BIOLOGY 220 LECTURE #23 - Mitosis Meiosis and Asexual Animal Reproduction - 11-20-07

BIOLOGY 220 LECTURE #23 - Mitosis Meiosis and Asexual Animal Reproduction - 11-20-07

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BIOLOGY 220 – LECTURE #23 – MITOSIS, MEIOSIS, AND ASEXUAL ANIMAL REPRODUCTION CELL DIVISION – 3 What is the purpose of cell division (3 Purposes)? o New cell to increase population size o Use division for growth or tissue replacement (multicellular organisms) o All cells are genetically identical (clonal) to each other and to the original cell This means that variation in cells can only occur through mutations Asexual reproduction maintains genetic status quo If your population looks a certain way, that means the individuals in the population are going to stay the same (look the same, genes will be the same) CELL DIVISION – 4 What is the process? Good summary: DNA is first replicated and then divided equally between resulting two cells Binary fission : Cell division process in prokaryotes o Bacteria have a ring of DNA as a chromosome – replicate that ring, pinch in the cell, we end up with 2 cells Eukaryotic cells have a nucleus – its DNA is enclosed by a membrane, complexity of the DNA structure. Mitosis : Nuclear division during cell division in eukaryotes o This is different from prokaryotes
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CELL DIVISION – 5, 6 Binary Fission – prokaryotes ( the steps to making a new “you” ) - Major starting point – Green – Origin of replication o Enzymes go to work at the origin of replication, copying the information held in the DNA strain – as the copying takes place, you are building a new double stranded DNA ring - Red spot – Terminus - The DNA rings start to migrate towards the poles of the cell - The cell is elongating - KEY RESULT: 2 identical daughter cells - We call them daughter cells because we can’t tell which cell was the cell with the original DNA and which is the new copy - In binary fission , we call the separation of the two cells the formation of septum , NOT cytokinesis . CELL DIVISION: MITOSIS IN ANIMALS - 7 Oftentimes, mutations are spontaneous changes in the DNA sequence MITOSIS – Takes place in eukaryotes o Process of copying your cells CELL DIVISION - 8 Chromosome Structure Start with DNA double-helix o 1 st step: Wrap the DNA around a protein called Histone core “Wrapping thread around a spool” This DNA-histone complex is called a Nucleosome o 2 nd step: We pack nucleosomes into units called Solenoids o 3 rd step: Wrap solenoids around scaffold proteins o 4 th step: Chromatin loops are eventually wrapped into the structure of a chromosome (X-Shaped structure!) o We do this so that DNA can fit in the nucleus o We only see the chromosome (the most condensed form) when the cell is getting ready to do mitosis
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CELL DIVISION – 9 Chromosome Replication Humans and other mammals are called diploid organisms. o
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BIOLOGY 220 LECTURE #23 - Mitosis Meiosis and Asexual Animal Reproduction - 11-20-07

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