Chapter 4 Cell Division and Reproduction

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Cell Division and Genetic Material

Genetics: Field of bio involving the study of how genetic info is passed from one generation of organisms/cells to the next generation.

The Cell Theory:

All living things are composed of one or more cells

Cells are smallest units of living organisms

New cells come only from pre-existing cells by cell division

All new cells = product of existing cells, following traits must be passed from one cell; parent cell to new cells; daughter cells

Traits are passed through genetic material in form of (DNA)

When a cell divides, each new cell receives genetic info from the parent cell.

The Cell Cycle

Cells reproduce through controlled growth and division in a process called the "cell cycle"

Somatic Cells: body cells of plants and animals; excluding reproductive cells, go through cell cycles

Each time cell goes through one complete cycle, it becomes 2 cells.

In multi cellular cells there are 3 functions of cell division

Growth of organism

Repair of damaged tissues and organs

Maintenance/replacing of dying/dead cells

The duration of cell cycle varies b/c it depends on type of cell

For example:

In flies, cell cycle takes 8 mins

Liver cells, take over a year

For most healthy actively dividing animal cells takes about 12-24 hours

Stages of the Cell Cycle

Inter-phase: Cell carries out its normal functions, grows, and makes copies of its genetic material in prep for next stage of the cycle

Mitosis: Cell`s nucleus and genetic material divide

Cytokines: Begins near the end of mitosis - division of the cell cytoplasm and creation of a new cell.

Proper functioning of the cell is essential for organism to develop normally and remain healthy.

Specific points called cell cycle checkpoints monitor growth to ensure the cycle continues when it should

Complex network of signals in the cell occurs to check regulation of the cell.

Something interfering with these signals implies possible uncontrolled growth

Ex. Cancer is the result of uncontrolled rapid cell division.

The cancerous cells progress quickly from one cell division to the next, resulting in A LOT of cells called a tumor.

Interphase

Cell grows, develops into a mature, functioning cell, copies its DNA, and prepares for division.

Interphase has 3 phases : G1, S, G2

G1

major growth period, cell synthesizes many new molecules in prep for next phase in the cycle

S (synthesis)

Cellular DNA is copied/replicated.

DNA exists as uncondensed fibers called Chromatin

G2 (Growth 2)

Cell synthesizes more molecules prior to mitosis and cell division.

Mitosis (Prophase, Metaphase, Anaphase, and Telophase)

The copied genetic material separates and the cell prepares to split into 2 cells.

Key activity is to accurately separate the cell`s replicated DNA

This lets the cell`s genetic info to pass into the new cells intact, resulting in 2 genetically identical cells.

Prophase

Cell`s chromatin condenses into chromosomes; a structure in the nucleus containing DNA.

Since the DNA was copied during interphase, each chromosome in prophase exists as 2 copies of one chromosome

Two chromosome arms are called sister chromatids (one of the two chromosomes that are genetically identical and held together at the centromere) (region where 2 sister chromatids are held together in a chromosome)

The nuclear membrane breaks down, and the nucleolus disappears.

Spindle fibres; made of hollow tube like structures called microtubules are formed from the centrosomes as they move apart to opposite poles of the cell.

The fibres and centrosomes are called spindle apparatus which moves and organizes the chromosomes during mitosis

Metaphase

Spindle fibres guide chromosomes to the equator of cell.

Spindle fibres from opposite poles attach to the centromere of each chromosome

Anaphase

Each centromere splits apart and the sister chromatids separate from each other

The separated sister chromatids are referred as chromosomes

Spindle Fibres shorten, pulling chromosomes to opposite poles of the cell.

At the end of Anaphase, 1 complete set of chromosomes has been gathered at each pole of the cell.

Telophase

Chromosomes have reached the opposite poles of the cell.

Chromosomes start to unwind into strands of less visible chromatin.

Spindle fibres break down, nuclear membrane forms around new set of chromosomes and nucleolus forms within each new nucleus

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