Unit 3: Mitosis and Meiosis

The Cellhttp://learn.genetics.utah.edu/content/begin/cells/scale/Unit 3: Mitosis and Meiosis

Chapter 8: How Cells Reproduce1Cells: from largest to smallest

Cell smallest unit of lifeNucleus protects genetic materialDNA macromolecule that contains the genetic codeChromosome strand of DNAGene segment of a chromosome that codes for a protein or trait

Three Questions to Keep in MindUnderstanding cell division starts with three questions:

What kind of information guides inheritance?How is that information copied inside a parent cell before being distributed to each of its daughter cells?What kinds of mechanisms parcel out the information to daughter cells?Mechanisms of Cell DivisionReproduction produces a generation of individuals like their parentsCell division is the bridge between generationsEach daughter cell receives:

Therefore, before cells are able to reproduce, there has to be a division of the nucleus and its DNA.

Eukaryotes and ProkaryotesEukaryotic cells undergo _________ and/or __________These lead to the distribution of DNA to new nuclei in forthcoming daughter cellsAnother mechanism divides cytoplasm

Prokaryotic cells reproduce asexually by a different mechanism called prokaryotic fissionMitosis and MeiosisBoth mitosis and meiosis are eukaryotic nuclear division mechanismsMitosis is used by multicelled organisms for growth, which occurs through the repeated division of somatic cellsMeiosis occurs only in reproductive cells that divide to form gametes or sporesGametes in humans/other mammals: egg and spermSpores: fungi, plants, and many kind of protists

Somatic cells: body cellsGamete: reproductive cell

Cell Division Mechanisms

Chromosome StructureChromosome: a molecule of DNA complexed with proteinsPrior to cell division, each threadlike chromosome is duplicated to form two ________________ held together by a _______________________: proteins that tightly bind to DNA and cause spooling into structural units called nucleosomes, which prevent tangling______________ are the smallest unit of organization

Structure of Condensed Chromosomes

Figure 8.4, pg 127

a One duplicated human chromosome in its most condensed form.centromereFig. 8.4a, p.127

Fig. 8.4b, p.127

Fig. 8.4d, p.127Chromosome StructureThe constricted region where two sister chromatids attach is the _______________Remain attached until late in mitosis (or meiosis)During cell division, a ________________ forms at the centromereKinetochore: the binding sites for microtubulesThis is the region where duplicated chromosomes will attach to the microtubules of the spindle during nuclear division

Figure 8.3, pg 126ChromosomesImportant things to remember about chromsomes:Individuals of a species have a characteristic number of chromosomes in each cell

Chromosomes differ in length and shape, carry different portions of cells hereditary information

Mechanisms divide information between daughter cells, along with enough cytoplasm for each cell to operate on its own

The Cell CycleLife cycle: the sequence of stages through which individuals of a species pass during their lifetimeThe cell cycle is a recurring sequence of events that extends from the time of a cells formation until each division is completedBegins when a new daughter cell forms by mitosis and cytoplasmic divisionEnds when that cell dividesIncludes __________________, _________________________ , and ______________Eukaryotic Cell Cycle

Figure 8.5, pg 128______________Most cellular activities occur in interphaseAbout 90% of a cells existence is spent in interphaseMitosis occupies only a small portion During interphase:The cells mass increasesCytoplasmic components approximately double in numberAND the DNA is doubledSome cells are arrested in interphase and usually never divide again

Stages of InterphaseThe control of cell division resides in these three stages of interphase:G1: (gap) Interval during which cell grows in mass, doubles the number of cytoplasmic components, and assembles most of the carbs, lipids, and proteins that are needed by the cell and for exportS: (synthesis) the DNA and histones are copied through the process of DNA replicationG2: (gap) Interval during which further protein synthesis drives the cell toward mitosis as it prepares for division

Chromosome NumberAll somatic cells of a particular species have the same number of chromosomesHuman cells have ______chromosomesChromosomes come in pairs one from each parentThese pairs carry genes for the same traitChromosome number (n) tells how many of each type of chromosome is present in a cellBody cells are _____________(2n), which means they have two of each kind of chromosomeHuman Chromosomes: ________

Mitosis and Chromosome NumberMitosis maintains parental chromosome number from one generation to the next__________ __________ composed of two sets of microtubules divides sister chromatids

Figure 8.6, pg 129MitosisMitosis: a nuclear division mechanism that maintains chromosome numberMitosis proceeds in four stages:1)2)3)4)CentrosomesMost animal cells have a _____________, a region near the nucleus that will organize microtubules while they are formingCalled a Microtubule Organizing Center (MTOC)Usually include two pairs of barrel-shaped centriolesThe centromsome is duplicated just before prophase

Plants and fungi use other structures as MTOCs____________Early Prophase:Chromosomes start to condense and become visible as rodlike units, each consisting of two sister chromatids

Late Prophase:Chromosomes continue to condenseMicrotubules move one centrosome, with one pair of centrioles, to opposite poles of the cellNuclear envelope begins to disintegrateMicrotubules form a bipolar spindleFigure 8.7b and c, pg 130

Prophase:

Transition from ________to _________Microtubules of the spindle extend from the centrioles and attach to the centromeres (kinetochore area) of the duplicated chromosomesThe transition to metaphase occurs as chromosomes begin an orderly arrangementSister chromatids are attached separately to microtubules from opposite poles

Transition to Metaphase

______________The cell is in metaphase when all the chromosomes are aligned at the cells equator halfway between the polesChromosomes are in their most tightly condensed formFigure 8.7e, pg 130e Metaphase:chromosomes line up in the middle________________During anaphase, the cells migrate to opposite polesThe kinetochores of sister chromatids separate and move toward opposite polesMicrotubules attached to the centromeres _______ and pull the chromosomes toward the polesOther microtubules that overlap at the spindles midpoint __________ past each other to push the two spindle poles apart__________ _____________drive movementsOnce separated, each chromatid is now an independent chromosomeAnaphase:

Figure 8.7f, pg 130______________Telophase begins when the chromosomes reach the two polesEach half of the cell now contains two clusters of chromosomes that are identical and equal in numberThe chromosomes decondense and return to the threadlike form typical of interphaseThe nuclear envelope forms from the fusion of small vesiclesWe now have two new nuclei that each have the parental chromosome numberMitosis is complete!Telophase:

Figure 8.7g, pg 130After mitosis and cytoplasmic division:_______________________

Mitosis divides the ___________, NOT the _________________Figure 8.7h, pg 130