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 3/5/2016Template copyright

Limits 1. DNA Overload Cells do not make extra copies of DNA as they grow. This can cause an “information crisis”. –Library –Internet Access Cannot “wait” for functions to occur. 3/5/2016Template copyright

Limits to Cell Growth 2. Exchanging Materials The rate at which food, water, oxygen, and waste can enter/exit a cell. Depends on surface area. –Cells want a larger surface area compared to its volume. 3/5/2016Template copyright

3/5/2016Template copyright : Cell Growth Growth from more and more cells The volume increases faster than the surface area.

Ratio of Surface Area to Volume Cells shaped like cubes 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? 3/5/2016Template 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. Large cells would have difficulty transporting food and nutrients into and out of the cell. 3/5/2016Template copyright

3/5/2016Template copyright Cell Division Cells divide to produce new cells. What must be copied before a cell divides? “Genetic Library”

3/5/2016Template 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

3/5/2016Template copyright Chromosomes Structures that carry the genetic information What are chromosomes made of? Circular in proks X-shaped in euks

Sister Chromatids A chromosome consists of 2 identical sister chromatids. Attached by a centromere. As a cell divides, one chromatid goes to each new daughter cell. 3/5/2016Template copyright

3/5/2016Template 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

The Cell Cycle Draw and label the Cell Cycle in your Notebooks. Describe each event that takes place. 3/5/2016Template copyright

3/5/2016Template 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

3/5/2016Template copyright Interphase phases that occur in between cell divisions –G 1 phase: growth occurs, organelles and proteins being synthesized –S phase: synthesis, chromosomes duplicate themselves –G 2 phase: Cell prepares for mitosis

Mitosis – The M Phase Prophase Metaphase Anaphase Telophase 3/5/2016Template copyright

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3/5/2016Template copyright Prophase longest phase Chromatin condenses chromosomes appear Centrioles separate Spindle forms Nuclear envelope breaks down

3/5/2016Template copyright Metaphase shortest phase chromosomes line up across center of cell chromosomes attach to spindle

3/5/2016Template copyright Anaphase centromeres split Sister chromatids separate chromosomes move toward opposite sides

3/5/2016Template copyright Telophase spindle breaks form two nuclei around each set of chromosomes Cytokinesis –Cytoplasm divides –in animal cells, the cell membrane is pinched –in plants, a cell plate forms midway between the divided nuclei

10-3 Regulating the Cell Cycle Controls on cell growth and cell division can be turned on or off. Injury occurs –Cells divide rapidly. –As healing completed, division slows down and returns to normal. CYCLIN: proteins that regulate the timing of the cell cycle in eukaryotic cells. What would happen when repair an injury if cycle was not controlled? 3/5/2016Template copyright

Cell Cycle Regulators Internal: Proteins respond to events inside the cell. Only allow cell cycle to proceed after chromosomes have been copied. External: Proteins that respond to events outside the cell. Growth Factors Molecules/Signals found on other cells 3/5/2016Template copyright

3/5/2016Template copyright Uncontrolled Cell Growth cancer: a disorder in which some cells have lost the ability to control their own rate of growth continue to grow and divide until the supply of nutrients is exhausted

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 have the ability to spread to other sites in the body or to invade and destroy tissues Benign versus Malignant 3/5/2016Template 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 Body cell has 8 chromosomes –4 from female4 from male –Homologous chromosomes –Diploid number = 8 or 2N (two sets) –N = 4 –Haploid number = 4 or N (one set) 3/5/2016Template copyright

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

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 diversity 3/5/2016Template 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 has prophase II, metaphase II, anaphase II, and telophase II end up with four cells with half the amount of chromosomes as the original

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 3/5/2016Template 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? 3/5/2016Template copyright