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BU BIOL 118 - Mitosis
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BIO 118 1st Edition Lecture 11Outline of Last Lecture I. Steps of Cell-Cell SignalingOutline of Current Lecture I. Intro to Cell DivisionII. Contrasting Mitosis and MeiosisIII. Functions of Cell DivisionIV. What is a Chromosome?V. Chromosome Morphology Changes Before MitosisVI. Chromosome ReplicationVII. The Cell CycleVIII. M Phase and InterphaseIX. Interphase: S PhaseX. Interphase: Gap PhasesXI. Mitosis OverviewXII. Chromosome Changes During Cell CycleXIII. Events in MitosisXIV. ProphaseXV. PrometaphaseXVI. MetaphaseXVII. AnaphaseXVIII. TelophaseXIX. CytokinesisXX. Cell DivisionXXI. Different Cell Types Undergo Cell Division DifferentlyCurrent LectureIntroduction to Cell Division- Cells arise through the division of preexisting cells- Two types of cell division: Meiosis &Mitosis- Both are accompanied by cytokinesiso The cytoplasm of the cell divides into two distinct daughter cellsContrasting 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 equallyo Daughter cells are genetically identical to the parent cellFunctions of Cell Division (Mitosis & Cytokinesis)- Cell division is responsible for 3 key events in multicellular eukaryotes:o Growtho Wound Repairo Asexual ReproductionWhat 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 microscopeChromosome 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 cellsChromosome 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 identicalThe Cell Cycle- Four phases in the cell cycle:o M Phaseo 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 partof the cell cycle during which DNA replication occursM Phase and Interphase- Growing cells cycle between two phases:o A dividing phase called the mitotic phaseo A non-dividing phase called interphaseInterphase: S Phase- Chromosome replication occurs only during interphase - The stage in which DNA replication occurs is called the synthesis (S) phase- 6-8 hoursInterphase: Gap Phases- Interphase also includes two gap phases, during which no DNA synthesis occurs- G1 Phaseo Is the first gapo Occurs before the S phaseo The longest phase o 7-9 hours- G2 Phaseo The second gapo 4-5 hourso Occurs between S phase and mitosiso Organelles replicate o Additional cytoplasm is made in preparation for cell division- It takes a cell about 24 hours to complete one cell cycleMitosis Overview - Mitosis results in the division of replicated chromosomes- Formation of two daughter nuclei with identical chromosomes & genes in each daughter- Usually accompanied by cytokinesisChromosomes Change During the Cell Cycle- Eukaryotic chromosomes consist of DNA associated with histone proteins- In eukaryotes, this DNA-protein material is called chromatino 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 condenseEvents in Mitosis- During mitosis:o The 2 sister chromatids separate to form independent chromosomeso One copy of each chromosome goes to each of the 2 daughter cellso Each daughter cell receives a copy of the genetic information that is contained in each chromosomeo Mitosis is a continuous process with five subphases based on specific events Prophase Prometaphase Metaphase Anaphase TelophaseProphase - 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 mitosisPrometaphase- 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 kinetocoreMetaphase- 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 plateAnaphase- 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


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