Centrosomes and Centrioles • Centrosomes organize microtubules • Centrioles: bundles of microtubules – Pull chromosomes, form core in cilia Cilia and Flagella • Motor proteins • 2:9 microtubule pattern • Cilia move fluids • Flagella move sperm cell Membranous Organelles: Create cell compartments • Internal lumen and membranes for protected reactions • Mitochondria: Generates cell energy (ATP) , have DNA Endoplasmic Reticulum (ER) & Ribosomes • Smooth ER: Lipid synthesis & conversion • Rough ER: Ribosomes, protein assembly & transport vesicles Cell Growth and Reproduction • Cell Cycle- the series of changes • Two Phases – Interphase: Cell grows and carries on its usual activities – Cell division or mitotic phase: cell divides into two daughter cells Cell Life Cycle: Interphase or Growth Phase (G1, S, G2) - “betweenphases”, prepares for mitosis by duplicating DNA and organelles S phase: DNA replication. New histones are made and assembled into chromatin G1 : The cell is metabolically active, synthesizing proteins and growing G2 Very brief. Enzymes and other proteins synthesized. By the end, centriole replication is completed Mitosis: Reproduction of DNA • nuclear division for all somatic or body cells • diploid cells (2N) result in making 2 diploid daughter cells (2N). • Four stages – – – – Prophase Metaphase Anaphase Telophase Prophase = puddle of DNA • “before-phase” • chromatin shorten into chromosomes • centrioles move to opposite ends, spindle fibers form • nuclear envelope and nucleolus disappear Metaphase: Middle • “middle-phase” • chromosomes line up on equatorial plate • centromeres attach to fibers Anaphase: Apart • “apart phase” • chromosomes split and chromatid is pulled to opposite centrioles • spindle fibers shorten Telophase: Tearing • “end phase” • chromosomes elongate to chromatin • nuclear envelope and nucleolus reappear • Cytokinesis: allows cell membrane to pinch in to separate 2 new daughter cells – Separate from Telophase Cell Division • Mitosis: division of the nucleus • Cytokinesis: division of the cytoplasm • The amount of nutrients a growing cell requires is directly related to its volume Regulators of Cell Division 1. Chemical signals ( growth factors, hormones) released by other cells 2. Availability of space: Normal cells stop proliferating when they begin touching ( contact inhibition) 3. Cyclins and Cdks: proteins that allow the cell to enter S phase Meiosis: Reproduction of Sex Cells A. Provides genetic variation in offspring because daughter cells are haploid (1N), where parent cells were diploid (2N). B. Chromosomes exist in pairs called homologous pairs; one from each parent. 1. Two kinds of chromosomes: 1. *autosomes- #s 1-22; determine body characteristics 2. *sex chromosomes- #23; determine if male (XY) or female (XX) 2. Somatic cells contain the diploid number of chromosomes, 2N = 46 for humans. 3. Gametes contain the haploid number of chromosomes, which is ½ the diploid number, 1N = 23 for humans. Meiosis I – reduction of chromosomes 4 phases1. Prophase I- homologous chromosomes pair up, called tetrads; crossing-over? 2. Metaphase I- homologous pairs line up on equatorial plate 3. Anaphase I- homologous pairs split, each chromosome moves to opposite centrioles 4. Telophase I – cytokinesis occurs to separate into 2 daughter cells Meiosis II • division of chromosomes, similar to mitosis except the 4 phases are II. Result 4 haploids cells (1N). In male, generate 4 sperm. In female, generate 1 large egg Diploid Cells (2N) Meiosis Haploid Cells (1N) Fertilization of 1N Egg + 1N Sperm = 2N Zygote Three sources of genetic variability: 1. Independent assortment of homologuescombination of maternal and paternal chromosomes in gametes is 2 23 or 8 million. 2. Crossing over- genes on other chromosomes can stick 3. Random fertilization – which sperm wins?