Cell Division

Chapter 10: Cell Growth and DivisionSection 11.4: MeiosisCell Division1Do you remember any of the eight characteristics of living things?Living things are based on a universal genetic code (DNA)Living things grow and developLiving things respond to their environment (stimulus)Living things reproduceLiving things maintain a stable internal environment (homeostasis)Living things obtain and use material and energy (metabolism)Living things are made up of CELLSTaken as a group, living things evolve over time2Plant vs. AnimalCell wall and cell membraneLarge central vacuoleChloroplast (photosynthesis) and mitochondria (cellular respiration)

Only a cell membraneSmaller vacuolesOnly mitochondria (cellular respiration)LysosomesCentrioles used in cell divisionFlagella

Chromatin and Chromosomes:

Inside the nucleus are fine strands of chromatin = a complex of DNA bound to proteinChromatin coil up and become densely packed, forming chromosomesChromosomes are visible under a microscope when a cell divides

4Number of chromosomes in a human body cell?

23 pairs of chromosomes = 46 chromosomes total23 from mom and 23 from dadCells:Basic unit of structure and function in living things.Cells with a specific structure and function and are found in multi-celled organisms.Examples: skin cells, blood cells, brain cells, bone cells, liver cell, nerve cells, muscle cells, etc.

Brain cellsBlood cellsLiver cells6Where are chromosomes in eukaryotic cells?

NUCLEUSCYTOPLASMTwo categories of cellsProkaryoticEukaryotic-No Nucleus-Nucleus-Smaller Ribosomes less complex-Less complex-DNA is X shaped- Ribosomes larger and complex-Membrane bound organelles-Complex-Cell wall (plants and bacteria)-DNA is circular-Cell membrane-DNA-Cytoplasm-Ribosomes-Multicellular-Living things-Unicellular0.1-10m10-100mVocabulary:Asexual Reproduction Sexual Reproduction Mitosis Meiosis Diploid Haploid

Chromatin Chromatid Centromere Histone Nucleosomes 9Asexual Reproduction:The production of genetically identical offspring from a single parent

10Sexual Reproduction:Offspring are produced by the fusion of two sex cells one from each of two parents. These fuse into a single cell before the offspring can grow.

11Mitosis: Division of the nucleus of a eukaryotic cell Followed by cytokinesis division of the cytoplasm The two daughter cells are identical to the original cell

12Meiosis:Process that produces gametes from a diploid cell. A reductive division of the nucleus that produces four haploid gametes.

13Diploid: Cells having two sets of chromosomes2N = 46Examples: All human body cellsExcept reproductive cells (sperm and egg)

14Haploid:Cells containing only one set of chromosomesN = 23

15Chromatin:DNA and protein (histones) in the nucleus of a non-dividing cell

16Chromatid:One of the two identical parts of a replicated chromosome

17Centromere:Point of attachment between sister chromatids

18Histone:Protein molecule that DNA wraps around during chromosome formation

19Nucleosomes:The beadlike structures formed by DNA and histone molecules

20Section 10.1Cell Growth, Division, and Reproduction21THINK ABOUT ITWhen a living thing grows, what happens to its cells?

What are some of the difficulties a cell faces as it increases in size?

Bozeman Science - Why Are Cells Small22Limits to Cell SizeThere are 2 main reasons why cells do not grow indefinitely:Larger cells place more demands on their DNAWhen a cell is small, the information stored in DNA is able to meet all of the cells needsIts like putting a Volvo engine in a Hummer just doesnt have the power to make it go.

23Limits to Cell Size2. Larger cells cant move enough nutrients and waste across the cell membraneFunction of the cell membrane: help exchange materials between outside and inside of the cell.A huge cell is going to need lots of food, water, and oxygen and produce lots of wastes that would have to travel through the cell and across the membrane.

24Limits to Cell SizeThe larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane.

25Information Overload Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access.

A growing cell makes greater demands on its genetic library. If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

26Exchanging MaterialsFood, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way.The rate at which this exchange takes place depends on the surface area of a cell.

27Exchanging MaterialsThe rate at which food and oxygen are used up and waste products are produced depends on the cells volume.The ratio of surface area to volume is key to understanding why cells must divide as they grow.

28Ratio of Surface Area to VolumeImagine a cell shaped like a cube... As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.

29Traffic ProblemsTo use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out.

Similarly, a cell that continues to grow would experience traffic problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.

30Division of the CellBefore a cell grows too large, it divides into two new daughter cells in a process called cell division.Before cell division, the cell copies all of its DNA.It then divides into two daughter cells. Each daughter cell receives a complete set of DNA.Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.

31Cell Division and ReproductionAsexual ReproductionSexual ReproductionA single parentGenetically identical offspringProkaryotic and eukaryotic single-celled organisms and many multicellular organismsSimple, efficient, & effective way for an organism to produce a large number of offspring.

Fusion of two sex cells one from each of two parentsGenetically diverse offspringMost animals and plants, and many single-celled organismsGenetic diversity helps ensure survival of species when environment changes32Section 10.2The Process of Cell DivisionCell Cycle and Mitosis (6:20)33ChromosomesThe genetic information that is passed on from one generation of cells to the next is carried by chromosomes.Every cell must copy its genetic information before cell division begins.Each daughter cell gets its own copy of that genetic information.Cells of every organism have a specific number of chromosomes.

34Prokaryotic ChromosomesProkaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm.

Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cells genetic information.

35Eukaryotic ChromosomesIn eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.Chromatin is composed of DNA and histone proteins.DNA coils around histone proteins to form nucleosomes.The nucleosomes interact with one another to form coils and supercoils that make up chromosomes.

36The Prokaryotic Cell CycleBinary fission is a form of asexual reproduction during which two genetically identical cells are produced. For example, bacteria reproduce by binary fission.

Binary Fission (1:02)37The Eukaryotic Cell CycleThe eukaryotic cell cycle consists of four phases: G1, S, G2, and M.Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.

Eukaryotic Cell Cycle | Biology | Genetics (4:19)38G1 Phase: Cell GrowthIn the G1 phase, cells increase in size and synthesize new proteins and organelles.

39G0 PhaseCells that leave the cell cycleDo NOT copy their DNA Do NOT prepare for cell divisionExample: cells of the central nervous system

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S Phase: DNA ReplicationIn the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.41

G2 Phase: Preparing for Cell DivisionIn the G2 phase, many of the organelles and molecules required for cell division are produced.McGraw Hill Control of Cell Cycle

McGraw Hill - How the Cell Cycle Works42

M Phase: Cell DivisionIn eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.

Mitosis is the division of the cell nucleus.

Cytokinesis is the division of the cytoplasm.Mitosis (1:29)Eukaryotic Cell Cycle (3:45)43Important Cell Structures Involved in MitosisChromatid each strand of a duplicated chromosome

Centromere the area where each pair of chromatids is joined

Centrioles tiny structures located in the cytoplasm of animal cells that help organize the spindle

Spindle a fanlike microtubule structure that helps separate the chromatids44ProphaseDuring prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. The centrioles move to opposite sides of nucleus and help organize the spindle.The spindle forms and DNA strands attach at a point called their centromere. The nucleolus disappears and nuclear envelope breaks down.This is the longest stage of mitosis.

45MetaphaseDuring metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.This is the shortest phase of mitosis.

46AnaphaseDuring anaphase, the third phase of mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.The chromosomes separate into two groups near the poles of the spindle.

47TelophaseDuring telophase, the fourth and final phase of mitosis, the chromosomes spread out into a tangle of chromatin. A nuclear envelope re-forms around each cluster of chromosomes.The spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.Chromosomes uncoil.

Stages of Mitosis (30 s)48CytokinesisAnimal CellsPlant CellsThe cell membrane is drawn in (cleavage furrow)until the cytoplasm is pinched into two equal parts.Each part contains its own nucleus and organelles.

In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall.A cell plate forms between the divided nuclei that develops into cell membranes.A cell wall then forms in between the two new membranes.

McGraw Hill - Mitosis and Cytokinesis Cytokinesis in Animal and Plant Cells (3 min)49The Stages of the Cell Cycle

Mitosis (6:10)50

a) metaphaseb) anaphasec) telophased) prophasee) interfase(f)f) anaphase(g)g) cytokinesisVideo clips and AnimationsMitosis (1:29)Eukaryotic Cell Cycle | Biology | Genetics (4:19)Stages of Mitosis (4:30)Mitosis (6:10)Cell Cycle and Mitosis (6:20)Meiosis (5:27)PBS (Mitosis vs Meiosis) Interactive

Section 11.4Meiosis55Important VocabularyMeiosisDiploidHaploidGameteSexual Reproduction

56Chromosome NumberChromosomes - strands of DNA and protein inside the cell nucleus - are the carriers of genes.

The genes are located in specific positions on chromosomes.

Meiosis (3:30)

57Homologous Chromosomes A body cell in an adult fruit fly has eight chromosomes, as shown in the figure.Four of the chromosomes come from its male parent, and four come from its female parent.These two sets of chromosomes are homologous, meaning that each of the four chromosomes from the male parent has a corresponding chromosome from the female parent.

Biology Meiosis (2:57)

58Diploid Cells A cell that contains both sets of homologous chromosomes is diploid, meaning two sets.The diploid number of chromosomes is sometimes represented by the symbol 2N.For the fruit fly, the diploid number is 8, which can be written as 2N = 8, where N represents twice the number of chromosomes in a sperm or egg cell.

59Haploid Cells Some cells contain only a single set of chromosomes, and therefore a single set of genes.

Such cells are haploid, meaning one set.

The gametes of sexually reproducing organisms are haploid.

For fruit fly gametes, the haploid number is 4, which can be written as N = 4.60ZygoteFertilized eggHaploid sperm + Haploid egg = diploid zygote

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Meiosis the Great Divide (7:40) Ameoba Sisters62Synapsis and TetradsDuring synapsis, the homologuous chromosomes pair up, forming a structure called a tetrad, which contains four chromatids.

63Crossing OverAs homologous chromosomes pair up and form tetrads, they undergo a process called crossing-over.First, the chromatids of the homologous chromosomes cross over one another.Then, the crossed sections of the chromatids are exchanged.Crossing-over is important because it produces new combinations of alleles in the cell.

64Independent AssortmentGenes for different traits can segregate independently during the formation of gametes.

Biology Meiosis (2:57)65Meiosis I

MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE IcentriolesSites of crossing overSpindle FibersSister chromatids remain attachedNuclearenvelopeChromatinSisterchromatidsTetradHomologouschromosomes separateMeiosis II

PROPHASE II METAPHASE II ANAPHASE II TELOPHASE IAND CYTOKINESISTELOPHASE IIAND CYTOKINESISCleavagefurrowHaploid daughter cellsformingSister chromatidsseparateMEIOSIS II: Sister chromatids separateAnimation of Meiosis (4 min)Phases of MeiosisMeiosis is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

Meiosis usually involves two distinct divisions, called meiosis I and meiosis II.

By the end of meiosis II, the diploid cell becomes four haploid cells.Meiosis Square Dance Discovery Education (3:21)68Meiosis I: InterphaseJust prior to meiosis I, the cell undergoes a round of chromosome replication called interphase I.

Each replicated chromosome consists of two identical chromatids joined at the center.

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Prophase I The cells begin to divide, and the chromosomes pair up, forming a structure called a tetrad, which contains four chromatids.As homologous chromosomes pair up and form tetrads, they undergo a process called crossing-over.70Metaphase IDuring metaphase I of meiosis, paired homologous chromosomes line up across the center of the cell.

71Anaphase IDuring anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell.When anaphase I is complete, the separated chromosomes cluster at opposite ends of the cell.

72Telophase IDuring telophase I, a nuclear membrane forms around each cluster of chromosomes.

73Cytokinesis Cytokinesis follows telophase I, forming two new cells.

Meiosis (1:49)

74Meiosis IMeiosis I results in two cells, called daughter cells.Because each pair of homologous chromosomes was separated, neither daughter cell has the two complete sets of chromosomes that it would have in a diploid cell.The two cells produced by meiosis I have sets of chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.

75Meiosis II The two cells produced by meiosis I now enter a second meiotic division.

NOTE: Unlike the first division, neither cell goes through a round of chromosome replication before entering meiosis II.

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Prophase IIAs the cells enter prophase II, their chromosomeseach consisting of two chromatidsbecome visible.

The chromosomes do not pair to form tetrads, because the homologous pairs were already separated during meiosis I.

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Metaphase IIDuring metaphase of meiosis II, chromosomes line up in the center of each cell.78

Anaphase IIAs the cell enters anaphase, the paired chromatids separate.79Telophase IIThe nuclear envelope reforms around the chromatids.In the example shown here, each of the four daughter cells produced in meiosis II receives two chromatids.

80Cytokinesis These four daughter cells now contain the haploid number (N)just two chromosomes each.

Meiosis Square Dance (Full Version is 5:11)This is repeated 2x in the videoMeiosis: Crossing Overand Variability81Meiosis I

MEIOSIS I: INTERPHASE PROPHASE I METAPHASE I ANAPHASE IcentriolesSites of crossing overSpindle FibersChromatids remain attachedNuclearenvelopeChromatinSisterchromatidsTetradHomologous chromosomes separateHomologous chromosomes line up in the middleMeiosis II

PROPHASE II METAPHASE II ANAPHASE II TELOPHASE IAND CYTOKINESISTELOPHASE IIAND CYTOKINESISMEIOSIS II: Sister chromatids separateCleavage furrowChromatids separate4 Haploid daughter cells formingChromosomes line up in the middleFormation of GametesSpermatogenesisOogenesisForms 4 haploid spermForms 1 ovum (egg) and 3 polar bodies

Oogenesis (3:53)84Spermatogenisis