Cell Division Bio 105: Cell Division Starts with DNA Replication Laboratory 8 DNA Replication When does DNA replicate? Just prior to cell division Multicellular Organisms Grow Replace old cells Unicellular Organisms Reproduce Chromosomes DNA Replication DNA wound up in coils and folded Replicated DNA Duplicated state 2 strands Chromatids or sister chromatids Held together by a centromere 1
DNA Replication After replication Each chromosome will be made of 2 sister chromatids Remember chromosomes come in pairs 2 chromosomes, each with 2 chromatids Remember DNA is in the nucleus 2
Cell Cycle: Stages of Cell Division 2 main phases Interphase Prepares for cell division DNA replication Mitotic phase Chromosomes separate Cell Divides Cell Cycle: Stages of Cell Division Average animal cell cycle about 24 hours Mitosis About 30 minutes Most of the time spend in G1 Cells grows in size About 12 hours Interphase End of Interphase: DNA has replicated Cell grows Makes new cellular components DNA is replicated ** Check points Mitosis 4 Phases Prophase Metaphase Anaphase Telophase Think about how hard it would be to divide the DNA into two equal parts if it was in the uncondensed form 3
Mitosis: Prophase Chromosomes condense Nuclear membrane breaks down Two centrioles (one centrosome) begin to move to opposite ends of the cell Microtubules form Microtubules Mitosis: Prophase Mitosis: Metaphase Microtubules (mitotic spindles) attach to the chromosomes Microtubules line up the chromosomes at the center of the cell (the equator) Mitosis: Metaphase 4
Mitosis: Anaphase Sister chromatids are pulled apart by the microtubules Chromatids move towards the poles. Chromatids Chromosomes Mitosis: Anaphase Chromosomes begin to uncondense Nuclear membrane forms Cell begins to divide in half Mitosis: Telophase Mitosis: Telophase Cell divides completely forming two separate cells Cytokinesis Cytokinesis 5
Cell Division - Mitosis Mitosis Overview https://www.youtube.com/watch?v=c6hn3 sa0ip0 Review Questions Where does DNA replication take place? When does DNA replication take place? During what stage does the nuclear membrane breakdown? During what stage do the chromosomes line up at the equator? During what stage do the chromosomes being to uncondense? Review Questions At the end of mitosis, how many cells are there? At the end of mitosis, how many chromosomes are there in each cell? At the end of mitosis, are the chromosomes in the duplicated state? 6
Mitosis Cell Types Occurs in all the body s cells except for gametes Somatic cells Gametes Cells responsible for reproduction Gametes Cell Division Sperm Eggs Cell division = Meiosis Halving their number of chromosomes Terminology Diploid Cells that have 46 chromosomes or 23 pairs All somatic cells are diploid (2n) Haploid Cells that have 23 chromosomes All gametes are haploid (1n) Meiosis Diploid cell divides to produce haploid reproductive cells Meiosis Meiosis Interphase Chromosomes (DNA) duplicated Then there are 2 cell divisions Pairs of chromosomes Each chromosome has 2 chromatids after DNA replication Interphase Chromosomes duplicate 1 st division Chromosome pairs separate and cell divides 2 nd division Chromatids separate and cell divides 7
DNA replicates Meiosis Chromosomes become duplicated Cell is diploid (2n) Homologous chromosomes separate and cell divides The chromatids separate and cell divides 4 haploid cells (1n) Meiosis Forms gametes Start as diploid cells and end up haploid cells 2 stages Meiosis I Meiosis II Each stage has Prophase, Metaphase, Anaphase and Telophase Meiosis Crossing Over End of Interphase DNA is replicated Prophase I Duplicated chromosomes condense and intertwine Produces genetic variation = crossing over Genetic material is exchanged between the homologous chromosomes Meiosis: Prophase I Duplicated chromosomes condense and crossover Nuclear membrane breaks down 2 Centrioles (centrosomes) begin to move to opposite ends of cell Microtubules form Meiosis: Metaphase I Microtubules (mitotic spindles) attach to the chromosomes Microtubules line up the chromosomes at the center of the cell (the equator) Chromosomes arrange themselves randomly Independent assortment 8
Meiosis: Anaphase I Chromosomes in the pairs are separated Different than mitosis Here the chromosomes in a pair are separated from each other Now 23 chromosomes are on each side Meiosis: Telophase I Nuclear membrane forms Cell divides in half Have 2 haploid cells (1n) 23 chromosomes total Chromosomes are in duplicated form Cell now enters Meiosis II Meiosis II Meiosis II Prophase II 23 chromosomes are already condensed Nuclear membrane dissolves Metaphase II Chromosomes line up at the equator Anaphase II Chromatids separate Telophase II Cells separate Result: 4 haploid cells, each has 23 chromosomes NOT in the duplicated state Meiosis https://www.youtube.com/watch?v=- DLGfd-Wpr4 9
Review Questions At the end of Meiosis I, how many cells are there? At the end of Meiosis I, are these haploid or diploid cells? At the end of Meiosis I, how many chromosomes are there in each cell? At the end of Meiosis I, are the chromosomes in the duplicated state? Review Questions At the end of Meiosis II, how many cells are there? At the end of Meiosis II, are these cells haploid or diploid? At the end of Meiosis II, how many chromosomes are there in each cell? At the end of Meiosis II, are the chromosomes in the duplicated state? Genetic Diversity 2 places in meiosis that contribute to genetic diversity Prophase I Crossing over Metaphase I Independent Assortment Gametes Meiosis and Gender Contain 23 chromosomes Not in duplicated form One of these chromosomes will be a sex chromosome Eggs = X chromosome Sperm = either X or Y chromosome 10
Spermatogenesis Sperm produced in male testes One cell 4 sperm Each sperm: 23 chromosomes, not in duplicated form X or Y chromosome Small head and long tail Flagellum for locomotion Spermatogenesis Contain the genetic material to deliver to the egg Head contain the chromosomes and lots of mitochondria About 400 million sperm are produced each day 11
Oogenesis Egg Formation Ovaries produce eggs One cell one egg and 3 non-functioning polar bodies One egg gets most of the cytoplasm Other 3 not able to survive 23 chromosomes, not in duplicated form X chromosome One egg is large enough to support the embryo Oogenesis All of the cells that produce the eggs are made before the female mother is even born Each month one of these cells will leave the ovary and go on to mature Produce the egg and polar bodies Review Mitosis and Meiosis both start with a diploid cell (46 chromosomes, 23 pairs) Before both the DNA replicates forming duplicated chromosomes, each containing two chromatids Mitosis somatic cells Cells other than gametes Meiosis produces gametes Mitosis Review The chromatids are separated to produce 2 cells Each with 46 chromosomes 23 pairs of non-duplicated chromosomes Cells are diploid (2n) No exchanging of genetic material Review Meiosis I Pairs of chromosomes line up and the chromosomes are separated Results in 2 cells, each with 23 chromosomes in the duplicated state Meiosis II Chromatids separated Results in 2 haploid cells that contain 23 nonduplicated chromosomes One original cell 4 haploid cells 12
17-17 Important Concepts Know the 2 phases of the cell cycle Interphase and Mitosis Know what happens in each phase Mitosis Know each stage, the order of the stages and what happens in each stage Be able to recognize each stage of mitosis from pictures, models and microscope slides Why are check points important in interphase? Important Concepts Know what state the cell and the chromosomes are in at the beginning and end of Mitosis Meiosis I Meiosis II Example: Are the cells haploid or diploid? Are the chromosomes duplicated or not? How many chromosomes are there in the cell? Are they in pairs? Important Concepts Know which cells undergo mitosis vs meiosis How is genetic diversity introduced into meiosis What are the events that add to diversity? When does each event occur? Important Concepts How is the gender of the offspring determined? How many functioning sperm are produced from one spermatocyte? What sex chromosomes can a sperm have? How many functioning eggs are produced from one oocyte? What sex chromosomes do eggs have? 13
Definitions The End Gametes Somatic cells Diploid Haploid Crossing over Independent assortment Cytokinesis Centromere Centrioles Centrosome Chromatid Polar bodies Spermatogenesis Oogenesis 14