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Divide and Conquer Lecture- BIo.doc

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Western University
Biology 1201A
Richard Gardiner

September 19, 2012 Divide and Conquer What do all cells require to survive? • A complete set of genetic instructions • Produce required molecules • Direct life processes • Genetic instructions are coded in the DNA of cells Why do cells divide? • Growth • Repair • Development Cell Cycle Activites of a cell from one cell division to the next • Cell grows, adding more cytoplasmic constituents • DNA is replicated • Cell divides into two identical daughter cells Essential Features of Cell Division • Transmit a complete copy of genetic information (DNA) • Transmit materials necessary for cell to survive and use genetic information Prokaryotic Cell • No nucleus – genetic material (DNA) in cytoplasm • No membrane-bound organelles • Example: bacteria • Cell division is called binary fission Prokaryotic Cell Cycle • Prokaryotic chromosome a circular loop • Chromosome attaches to one point on plasma membrane • Chromosome is replicated –replicated chromosome attatched to plasma membrane at a different nearby point • Cell elongates – new plasma membrane is added between chromosomes, pushing them towards opposite ends of cell • Plasma membrane grows inward at middle of cell • Parent cell is divided into two identical daughter cells Eukaryotic Cell • Membrane-bound organelles, including a nucleus • Genetic material (DNA) contained within the nucleus • Examples: fungi, protists, plants, animals • Cell division of somatic cells called mitotic cell division • Eukaryotic Chromosomes: contrain almost all the genetic information –mitosis only deals with nuclear chromosomea – Mitochondria and chloroplasts also have some DNA –DNA replication gere is handled differently Chromosomes • Chromosomes =long thread like structures • Highly condensed during mitosis • DNA + protein • Contain most of the organisms genetic information • #varies with species Eukaryotic Chromosome Structure • Strands of linear DNA • Human cells • 46 strands (46 chromosomes_ • Average length 4cm • Each strand coiled up • Human cell approx. 3 metres of DNA • Total length of DNA in an adult human approx 2 x 10^13( distance earth to sun and back) Chromatin • Many proteins are bound to DNA: • Protect • Packaging • Duplication\transcription • Regulation • Modification • DNA + bound protein =chromatin • Chromatin only about 50% DNA During non-division phase of cell cycle • DNA molecules in extended, uncondensed form=chromatin • Cell can only use DNA to produce molecules when in extended state During division phase of cell cycle • DNA molecules condense to form chromosomes prior to division • Each chromosome is a single molecule of DNA • Easier to sort and organize DNA into daughter cells What is Mitotic Cell Division? • Division of somatic cells (non-reproductive cells) in eukaryotic organisms • A single cell divides into identical daughter cells (cellular reproduction) Ploidy • Organsims have a specific number of sets in diploid and haploid cells • Mitosis and Meiosi
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