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BIOL 201 Chapter 10 notes

by: Kayla Wisotzkey

BIOL 201 Chapter 10 notes BIOL 201L 004

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Kayla Wisotzkey

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These notes cover Chapter 10 and include notes from the lecture and the textbook
Introduction to Cell Biology and Genetics
Dr. Sarah Texel
Class Notes
Biology, Mitosis
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This 6 page Class Notes was uploaded by Kayla Wisotzkey on Thursday October 13, 2016. The Class Notes belongs to BIOL 201L 004 at Towson University taught by Dr. Sarah Texel in Fall 2015. Since its upload, it has received 6 views. For similar materials see Introduction to Cell Biology and Genetics in Biology at Towson University.


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Date Created: 10/13/16
Chapter 10 Bacterial cell division ­Bacteria divide to reproduce, and each cell produced by cell division is an exact copy of  the original cell ­binary fission: asexual reproduction by division of one cell or body into 2 equal parts ­during binary fission, the chromosome is replicated and the 2 products are  partitioned to each end of the cell before the actual division of the cell ­Process of binary fission: 1) Prior to cell division, the bacterial DNA replicates.  This occurs in the origin of  replication 2) The replication enzymes move out in both directions from that site and make copies of  each strand in the DNA duplex.  They continue until the meet at the terminus of  replication. 3) As the DNA is replicated, the cell elongates… the DNA is partitioned in that the  origins are at the ¼ and ¾ positions in the cell and the termini are oriented towards the  middle 4) Separation begins; new membrane and cell wall material begin to grow and form a  septum at the midpoint of the cell.  A protein molecule called Fts7 facilitates this process 5) When the septum is complete, the cell pinches in two, and two daughter cells are  formed, each containing a bacterial DNA molecule ­Septum: a wall between two cavities ­Septation: the formation of a septum where new cell membrane and cell wall is formed  to separate the two daughter cells Eukaryotic chromosomes ­monosomy: human embryos missing one chromosome; usually fatal ­trisomy: human embryos that have an extra copy of one chromosome; usually fatal ­chromatin: makes up chromosomes ­composed of 40% DNA and 60% proteins ­each chromosome contains a single DNA molecule ­heterochromatin: the portion of a chromosome that is not expressed (not  transcribed into RNA) ­euchcromatin: portion of a chromosome that is expressed (transcribed into RNA) ­Chromosome structure:  ­every 200 nucleotides, the DNA duplex is coiled around a core of 8 histone  proteins ­histone proteins: positively charged because of an abundance of the amino acids  arginine and lysine; attracted to phosphate group of nucleotides ­nucleosome: the complex of DNA and histone proteins ­During mitosis, proteins are assembled into a scaffold (X­shaped) ­karyotype: the particular array of chromosomes an individual organism possesses;  viewed with a light microscope ­haploid (n): having only one set of chromosomes ­diploid (2n): having two sets of chromosomes ­homologue: one pair of chromosomes of the same kind located in a diploid cell ­Chromosome replication: ­cohesins: protein complexes that hold sister chromatids together during cell  division ­sister chromatids: one of two identical copies of each chromosome still linked at  the centromere  Overview of the Eukaryotic cell cycle ­cell cycle: the repeating sequence of growth and division through which cells pass each  generation  ­Requires the duplication of the genome, its accurate segregation, and the division of cellular contents ­5 phases of the cell cycle: 1) G1: gap phase 1, primary growth phase of the cell; usually the longest phase 2) Synthesis (S): the cell synthesizes a replica of the genome 3) G2: gap phase 2, the second growth phase of the cell; prepares for separation of the  newly replicated genome… during this phase, microtubules begin to form a spindle 4) Mitosis: the spindle apparatus fully assembles, binds to the chromosomes, and moves  the sister chromatids apart ­5 stages: prophase, prometaphase, metaphase, anaphase, telophase 5) Cytokinesis: the cytoplasm divides, creating 2 daughter cells ­G0 phase: the stage of the cell cycle occupied by cells that are not actively dividing;  cells sometimes pause here before DNA replication  Interphase ­centromere: a point of constriction on a chromosome that contains repeated DNA  sequences that bind specific proteins ­kinetochore: disk­shaped protein structure within the centromere to which spindle fibers  attach ­functions as an attachment site for microtubules necessary to separate the  chromosomes during cell division ­G1 and G2 segments of interphase are periods of active growth ­S phase: chromosomes replicate ­G2 phase: chromosomes condense and coil ­motor proteins: involved in the final condensation of the chromosomes that  occurs early in mitosis ­cells begin to assemble the machinery needed to later move the chromosomes to  opposite poles of the cell (spindle) ­tubulin: the protein that forms microtubules  Mitosis ­PROPHASE: the first stage of mitosis in which the condensed chromosomes become visible and appear bulky, and it ends when the nuclear envelope breaks down ­spindle apparatus: the assembly that carries out the separation of chromosomes;  composed of spindle fibers (microtubules) and formed during prophase ­in animal cells, the 2 centriole pairs formed during the G2 phase begin to move apart  (early in prophase) ­in plant cells, there are no centrioles, but a similar bridge of microtubular fibers still  forms  ­aster: an array of microtubules extending from the centrioles towards the plasma  membrane in animal cells; serves to brace the centrioles for retraction of the spindle ­the nuclear envelope breaks down and the endoplasmic reticulum reabsorbs its  components. At this point, the microtubular spindle fibers extend across the whole cell ­PROMETAPHASE: the second stage in which the spindle attaches to the kinetochores of  sister chromatids ­follows the disassembly of the nuclear envelope ­a second group of microtubules grow from the poles of the cells towards the centromeres ­those microtubules are captured by kinetochores on each pair of sister chromatids…  results in the kinetochores of each sister chromatid being connected to opposite poles of the  spindle ­each chromosome is attached to the spindle by microtubules running from opposite poles to the kinetochores of sister chromatids ­the chromosomes are pulled towards each pole… leads to a jerky motion that pulls all of  the chromosomes to the cell’s equator ­the chromosomes are arranged at the equator, with the sister chromatids under tension  and oriented towards opposite poles by their kinetochore microtubules ­two basic mechanisms to explain the force behind chromosome movement: 1) assembly and disassembly of microtubules provides the force to move chromosomes 2) motor proteins located at the kinetochore and poles of the cell pull on microtubules to  provide force     ­METAPHASE: the 3  stage of mitosis; the alignment of the chromosomes in the center of the cell  ­metaphase plate: an imaginary plane perpendicular to the axis of the spindle that passes  through the circle of chromosomes along the inner circumference of the cell ­all of the chromosomes line up on the metaphase plate… at this point, their centromeres  are arrayed in a circle, equidistant from the two poles of the cell, with microtubules extending  back towards the opposite poles of the cell ­ANAPHASE: the 4  stage of mitosis; the stage contains the separation of the sister chromatids ­begins when the cohesion proteins holding together sister chromatids at the centromere  are removed ­the sister chromatids are pulled towards the poles to which their kinetochores are  attached ­Anaphase A: the kinetochores are pulled towards the poles as the microtubules that  connect them to the poles shorten… causes the chromatids to be pulled closer to the poles of the  cell ­Anaphase B: the poles move apart as microtubular spindle fibers anchored to opposite  poles slide past each other, away from the center of the cell… the chromosomes move apart ­TELOPHASE: the last phase of mitosis when the spindle apparatus disassembles as the  microtubules are broken down into tubulin monomers that can be used to construct the  cytoskeletons of the daughter cells ­A nuclear envelope forms around each set of sister chromatids, which can now be called  chromosomes because they are no longer attached at the centromere ­the chromosomes uncoil into the more extended form that permits gene expression ­rRNA genes are re­expressed, resulting in the appearance of the nucleolus ­Animal cells: a belt of actin pinches off the daughter cells ­cleavage furrow: the constriction that forms during cytokinesis that is responsible for  dividing the cell into two daughter cells ­Plant cells: a cell plate divides the daughter cells ­cell plate: the structure that forms at the equator of the spindle that grows outward until  it reaches the interior surface of the plasma membrane and fuses with it, dividing the cell in 2 ­cellulose is then laid down on the new membranes, creating two new cell walls ­Fungi and some protists: daughter nuclei are separated during cytokinesis  Control of the cell cycle ­2 irreversible points of the cell cycle: 1) replication of genetic material 2) separation of sister chromatids ­3 check points of the cell cycle: 1) G1/S checkpoint: cell decides to divide, primary point for external cell influence 2) G2/M checkpoint: cells make a commitment to mitosis; assesses success of DNA  replication 3) Late metaphase (spindle) checkpoint: cell ensures that all chromosomes are attached to the spindle ­Cyclin­dependent kinases (Cdk’s): enzymes that phosphorylate proteins; primary  mechanism of cell cycle control ­Cdk partners with different cyclins at different points in the cell cycle ­for many years, a common view was that the cyclins drove the cell cycle… the  periodic synthesis and destruction of cyclins acted as a clock ­Now we know that the Cdk itself is also controlled by phosphorylation ­Kinase ­Phosphorylate: add a phosphate ­Phosphatase: take out a phosphate ­Anaphase­promoting complex: also called APC/C ­at the spindle checkpoint, presence of all chromosomes at the metaphase plate  and the tension on the microtubules between opposite poles are both important ­the function of the APC/C is to trigger anaphase ­marks securing for destruction; no inhibition of separase destroys cohesin ­Cancer: unrestrained, uncontrolled growth of cells  ­failure of cell cycle control  ­2 kinds of genes can disturb the cell cycle when they are mutated 1) Tumor­suppressor genes ­both copies of a tumor­suppressor gene must lose function for the cancerous  phenotype to develop ­Retinoblastoma susceptibility gene (Rb): predisposes individuals to a rare form  of cancer that affects the retina of the eye ­Rb protein: integrates signals from growth factors; role is to bind regulatory  proteins and prevent stimulation of cyclin or Cdk production 2) Proto­oncogenes: normal cellular genes that become oncogenes when mutated ­can cause cancer ­some encode receptors for growth factors, and some encode signal transduction  proteins ­Only one copy of proto­oncogene needs to undergo this mutation for  uncontrolled division to happen


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