Chapter 6: Cell Division PDF

Chapter 6: Cell Division Prof. Calkins SCB 101 Topics in Biology The Cell Cycle The cell cycle: a sequence of events that makes up the life of a typical eukaryotic cell From the moment of its origin to the time it divides to produce two daughter cells Cells divide for two reasons: 1...

Chapter 6: Cell Division Prof. Calkins SCB 101 Topics in Biology The Cell Cycle The cell cycle: a sequence of events that makes up the life of a typical eukaryotic cell From the moment of its origin to the time it divides to produce two daughter cells Cells divide for two reasons: 1. To reproduce the organism 2. To grow and repair cells of a multicellular organism The Cell Cycle Two main stages in the cell cycle of eukaryotes: 1. Interphase 90% of a cell’s life When the cell does what it normally does Preparing for cell division 2. Cell division (Mitosis) The last stage in a cell’s life cycle When the DNA is duplicated and divided into daughter cells One cell becomes two cells Interphase G1 phase (gap 1) - First phase in a newly divided cell - Takes in nutrients, produce proteins - Cell grows and prepares for DNA replication S phase (synthesis) - DNA is replicated. - At the end of the S phase, the cell now has twice as much DNA as normal. G2 phase (gap 2) - After S phase but before cell division - Gets ready for cell division - Are raw materials available for the cell to divide? Checkpoints in the Cell Cycle Cell cycle regulatory proteins enable the cell to pass through critical cell cycle checkpoints. Cell cycle checkpoints: G1 checkpoint Stops cell cycle if the cell is too small, the nutrient supply is inadequate, or the cell’s DNA is damaged G2 checkpoint Stops cell cycle if the cell is too small, the nutrient supply is inadequate, the cell’s DNA is damaged, or when chromosome duplication in the S phase is incomplete  Tumor: cell mass created by rapid, runaway cell division Good Cells This usually happens when cells ignore the cell cycle Gone checkpoints Bad Tumor cells are benign when cells remain confined to one site.  Tumor cells are malignant, or cancerous when: Cells become anchorage independent. Most cells are firmly anchored in Good one place and will stop dividing if they are detached from their surroundings. Cells Cells break away and invade other tissues and form metastases. Gone Bad The spread of cancer from one organ to another Cells promote angiogenesis The formation of new blood vessels Recap Q1: What could happen if the cell’s checkpoints are disabled? The cells could become defective, deformed or even cancerous Q2: What is the advantage of stopping the cell cycle if the cell’s DNA is damaged? DNA tells our cells how to behave, so if that is damaged, then the cell cycle should stop so the wrong messages don’t get sent (and cells don’t become cancerous)  What is DNA? Where is it located in the cell? Our genetic blueprint. It has all of the information for our cells to function properly, and is located within the nucleus of eukaryotic cells Recap What do you think DNA must do before a cell can divide? Duplicate itself, because both daughter cells need that information to function Cell Division Cell division The last stage in a cell’s life cycle When the DNA is duplicated and divided into daughter cells One cell becomes two cells Cell Division in Prokaryotes Binary fission in prokaryotes is asexual reproduction. Occurs in prokaryotes and some single-cell protist eukaryotes 1- The cell copies their chromosome 2- Chromosomes move into separate ends of the cell 3- The cell splits into two daughter cells, which receive one chromosome each Daughter cells are genetically identical clones.  Cell division of somatic cells, or body cells Asexual Mitosis Produces two identical daughter cells Breakout Rooms Group 1: Interphase (S-Phase specifically) Group 2: Prophase Group 3: Metaphase Group 4: Anaphase Group 5: Telophase & Cytokinesis DNA Synthesis Interphase ‘S’ phase DNA needs to replicate itself before cell division This replication happens during interphase DNA copies itself so that the cell has TWO identical copies of each chromosome, called sister chromatids They are held together by a centromere to keep them organized before division Mitosis Prophase Chromosomes condense Nuclear membrane dissolves Spindle forms Mitosis Metaphase Chromosomes line up in the center Anaphase Spindle fibers pull chromatids apart Chromatids migrate to separate poles Telophase/Cytokinesis Nuclear membrane reforms Cell pinches in two Recap What is the correct sequence of steps in mitosis? a. Interphase, prophase, metaphase, anaphase, telophase, cytokinesis b. Prophase, anaphase, metaphase, telophase, interphase, cytokinesis c. Cytokinesis, telophase, anaphase, metaphase, prophase, interphase d. Anaphase, metaphase, telophase, prophase, interphase, cytokinesis Meiosis Meiosis: cell division used in sexual reproduction to produce sperm and egg cells Gametes: sex cells Gametes are haploid, or only contain one copy of each chromosome In contrast, somatic cells possess diploid cells that are identical to one another. Diploid cells contain two copies of each chromosome Same DNA as the parent cells Produced by MITOSIS, never meiosis How Do Eggs and Sperm Form? Sexually reproducing organisms make gametes (sex cells) Eggs and sperm are produced by meiosis Sperm are formed in the testes Eggs are formed in the ovaries Human Chromosomes 46 chromosomes organized into 23 homologous pairs (one from mom, one from dad) Begins with a single diploid cell (two sets of chromosomes) Meiosis halves the number of chromosomes, ending in a haploid cell Ends with four haploid cells (one set of chromosomes) Meiosis Overview Meiosis I: The First Round of Cell Division Interphase Growth Chromosomes replicate Prophase I Chromosomes condense Nuclear membrane dissolves Spindle forms Metaphase I Homologues line up in the center Meiosis I Anaphase I Homologues separate to opposite poles Telophase I Nuclear membranes form Cytokinesis Cell pinches in two Each daughter cell is haploid Meiosis II: The Second Round of Cell Division Prophase II Chromosomes attach to the spindle Metaphase II Chromosomes line up in the center Anaphase II Chromosomes separate Meiosis II Telophase II Nuclear membrane reforms Cytokinesis II Cells pinch in two End result of meiosis is four haploid daughter cells. Recap: What is produced by the process of meiosis? a. Duplicate cells b. Diploid gametes c. Haploid gametes d. A zygote Recap: What is the major difference between mitosis and meiosis? a. In meiosis, a cell is completely replicated into two identical daughter cells. In mitosis, four daughter cells are haploid, not replicates of the original cell. b. In mitosis, a cell is completely replicated into two identical daughter cells. In meiosis, four daughter cells are haploid, not replicates of the original cell. c. Meiosis happens in embryos and mitosis happens in adult human cells. d. Meiosis is part of the process of embryogenesis and Recap Why is it important that gametes be haploid (only have one copy of each chromosome)? a. Because they need to have extra chromosomes to develop into a complete organism. b. Because the sperm and egg cells need to be very small. c. It isn’t really important. That’s just how it works. d. Because if they weren’t, when they joined at fertilization the resulting zygote would have twice the Fertilization Fertilization: the fusion of two haploid gametes, resulting in a zygote Zygote: a single diploid cell Contains all the DNA Undergoes mitosis to form the new complete organism Recap Q1: Is a zygote haploid or diploid? Diploid because it combines chromosomes from BOTH parents Q2: Which cellular process creates a baby from a zygote? Mitosis: everyday cells are now being replicated to form a fetus Homework: Lab 2: Microscope Due midnight before next class