Chapter 10: Cell Growth and Division

Limits to Cell Growth Why do cells need to remain small? Cells divide rather than grow larger for two main reasons –1. More demands on a cell’s DNA –2. Movement of nutrients and wastes 2/11/2016Template copyright

Limits to Cell Growth 1. DNA Overload Cells do not make extra copies of DNA as they grow. This can cause an “information crisis”. –Library –Internet Access Cells cannot “wait” for DNA and other contents to perform their functions. 2/11/2016Template copyright

Limits to Cell Growth 2. Exchanging Materials The rate at which food, water, oxygen, and waste can enter/exit the cell’s membrane depends on surface area. 2/11/2016Template copyright

2/11/2016Template copyright : Cell Growth As a cell gets larger, the volume increases faster than the surface area Why is this a problem for cells? Do cells want a larger surface area or volume?

Ratio of Surface Area to Volume For cuboidal cells, Surface area = L x W x # of sides Volume of cell = L x W x H What is SA and V of cell that has a length of 1 cm? What is the ratio of SA to V? 2/11/2016Template copyright

Surface Area to Volume Ratio If length of the cell tripled to 3 cm, The SA = 3 x 3 x 6 = 54 The V = 3 x 3 x 3 = 27 The ratio = 54/27 = 2:1 or 2 V increases more rapidly than SA Ratio of SA to V decreases. This is a major problem in a cell. Consider Pequannock Township and the Boulevard. Larger cells would have difficulty transporting food and nutrients into and out of the cell. 2/11/2016Template copyright

2/11/2016Template copyright Cell Division Process in which the parent cell divides into two daughter cells Each new daughter cell has an exact copy of genetic information Compare them.

2/11/2016Template copyright Cell Division: Mitosis and Cytokinesis first stage mitosis: the process in which nucleus of the cell is divided into two nuclei –Daughter cells identical to parent cell second stage cytokinesis: process by which the cytoplasm divides, thus forming two distinct cells

2/11/2016Template copyright Chromosomes What do they do? Contain genetic information What are they made of? Made of DNA and protein Where is DNA found in a prokaryotes and eukaryotes? Proks – Cytoplasm Euks - Nucleus

Sister Chromatids A chromosome consists of 2 identical sister chromatids. Attached by a centromere. 2/11/2016Template copyright

2/11/2016Template copyright Chromatin composed of DNA and protein Histones help fold DNA so it can fit in the nucleus nucleosomes: tiny particles formed from the DNA and histone molecules

2/11/2016Template copyright The Cell Cycle Period of time from one cell division to the next division. –Divide at different times. Human adult cells is 20 hours Need controls for division and growth

2/11/2016Template copyright Interphase phases that occur in between cell divisions –G 1 phase: growth occurs, organelles copy themselves –S phase: synthesis, chromosomes duplicate themselves –G 2 phase: Cell prepares for mitosis

Mitosis – The M Phase Prophase Metaphase Anaphase Telophase and Cytokinesis 2/11/2016Template copyright

2/11/2016Template copyright Prophase longest phase Chromatin condenses chromosomes appear Centrioles separate Spindle forms Nuclear envelope breaks down

2/11/2016Template copyright Metaphase shortest phase chromosomes line up across center of cell chromosomes attach to spindle

2/11/2016Template copyright Anaphase centromeres split Sister chromatids separate chromosomes move toward opposite sides

2/11/2016Template copyright Telophase spindle breaks form two nuclei around each set of chromosomes

Cytokinesis –Animals cell membrane pinched Cleavage Furrow –Plants –cell plate forms midway between the divided nuclei Cell Plate 2/11/2016Template copyright

10-3 Regulating the Cell Cycle Controls on cell growth and cell division can be turned on or off. –Similar to a light switch Cells will divide rapidly to repair tissues. –Cell division returns to normal as healing process is completed. CYCLIN: proteins that regulate the timing of the cell cycle in eukaryotic cells. 2/11/2016Template copyright

Cell Cycle Regulators Internal: Proteins respond to events inside the cell. Only allow cell cycle to proceed after chromosomes have been copied. P53 Gene External: Proteins that respond to events outside the cell. Growth Factors Molecules/Signals found on other cells 2/11/2016Template copyright

2/11/2016Template copyright Uncontrolled Cell Growth cancer: A cell that has lost its ability to control its rate of growth and division Grow and divide until nutrients are used up

Cancer Cells Tumor – Mass of growing tissue Metastasize - To spread from one part of the body to another causing secondary tumors to form. Malignancy - cancerous cells that spread to other sites in the body –Invade and destroy other tissues Benign versus Malignant 2/11/2016Template copyright

11-4 Meiosis chromosome number –each organism has two sets of chromosomes –one set comes from each parent –homologous chromosomes: corresponding chromosomes from each set –diploid: cell with two sets of homologous chromosomes –haploid: cell with one set of chromosomes

Chromosome Numbers Drosophilia fruit fly A gamete contains 4 chromosomes What is a gamete? What is N? How many chromosomes in a haploid cell? How many chromosomes in a somatic cell? 2/11/2016Template copyright

The Phases of Meiosis meiosis: reduction division in which the number of chromosomes per cell is cut in half homologous chromosomes in a diploid cell are separated creates gamete cells What are gametes?

Meiosis Animation 385R0whttps:// 385R0w 2/11/2016Template copyright

Meiosis I Prophase I Tetrad – 4 chromatids joined together –2 pairs of homologous chromosomes joined together Crossing-over – pairs of homologous chromosomes exchange sections of DNA Exchange provides genetic variation 2/11/2016Template copyright

Meiosis I prophase I: homologous chromosomes seek out one another to form a tetrad metaphase I: homologous chromosomes line up across center of the cell –crossing over occurs: exchange portions of their chromatids anaphase I: homologous chromosomes separate telophase I: two new cells are formed

Meiosis II happens exactly like mitosis prophase II, metaphase II, anaphase II, and telophase II Four cells - half the amount of chromosomes (N) as the parent cell

Gamete Formation Gametes are the reproductive cells of an organism that reproduces through sexual reproduction. Males  Sperm Cell (N) Females  Egg Cell (N) –Only 1 out of the 4 haploid cells produced receives cytoplasm –The other 3 cells are called Polar Bodies –Not involved in reproduction 2/11/2016Template copyright

Pages 276 and 277 Draw the phases of Meiosis I and Meiosis II. Label the phases to understand what is taking place. 2/11/2016Template copyright

Comparing Mitosis and Meiosis Mitosis produces 2 genetically identical daughter cells (Diploid). –One 2N cell  Two 2N cells Meiosis produces 4 genetically different gamete cells (Haploid). –One 2N cell  4 N cells How does a fertilized egg have 2N chromosomes? 2/11/2016Template copyright

DO NOW ANSWERED Meiosis I –2 sets of homologous chromosomes pair –Tetrad is formed –Crossing over occurs –Produces new combinations of alleles –Homologous chromosomes pulled to opposite ends of the cell –Two new haploid daughter cells form Meiosis II 2/11/2016Template copyright

Meiosis II –Chromosomes line up in Metaphase II –Chromatids separate and one moves to each new cell in Anaphase II –4 new genetically different daughter cells are formed –Different from each other and the original cell Produces more Genetic Diversity 2/11/2016Template copyright