Cell Cell Replication:Replication: Cell CycleCell Cycle

Chapter 10

* Cells must divide for the following reasons:

1. So that an organism can grow

2. So that an organism can develop

3. Repair

I. Bacteria cells undergo binary fission to divide. This is a form of asexual reproduction, where the parent passes exact copies of the DNA to its offspring (Remember- Bacterial cells are prokaryotes!)

II. Eukaryotic Cells must form chromosomes before cell division.

A. Chromosome Structure

Nucleus (DNA is found here)

DNA is found on chromosomes inside the nucleus.

Chromotids – Where genes are located.

Centromere-

Where the 2 chromatids are attached.

One Gene. Most chromosomes have several hundred genes.

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Before cell division can take Before cell division can take place, each chromosome place, each chromosome must copy itself:must copy itself:

This chromosome now has sister sister chromatids.chromatids. They are identical in genetic material to each other.

One chromosome that has One chromosome that has copied its DNA.copied its DNA.

• GG11 – Rapid Cell Growth; – Occupies most of the

cell’s life.

• S S DNA is copied.• GG22 Microtubules are

assembled• MitosisMitosis Nucleus

divides• CytokinesisCytokinesis

Cytoplasm divides

•Mitosis and Cytokinesis produce new cells that are identical to the original cell. Allows cells to grow and replace damaged tissues.

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IV. The Cell Cycle is Controlled!A. Proteins act as signals that can permit or

delay the next phase of the cell cycle.

Checkpoints in the Cell Cycle:

1. G1 If the cell is healthy, then its DNA

will copy.2. G2 DNA

replication is checked. If it occurred correctly, then mitosis is triggered.

3. Mitosis Signals beginning of G1.

V. CancerA. Occurs when a cell loses

control of the cell cycle. The cell barrels thru the checkpoints.

VI. VI. MitosisMitosis Division of Division of the the

NucleusNucleus

InterphaseInterphase• This is the time when This is the time when

the genetic material is the genetic material is actually being used to actually being used to govern or regulate cell govern or regulate cell activity. Chromosomes activity. Chromosomes are not visible during are not visible during Interphase.Interphase.

ProphaseProphase• Chromosomes Chromosomes

become visible. become visible. (Chromosome is (Chromosome is already copies).already copies).

• Nuclear envelope Nuclear envelope dissolves. dissolves.

MetaphaseMetaphase• Chromosomes Chromosomes

line up along line up along equator.equator.

AnaphaseAnaphase• Centromeres Centromeres

divide.divide.• Chromatids (now Chromatids (now

called called chromosomes) chromosomes) move toward move toward opposite poles.opposite poles.

TelophaseTelophase• Nuclear envelope Nuclear envelope

forms at each pole. forms at each pole. • Chromosomes Chromosomes

uncoil. uncoil. • Spindle dissolves.Spindle dissolves.• Cytokinesis begins. Cytokinesis begins.

2 genetically 2 genetically identical identical daughter daughter

cells.cells.

Review

I. Mitosis DNA Replication & Division = 2 daughter cells genetically identical to the parent cell. Video of Mitosis

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Body Cell

II. Meiosis Reduction Division; Four daughter cells genetically different from the parent cell.

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23 n

23 n 23 n23 n

23 n

Parent Reproductive Cell

III. Phases of Meiosis A round of DNA replication occurs before stage I.

• Begin with a diploid cell. • Each chromosome seeks out

its corresponding homologous chromosome to form a tetrad.

• Each Tetrad contains 4 chromatids.

Stage I Stage I Meiosis I :Meiosis I : Prophase Prophase II

• While together, homologous chromosomes exchange genetic information during a process called crossing over.

Ex.

AB

CB

C

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A

E EF F

Stage II Meiosis I : Metaphase I

• Homologous chromosomes (tetrads) line up across the center of the cell.

Stage III Meiosis I : Anaphase I

• Spindles pull the tetrads apart.

Stage IV Meiosis I : Telophase I &

Cytokinesis •At the end of telophase, cytokinesis occurs. •2 new daughter cells that are haploid and genetically different from the parent cell have formed.

Review of Meiosis I

• Meiosis Practice

Stage V Meiosis II : Prophase II

• A new spindle forms around the chromosomes.

Stage VI Meiosis II : Metaphase II

• Chromosomes line up at the equator.

Stage VII Meiosis II : Anaphase II

• Centromeres divide.• Sister chromatids split (now called

chromosomes) and move to opposite ends of each cell.

Stage VIII Meiosis II : Telophase II

• A nuclear envelope forms around each set of chromosomes.

• The result: 4 haploid daughter cells that are genetically different form the parent cell.

Review of Meiosis II

• Meiosis II Practice

Meiosis In Meiosis In MalesMales vs. vs. FemalesFemales

SpermatogeneSpermatogenesissis

OogenesisOogenesis

Genetic VariationGenetic Variation

• 3 events give rise to genetic variation in sexually reproducing individuals.

1)1) Crossing OverCrossing Over Homologous chromosomes exchange genes.

2)2) Independent AssortmentIndependent Assortment which cell each homologous chromosome will end up in is random.

3)3) Random FertilizationRandom Fertilization The random mating of organisms in nature.

Genetic Variation Speeds Genetic Variation Speeds Up Evolution!!Up Evolution!!

It offers new combinations It offers new combinations of traits that the of traits that the environment can choose environment can choose for or against.for or against.