LIFE SCIENCES GRADE 10 CELL DIVISION COMPILED BY GM ZULU AND ADAPTED FROM WCDE LESSON OBJECTIVES AT THE END OF THIS LESSON YOU SHOULD BE ABLE TO KNOW THE FOLLOWING: • CELL CYCLE AND MITOSIS • CHROMOSOMES • ROLE OF MITOSIS • CANCER (BRIEF DESCRIPTION) INTRODUCTION • CELLS HAVE THE ABILITY TO DIVIDE CONTINUOUSLY • THE DIVISION OF SOMATIC CELLS, WHICH RESULTS IN GROWTH, IS KNOWN AS MITOSIS • UNCONTROLLED MITOSIS CAN RESULT IN CANCER. TERMINOLOGY • CYTOKINESIS – DIVISION OF THE CYTOPLASM, ORGANELLES AND CELL MEMBRANE • CENTRIOLES – CELL STRUCTURES THAT FORM THE SPINDLE DURING CELL DIVISION • CENTROMERE – THE STRUCTURE THAT JOINS TWO CHROMATIDS TO FORM A CHROMOSOME • METAPHASE – THE PHASE OF MITOSIS WHERE CHROMOSOMES ARRANGE THEMSELVES IN A SINGLE ROW ON THE EQUATOR. • CANCER – THE GROWTH OR TUMOUR THAT FORMS AS A RESULT OF UNCONTROLLED MITOSIS CHROMOSOMES: • CHROMOSOMES ARE THREAD-LIKE STRUCTURES FOUND IN THE NUCLEUS OF A CELL. • WHEN CELLS ARE NOT DIVIDING THE CHROMOSOMES APPEAR AS A MASS OF THREADS, THE CHROMATIN NETWORK. • A CHROMOSOME CONSISTS OF THE NUCLEIC ACID DNA AND PROTEINS • BEFORE A CELL DIVIDES, THE DNA HAS TO BE DUPLICATED. THE PROCESS DURING WHICH A DNA MOLECULE MAKES AN IDENTICAL REPLICA (COPY)OF ITSELF IS KNOWN AS DNA REPLICATION • AFTER REPLICATION HAS TAKEN PLACE THE SINGLE - STRANDED CHROMOSOME CONSISTS OF TWO STRANDS WHICH ARE CALLED CHROMATIDS. • THE TWO CHROMATIDS OF A DOUBLE-STRANDED CHROMOSOME ARE JOINED BY A CENTROMERE. THE CELL CYCLE: • THE CELL CYCLE IS THE SERIES OF EVENTS THAT TAKES PLACE IN A CELL THAT RESULTS IN DNA REPLICATION AND CELL DIVISION. • THERE ARE TWO MAIN STAGES IN THE CELL CYCLE. • THE FIRST STAGE IS INTERPHASE DURING WHICH THE CELL GROWS AND REPLICATES ITS DNA. • THE SECOND PHASE IS THE MITOTIC PHASE DURING WHICH THE CELL DIVIDES AND TRANSFERS ONE COPY OF ITS DNA TO TWO IDENTICAL CELLS. INTERPHASE • INTERPHASE IS THE PERIOD BETWEEN TWO CONSECUTIVE CELL DIVISIONS. • CELL GROWTH AND DNA REPLICATION TAKE PLACE DURING THIS PHASE. • AFTER REPLICATION HAS TAKEN PLACE, THE CHROMOSOME NOW CONSISTS OF TWO CHROMATIDS (DOUBLE-STRANDED) JOINED BY A CENTROMERE. MITOSIS FOUR PHASES CAN BE DISTINGUISHED DURING MITOSIS I.E. • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE PROPHASE • CHROMATIN NETWORK SHORTENS AND THICKENS TO FORM INDIVIDUAL CHROMOSOMES • EACH CHROMOSOME CONSISTS OF TWO CHROMATIDS JOINED BY A CENTROMERE • NUCLEAR MEMBRANE AND NUCLEOLUS DISAPPEARS • CENTRIOLES SEPARATE AND MOVE TO OPPOSITE POLES OF THE CELL • SPINDLE FIBRE FORMS BETWEEN THE CENTRIOLES METAPHASE • CHROMOSOMES MOVE TO THE EQUATOR AND ARRANGE THEMSELVES IN A SINGLE ROW ON THE EQUATOR • EACH CHROMOSOME IS ATTACHED TO THE SPINDLE FIBRES BY ITS CENTROMERE ANAPHASE • THE CENTROMERE OF EACH CHROMOSOME DIVIDES INTO TWO • THE TWO CHROMATIDS SEPARATE • THE SPINDLE FIBRE CONTRACTS AND PULLS THE CHROMATIDS TO OPPOSITE POLES • THE TWO CHROMATIDS MOVE TO OPPOSITE POLES TELOPHASE • THE CHROMATIDS NOW CALLED CHROMOSOMES ARRANGE THEMSELVES AT THE POLES • THE SPINDLE FIBRES DISAPPEAR • THE NUCLEAR MEMBRANE FORMS AROUND EACH GROUP OF CHROMOSOMES AT EACH POLE AND A NUCLEOLUS FORMS. • THE CYTOPLASM DIVIDES (CYTOKINESIS) • TWO IDENTICAL CELLS WITH THE SAME CHROMOSOME NUMBER AS THE ORIGINAL CELL ARE FORMED THE ROLE OF MITOSIS • DEVELOPMENT AND GROWTH - THE NUMBER OF CELLS INCREASES BY MITOSIS ENABLING ORGANISMS TO GROW FROM A SINGLE CELL TO A COMPLEX MULTICELLULAR ORGANISM. • REPRODUCTION - SOME ORGANISMS USE MITOSIS TO PRODUCE GENETICALLY IDENTICAL OFFSPRING. • CELL REPLACEMENT - CELLS ARE CONSTANTLY REPLACED BY NEW ONES IN THE BODY, FOR EXAMPLE IN THE SKIN. • REPLACEMENT OF DAMAGED TISSUES - SOME ORGANISMS USE MITOSIS TO REPLACE BODY PARTS. CANCER: • CANCER IS THE RESULT OF UNCONTROLLED CELL DIVISION IN THE BODY • AFTER REPEATED DIVISIONS A MASS OF TISSUE IS FORMED, WHICH IS THEN CALLED A TUMOUR • SOME CANCER CELLS ARE MALIGNANT WHICH MEANS THEY ARE ABLE TO INVADE TISSUES AND SPREAD TO OTHER PARTS OF THE BODY. • SOME TUMOURS CANNOT SPREAD TO OTHER TISSUES AND ARE CALLED BENIGN TUMOURS. BENIGN TUMOURS ARE NON-CANCEROUS. • WHEN CANCER CELLS ARE SPREAD BY THE CIRCULATION OF BLOOD, NEW TUMOURS FORM IN OTHER PARTS OF THE BODY. CANCER THAT SPREADS IN THIS WAY IS KNOWN AS METASTASIS. • AN AGENT THAT CAN CAUSE CANCER IS KNOWN AS CARCINOGEN E.G. CIGARETTE SMOKE, RADIATION, X-RAYS, UV-LIGHT, DANGEROUS CHEMICALS ETC. • THERE ARE SOME MISCONCEPTIONS ABOUT CANCER E.G. MANY PEOPLE BELIEVE THAT CANCER IS A DEATH SENTENCE, OTHERS BELIEVE THAT CANCER CAN BE PREVENTED BY EXERCISING AND EATING ORGANIC FOOD AND SOME BELIEVE THAT CANCER IS CONTAGIOUS ETC. • THE CONVENTIONAL MEDICAL APPROACHES TO TREATING CANCER INCLUDE RADIOTHERAPY, CHEMOTHERAPY AND SURGERY. THANK YOU THE END OF LESSON 7 VISIT YOUR TEXTBOOK TO GET MORE UNDERSTANDING “STAY CALM & CARRY ON”
