BIO 118 1st Edition Lecture 11 Outline of Last Lecture I Steps of Cell Cell Signaling Outline of Current Lecture I Intro to Cell Division II Contrasting Mitosis and Meiosis III Functions of Cell Division IV What is a Chromosome V Chromosome Morphology Changes Before Mitosis VI Chromosome Replication VII The Cell Cycle VIII M Phase and Interphase IX Interphase S Phase X Interphase Gap Phases XI Mitosis Overview XII Chromosome Changes During Cell Cycle XIII Events in Mitosis XIV Prophase XV Prometaphase XVI Metaphase XVII Anaphase XVIII Telophase XIX Cytokinesis XX Cell Division XXI Different Cell Types Undergo Cell Division Differently Current Lecture Introduction to Cell Division Cells arise through the division of preexisting cells Two types of cell division Meiosis Mitosis Both are accompanied by cytokinesis o The cytoplasm of the cell divides into two distinct daughter cells Contrasting Mitosis and Meiosis Meiosis leads to These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Production of gametes eggs and sperm o Daughter cells have half the amount of genetic material as the parent cell Mitosis leads to o The production of all other cell types referred to as somatic cells o Genetic material is copied and then divided equally o Daughter cells are genetically identical to the parent cell Functions of Cell Division Mitosis Cytokinesis Cell division is responsible for 3 key events in multicellular eukaryotes o Growth o Wound Repair o Asexual Reproduction What is a Chromosome DNA encodes the cell s genetic information A gene is a section of DNA that encodes a specific RNA and therefore a specific protein Chromosomes contain a single long double helix of deoxyribonucleicacid DNA Are wrapped around proteins Chromosomes can be stained with dyes observed under the light microscope Chromosome Morphology Changes Before Mitosis The purpose of mitosis is to distribute chromosomes to daughter cells during cell division Each chromosome is replicated before mitosis Chromosomes condense from long thin filaments into compact structures that can be moved around the cell during mitosis At the end of mitosis one of the chromosome copies is distributed to each of two daughter cells Chromosome Replication Before mitosis each chromosome is replicated Each of the DNA copies in a replicated chromosome is called a chromatid Chromatids are joined together along their entire length Are also joined at a specialized region of the chromosome called the centromere Chromatids from the same chromosome are referred to as sister chromatids A replicated chromosome consists 2 chromatids Still considered a single chromosome Genetically they are identical The Cell Cycle Four phases in the cell cycle o M Phase o An Interphase consisting of G1 S G2 phases Gap phases allow the cell to grow large enough synthesize enough organelles to ensure the daughter cells are normal in size and function The cell cycle is the orderly sequence of events that occurs from the formation of a eukaryotic cell through the duplication of its chromosomes to the time it undergoes cell division A visualization technique called autoradiography allowed researchers to identify the part of the cell cycle during which DNA replication occurs M Phase and Interphase Growing cells cycle between two phases o A dividing phase called the mitotic phase o A non dividing phase called interphase Interphase S Phase Chromosome replication occurs only during interphase The stage in which DNA replication occurs is called the synthesis S phase 6 8 hours Interphase Gap Phases Interphase also includes two gap phases during which no DNA synthesis occurs G1 Phase o Is the first gap o Occurs before the S phase o The longest phase o 7 9 hours G2 Phase o The second gap o 4 5 hours o Occurs between S phase and mitosis o Organelles replicate o Additional cytoplasm is made in preparation for cell division It takes a cell about 24 hours to complete one cell cycle Mitosis Overview Mitosis results in the division of replicated chromosomes Formation of two daughter nuclei with identical chromosomes genes in each daughter Usually accompanied by cytokinesis Chromosomes Change During the Cell Cycle Eukaryotic chromosomes consist of DNA associated with histone proteins In eukaryotes this DNA protein material is called chromatin o Is relaxed or uncondensed forms long threadlike strands After replication during S phase each chromosome consists of 2 genetically identical sister chromatids attached at the centromere At the start of mitosis the replicated chromosomes condense Events in Mitosis During mitosis o The 2 sister chromatids separate to form independent chromosomes o One copy of each chromosome goes to each of the 2 daughter cells o Each daughter cell receives a copy of the genetic information that is contained in each chromosome o Mitosis is a continuous process with five subphases based on specific events Prophase Prometaphase Metaphase Anaphase Telophase Prophase During prophase chromosomes condense First become visible in the light microscope The mitotic spindle is made up of microtubules called spindle fibers Forms from a microtubule organizing center Polar microtubules push the poles of the cell away from each other during mitosis Kinetocore microtubules pull chromosomes to the poles of the cell during mitosis Prometaphase During prometaphase the nuclear envelope breaks down The nucleolus disappears Kinetochore microtubules from each mitotic spindle attach to one of the sister chromatids of each chromosome Attachment occurs in the centromere region at the kinetocore Metaphase During metaphase formation of the mitotic spindle is completed Motor proteins on the kinetochore microtubules pull each chromosome in opposite directions causing the chromosomes to line up in the middle of the cell The imaginary plane formed by metaphase is called the metaphase plate Anaphase During anaphase centromeres split Sister chromatids are pulled by the spindle fibers toward opposite poles of the cell Replicated chromosomes split into two identical sets of unreplicated chromosomes As soon as they are no longer attached at the centromere sister chromatids become daughter chromosomes Motor proteins of the polar microtubules push the two poles of the cell away from each other Telophase During telophase a new nuclear envelope begins to form around each set of chromosomes The mitotic spindle
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