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Mitosis and the

Cell Cycle

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Cell Division

All cells are derived from pre-existing cells

New cells are produced for growth and to replace damaged or old cells

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All cells undergo 5 phases of the cell cycle

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All cells undergo 5 phases of the cell cycle

G1 - primary growth phase

S – synthesis; DNA replicated

G2 - secondary growth phase

M - mitosis C - cytokinesis

collectively these 3 stages

are called Interphase

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Interphase - G1 Stage

Cells mature by making more cytoplasm & organelles

Cell carries on its normal metabolic activities

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Interphase – S Stage

Synthesis stage

DNA is copied or replicated

Two identical copies of

DNA

Original DNA

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Interphase – G2 Stage

All cell structures needed for division are made (e.g. centrioles)

Both organelles & proteins are synthesized

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Mitosis

Is the division of the nucleus

Only occurs in eukaryotes

Doesn’t occur in some cells such as brain cells

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The Four Mitotic Stages

Prophase

Metaphase

Anaphase

Telophase

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Early Prophase Chromatin in nucleus condenses to form visible chromosomes

Spindle fibers form from cytoskeleton or centrioles (animal)

Sister

chromatids

(chromosomes)

Nucleolus Cytoplasm

Nuclear envelope

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Prophase Nuclear membrane & nucleolus disappear

Chromosomes continue condensing & are clearly visible

Spindle fibers (kinetochore) attach to the centromere of each chromosome

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Prophase

Nucleus & Nucleolus have disintegrated

Chromosomes

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Prophase The spindle fibers form from the microtubules in plant cells

Spindle fibers form from 2 centrioles at the centrosome in animal cells

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Metaphase

Chromosomes, attach to the kinetochore (spindle) fibers and move to the center (equator) of the cell

Pole of the Cell

Pole of the Cell

equator

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Metaphase

Chromosomes lined at the Equator

Spindle Fibers

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Anaphase

This phase occurs rapidly

Sister chromatids are pulled apart to opposite poles of the cell via kinetochore (spindle)fibers

Anaphase

Sister chromatids Are pulled

apart

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Telophase

Spindle disassembles Nuclear envelope begins to form around chromosomes

Nucleolus reappears Chromosomes reappear as chromatin

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Cytokinesis follows Telophase

The cytoplasm and organelles divide

The cell separated into two identical halves called daughter cells

Animal Cell

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Cytokinesis

Cell plate in plant cell In plant

cells, cell plate

forms at the

equator to divide

cell

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Cytokinesis

Cleavage furrow in animal cell In animal

cells, cleavage furrow

forms to split cell

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Daughter Cells of Mitosis

Have the same number of chromosomes as the parent cell from which they were formed

Are identical to each other, but smaller than parent cell

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Identical Daughter Cells

Parent Cell

Two

identical

daughter

cells

(Paired

centrioles)

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Mitosis in Onion Root Tips

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Eukaryotic Chromosomes

All eukaryotic cells store genetic information in chromosomes

Human body cells have 46 chromosomes or 23 identical pairs

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Eukaryotic Chromosomes

Each chromosome is composed of a single, tightly coiled DNA molecule

Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

Chromosome

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Compacting DNA into Chromosomes

DNA is tightly coiled around proteins called histones

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Chromosomes in Dividing Cells

Duplicated chromosomes are called sister chromatids & are held together by the centromere

Called Sister Chromatids

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Karyotype

A picture of the chromosomes from a human cell arranged in pairs by size

First 22 pairs are called autosomes

Last pair are the sex chromosomes

XX female or XY male

Chromosomes carry the information which codes for what we are and what we look like.

Widow Peak

Multi-tasking

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Types of Cell Reproduction

Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells

Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells

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Uncontrolled Mitosis

If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors

Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells