3 I. Limits to Cell Growth Not enough DNA As a cell increases in size it doesn’t make more DNAIf a cell grows too large, new organelles can’t get the instructions they need to function
4 Exchanging Materials: a cell must move nutrients and wastes across the cell membrane Materials go in and out depending on surface areaFood & oxygen is used up depending on volumeRatio of Surface Area to Volumeto make it easier, think of the cell as a cubeSurface area = length x width x # of sidesEx: 1cm x 1cm x 6 sides =Volume = length x width x heightEx: 1cm x 1cm x 1cm =Double the cell length, what happens?24/8 or ratio of 3:1Triple the cell length, what happens?54/27 or ratio of 2:1As a cell gets larger, volume increases much more rapidly than surface area.If a cell becomes too big, it cannot exchange materials across the membrane fast enough.
5 Cell Size Surface Area (length x width x 6) Volume (length x width x height)Ratio of Surface Area to Volume
6 II. Cell Division Draw Chromosomes Carries the genetic information from one generation to the nextMade up of DNA and proteinsReplicated prior to cell division forming two identical “sister” chromatidsChromatids are attached by the centromereDrawsister
7 Cell Cyclecell cycle = series of events a cell goes through as it grows and dividesA cell grows, prepares for division, and divides to form two daughter cells, each of which begins the cycle againOrganized into phases:M phase – cell divisionmitosis – nucleus divisioncytokinesis – cytoplasm divisionInterphaseG1 phase – cell growth, makes new organellesS phase – DNA replicationG2 phase – preparation for mitosis, more growth, makes more enzymesa cell spends ~90% of its time in interphase
10 Mitosis Prophase Metaphase chromatin condenses centrioles separate spindle forms (microtubules that help separate chromosomes)Nucleolus disappears, nuclear membrane breaks downMetaphasechromosomes line up across the center of the cell on spindle
11 Anaphasesister chromatids separate at centromeres and move apartTelophasechromosomes gather at opposite ends, new nuclear envelopes form
12 CytokinesisTo complete the M phase, we must have cytokinesis = division of the cytoplasm of the cellAnimal cells - cell membrane is drawn inward until the cytoplasm is pinched into 2 new cellsPlant cells - cell plate forms midway between the divided nuclei; the cell plate gradually develops into a separating membrane
15 Review of Cell Reproduction Mitosis & Cytokinesis Review Link:
16 Check out Cells Alive! and Biology in Motion from class website for mitosis review.
17 III. Sex Cell Formation - Meiosis Chromosome NumberHumans have 23 pairs of chromosomes, fruit flies have 4 pairsHomologous = chromosomes that each have a corresponding chromosome from the opposite-sex parentDiploid (2N) = two sets of chromosomesHaploid (N) = one set of chromosomesFruit fly chromosomesHuman chromosomes
18 Meiosis I (reducing # of chromosomes) Phases of MeiosisMeiosis = process of forming sex cells, “reduction and division”Meiosis I (reducing # of chromosomes)Begin with diploid cells (2N)Chromosomes have already been replicatedEach chromosome pairs up with its homologous chromosome to form a tetrad (contains 4 chromatids)In prophase I in a tetrad, chromatids cross over one another, exchanging genetic info. (crossing-over)DRAW Fig , pg. 276Homologous chromosomes are pulled to opposite sides of the cell, new haploid daughter cells are formed (N)Homologouschromosomes
20 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.The chromosomes line up in a similar way to the metaphase stage of mitosis.The sister chromatids separate and move toward opposite ends of the cell.Telophase IIMeiosis II results in four haploid (N) daughter cells.
21 Body cell in a reproductive organ father’s chromosomemother’s chromosomechromosomes copiedcrossing-over4 unique gametes
22 Meiosis II (division of chromosomes at centromere) Meiosis II looks like mitosis except that crossing-over already occurredChromosomes line up during metaphaseSister chromatids separate during anaphaseAt the end, you have 4 cells that are genetically different (ex: 4 unique sperm cells)
23 C. Gamete Formation DRAW Fig. 11-17, pg. 278 Gamete = sex cell ***Use color to show crossing-over!C. Gamete FormationGamete = sex cellMales produce spermhaploideach sperm cell can be involved in reproductionFemales produce eggscell divisions are unevenonly one cell receives most of the cytoplasmother cells are called polar bodies
24 IV. Regulating the Cell Controls on Cell Division When cells come into contact with other cells they respond by not growingControls on cell growth and cell division can be turned on and offWith an injury, cells at edge of injury are stimulated to divide rapidly to begin healing
25 Cell Cycle RegulatorsRegulators = respond to events to speed up or slow down cell cycleCyclins = proteins that control the timing of the cell cycle in eukaryotic cellsA sample of cytoplasm is removed from a cell in mitosis.The sample is injected into a second cell in G2 of interphase.As a result, the second cell enters mitosis.
26 Growth factors – stimulate growth & division important in embryonic cells and wound healing Uncontrolled Cell GrowthCancer = a disease of the cell cycleCancer cells do not respond to signals that regulate growth of most cellsTumors = masses of cells that damage the surrounding tissueWhen a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the bodyKnown causes – smoking, tobacco, radiation exposure, viral infectionCancer cells do not respond to density dependent inhibition. Do not respond to restriction point, but sometimes stop dividing in the middle of any phase. Since 1951 cells from Henrietta Lacks (HeLa) have been dividing even without nutrients are said to be immortal. By contrast, most normal mammalian cells divide in culture about times before they stop dividing, age, and die off. Metastasizing occurs when the cancer cell surface is abnormal causing it to detach from the cellular matrix and spread to other tissues.