-animated.gif

MorePractice

Cell Cycle

In lab, we will be looking at the tip of a plant leaf, looking for the

different stages of mitosis

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