Chapter  10  Section  10.2

The Process of Cell Division

Chromosomes Bundles of DNA •  Must be carefully packed in

order to make sure such a large molecule is carefully divided between the two resulting daughter cells. o  Prokaryotic Cells DNA

•  Single, circular strand of DNA which floats in the cells cytoplasm (NO NUCLEI)

Chromosomes •  Eukaryotic Cells DNA

o  Much more DNA than prokaryotic cells and multiple chromosomes

o  DNA is closely associated with a protein called “histones” which forms a material called “chromatin”.

o  Usually the chromosomes you see are “duplicated” chromosomes with supercoiled chromatin.

o  These chromosomes make it possible to separate DNA precisely during cell division.

Cell  Cycle Cell grows, prepares for cell division, and divides to form two new daughter cells. •  Prokaryotic Cell Cycle:

is a regular pattern of growth, DNA replication and cell division known as “binary fission”. (form of asexual reproduction)

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127 Lesson 10.2 10.2 Binary Fission

Cellmembrane

DNA

DNA duplicates.

Cell membraneindents.

Cell divides;two new cells form.

Cell  Cycle •  Eukaryotic Cell Cycle

o  Consists of 4 distinct phases: G1 (Gap 1), G2 (Gap 2), S (Synthesis), M (Mitotic)

•  The first 3 are often called “Interphase”

o  G1 (Gap 1): Cells do most of their growing during this phase and synthesize new proteins and organelles

o  S (Synthesis): New DNA is synthesized when the chromosomes are replicated.

Cell  Cycle •  Eukaryotic Cell Cycle

o  G2 (Gap 2): shortest and is used to create many of the organelles necessary for cell division.

o  M (Mitotic): follows interphase and produces the two daughter cells. Normally involves:

•  Mitosis: division of the nucleus

•  Cytokinesis: division of the cytoplasm.

The Eukaryotic Cell Cycle o  The eukaryotic cell cycle consists of four phases: G1, S, G2, and M.

o  Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.

many of the organelles and molecules required for cell division are produced.

cells increase in size and synthesize new proteins and organelles.

Prophase o  During prophase, the first phase of

mitosis, the duplicated chromosome condenses and becomes visible.

o  The centrioles move to opposite sides of nucleus and help organize the spindle.

o  The spindle forms and DNA strands attach at a point called their centromere.

o  The nucleolus disappears and nuclear envelope breaks down.

M Phase (Mitosis)

Metaphase o  During metaphase, the second phase

of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.

o  The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.

Anaphase o  During anaphase, the third phase of

mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.

o  The chromosomes separate into two

groups near the poles of the spindle

Telophase o  During telophase, the fourth and final

phase of mitosis, the chromosomes spread out into a tangle of chromatin.

o  A nuclear envelope re-forms around

each cluster of chromosomes.

o  The spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus

Cytokinesis o  In animals the cell membrane is drawn in until the cytoplasm is pinched into two equal parts.

o  Each part contains its own nucleus and organelles.

o  In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall.

o  Instead, a cell plate forms between the divided nuclei that develops into cell membranes.

o  A cell wall then forms in between the two new membranes.

Cyclins •  The cell cycle is controlled by

regulatory proteins both inside and out. o  These proteins regulate the timing of the cell

cycle. •  Internal regulators are proteins that respond to

events inside a cell. They allow the cell cycle to proceed only once certain processes have happened inside the cell.

•  External regulators are proteins that respond to events outside the cell. They direct cells to speed up or slow down the cell cycle.

•  Growth factors are external regulators that stimulate the growth and division of cells. They are important during embryonic development and wound healing.

o  Cancer is a disorder in which defects in genes cause body cells to lose the ability to control cell growth due to many causes such as smoking, radiation, defective genes, and viral infection.

o  Cancer cells divide uncontrollably to form a mass of cells called a tumor.

o  A benign tumor is noncancerous. It does not spread to surrounding healthy tissue.

o  A malignant tumor is cancerous. It invades and destroys surrounding healthy tissue and can spread to other parts of the body. The spread of cancer cells is called metastasis.

If Cell Division doesn’t go quite as planned