Cell Growth & Division Chapter 10

10-1 Cell Division = cell reproduction Limits to Cell Growth 2 main reasons that cells divide: 1. The larger a cell becomes → the more demands it puts on the DNA of the cell 2. Has difficulty getting nutrients (food, O 2, H 2 O) in & waste out Before cell division can happen, all DNA info must be replicated (copied)

3 Types of Cell Division A.Binary Fission – a form of asexual reproduction 1.Performed by bacteria 2.Produces identical offspring 3.Single parent passes exact copies of its DNA its DNA 4.Two Stages a.DNA is copied b.Cell divides

B.Mitosis division of cell nucleus 1.Is asexual reproduction 2.Used for growth, repair & development 3.Produces identical new cells to original parent cell 4.Chromosome number is the same as the parent cell number

C.Meiosis – division of cell nucleus in gametes 1.Is sexual reproduction 2.Produces 4 gametes – reproductive cell = sperm or egg 3.Chromosome number is ½ of the parent cell number

Before cell division, DNA + proteins coil into chromosomes Before cell division, DNA + proteins coil into chromosomes Chromosome = 2 chromatids ( exact copies of DNA) attached at the centromere Chromosome = 2 chromatids ( exact copies of DNA) attached at the centromere →Only visible during cell division Centromere – area where chromatids of a chromosome are attached Centromere – area where chromatids of a chromosome are attached Gene – sequence of DNA that determines a trait Gene – sequence of DNA that determines a trait Trait – specific characteristic that varies from 1 individual to another Trait – specific characteristic that varies from 1 individual to another Genes are located on chromosomes in the cell nucleus Genes are located on chromosomes in the cell nucleus Each organism has a characteristic number of chromosomes Each organism has a characteristic number of chromosomes  Ex: Humans have 46 (23 pairs) chromosomes

10-2 Cell Cycle Cell Cycle – series of events that cells go through as they grow & divide Interphase – longest part of the cell cycle 1.G 1 phase – first growth phase a.Most of growth is done here rapidly b.Occupies major portion of cell’s life c.Cells that are not dividing remain in G 1 2.S phase – synthesis phase a.DNA is copied b.Key proteins made 3.G2 phase – second growth phase a.Preparation for the nucleus to divide b.Organelles & other molecules needed replicated c.Microtubules are assembled 4.Mitosis- division of nucleus 5.Cytokinesis – cytoplasm division

Mitosis & Cytokinesis Spindles – cell structures made of centrioles & microtubules 1.Function: separate chromosomes & chromatids 2.Spindle fibers attach to centromere 3.Drag chromosomes to opposite sides of cell 4. hill.com/olcweb/cgi/pluginpop.cgi?it=swf::53 5::535::/sites/dl/free/ /120073/bio 14.swf::Mitosis%20and%20Cytokinesis hill.com/olcweb/cgi/pluginpop.cgi?it=swf::53 5::535::/sites/dl/free/ /120073/bio 14.swf::Mitosis%20and%20Cytokinesishttp://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::53 5::535::/sites/dl/free/ /120073/bio 14.swf::Mitosis%20and%20Cytokinesis

Mitosis – continuous process w/ 4 stages 1.Prophase: a.Chromosomes coil b.Spindle fibers form 2.Metaphase- chromosomes line up in center of cell 3.Anaphase a.Centromere divides b.Chromosomes move to opposite sides of cell 4.Telophase a.Chromosomes uncoil b.Spindle fiber disappears Product: 2 (two) new nuclei

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Cytokinesis – occurs at the same time as telophase In animals, cell membrane encloses each nucleus & cell parts → original cell pinches in 2. In plants, cell plate is formed across the middle of the cell & new cell wall forms on both sides of the plate. End Results:  Two genetically identical cells  Cells equal in size  Each with ½ of cytoplasm & organelles  Chromosome number = # of chromosomes in the original cell

11-4 Meiosis- a process of cell division that cuts the chromosome # in ½ producing gametes or spores. Requirements of reproduction: 1.Each organism must inherit a single copy of every gene from each of its parents 2.An organism produces gametes = sperm or egg

Chromosome Number Fruit fly example  Adult fruit fly body cell has 8 chromosomes → 4 from the father; 4 from the mother  These chromosomes are homologous – have a corresponding chromosome from opposite-sex parent which is  same size & shape and carry the same type of info.  Cell w/ both sets of homologous chromosomes & 2 complete sets of genes is 2n = Diploid Fruit fly diploid # = 8  Gametes are haploid (N) – contain only 1 set of chromosomes & 1 set of genes Fruit fly gamete has 4 chromosomes. N = 4

Meiosis 1.Involves 2 divisions of the nucleus – Meiosis I & Meiosis II Each division has 4 stages 2.Starts w/ a diploid cell 3.Like mitosis, chromosomes replicate during the S phase of Interphase 4.Meiosis 1 is similar to Mitosis

STEPS of Meiosis Meiosis I 1.Prophase I a.Chromosomes Coil b.Homologous Chromosomes pair to form a tetrad – 4 chromatids c.Crossing over can occur – portion of chromatid breaks off & exchange w/ corresponding portion on homologous chromosomes *gives new combinations of traits 2.Metaphase I – Pairs of homologous chromosomes line up in center of cell 3.Anaphase I - Chromosomes separate & go to opposite sides of cell 4.Telophase I a.Cytoplasm divides b.Each new cell contains 1 chromosome from each pair of homologous chromosomes c.Two cells that have shuffled chromosomes immediately enter next stage

STEPS of Meiosis (continued) Meiosis II - No DNA replication 5.Prophase II - New spindle fibers form around the 2 chromatids in each cell 6.Metaphase II - Chromosomes (each 2 chromatids) line up in center of cell & attach at the centromere to spindle fibers 7.Anaphase II - Centromeres divide & chromatids go to opposites sides of the cell 8.Telophase II a.Spindle fibers disappear b.Produces 4 haploid cells = gametes Male → 4 sperm (N) Female → 1 egg (N) Cytokinesis – cytoplasm & organelles divide

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Genetic Variation – new genetic combinations → is essential for evolution  As variation increases, evolution increases  3 mechanisms 1.Independent assortment – random distribution of homologous chromosomes a.Each pair of chromosomes separate independently b.In humans, 1 original cell can produce ~ 8 million different combinations 2.Crossing over – which occurs during Prophase I 3.Random fertilization a.Zygote (fertilized egg) is formed by joining of egg & sperm b.Each gamete is produced independently which makes the possible outcomes - > 64 trillion

Reproduction – the process of producing offspring 1.Two types : Asexual and sexual 2.Type determines the amount of similarity to parents & siblings Asexual reproduction 1.Single parent passes copies of all its genes to each offspring 2.No combining of haploid cells 3.Produces clones – individuals genetically identical to parent 4.Used by prokaryotes & many eukaryotes 5.Advantage: only need 1 parent 6.Disadvantage: less variation → more susceptible to change

Sexual Reproduction 1.2 parents each form gametes (N) which join to form offspring 2.Traits of offspring come from both parent 3.Offspring not identical to either parent 4.Used by eukaryotes 5.Advantage: Creates more variation; more adaptable 6.Disadvantage: need 2 parents