Chapter 8 Part 1

Mitosis

Cell Division and Reproduction

Chromosomes become visible during cell division

A karyotype displays the chromosomes

• Karyotype– Display of the

chromosomes– 23 pairs of chromosomes– 46 total chromosomes– One member of each pair

comes from the father, the other member comes from the mother

• Autosomes– Have nothing to do with gender– 22 pairs

• Sex chromosomes– Determines gender– XY is male– XX is female

• Homologous pair– Pair of autosomal chromosomes– Look alike– Carry genes for the same trait (earlobe, hairline,

finger length)

• Sister chromatids– Duplicated chromosome required for mitosis

• Centromere– Holds together sister chromatids

• Kinetochores– Protein complexes at centromere where spindle fiber

attaches during cell division

The eukaryotic cell cycle has a set series of stages• Cell cycle

– Series of stages of cell growth and division

• Interphase– Time between cell division

• G1 Stage– Recovery from division– Decides whether to divide or not

» Enters G0 if it is not going to divide where it will continue normal processes

– If it is going to divide, it doubles in size, double organelles, accumulates molecules needed for DNA synthesis

• S Stage– DNA replicated resulting in sister

chromatids

• G2 Stage– Organelle replication continues– Makes proteins (microtubules)

needed for cell division

M stage (mitosis)• Cell division• Chromosomes

divided between 2 cells

• Cytokinesis– Division of cytoplasm

Mitosis maintains the chromosome number

Following mitosis, daughter cells have the same chromosome count as the parent cell

• Parent cell– Original cell

• Daughter cells– 2 new cells

• When cells enter M stage, it has sister chromatids (duplicated chromosomes)

• Animal cell are diploid (2n) throughout mitosis (chromosomes are in pairs)

• Some protists and fungi are haploid (n) before and after mitosis

The spindle apparatus• Centrosome

– Divides at the start of nuclear division

– Produce spindle fibers, which assist separation of the chromatids as they move to opposite poles

Mitosis has a set series of phases

Early prophase• Centrosomes divided• Chromatin condensing into chomosomes• Nuclear envelope fragmentingProphase• Nucleolus disappeared• Duplicated chromosomes (sister chromatids)

visible• Centosomes begin moving apart• Spindle is in the process of forming

Early metaphase

• Each duplicated chromosomes attached to the spindle apparatus

• Spindle fibers stretch from each pole

Metaphase

• Centromeres of duplicated chromosomes are aligned at equator

• Kinetochores attach sister chromatids to spindle fibers that come from opposite poles

Anaphase

• Sister chromatids part and become daughter chromosomes that are pulled toward the poles

Telophase

• Daughter cells are forming

• Nuclear envelopes and nucleoli reappear

• Chromosomes become chromatin

Contribution of the Cell Cycle to Human Health

Cell division allows a fertilized egg to develop into a newborn and is also important in repairing damage to your body like broken bones and cuts.

Cytokinesis divides the cytoplasm

Animal cell cytokinesis• Cleavage furrow forms

between the two daughter cells

• Furrow deepens when the contractile ring forms between cells and continues to tighten

• 2 independent daughter cells result

Plant cell cytokinesis

• A new plasma membrane (cell plate) comes between the new cells

• The new membrane releases molecules that form a new cell wall between the new cells

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