Review M1&2

• No part of this lecture may be reproduced, in any form or by any means, without permission in writing by the Biology 1A03 professor Dr. Lovaye Kajiura
• Copying Biology 1A03 lecture materials for distribution, for example uploading materials to a commercial website, is strictly prohibited

  
• Copyright 2024 © L. Kajiura, McMaster University, Biology 1A03

  
• We will begin by giving honour and thanks to the Haudenosaunee and Anishanaabe nations as the traditional inhabitants of the lands where McMaster stands
• To say that is to acknowledge a debt to those who were here before us and to recognize our responsibility, as guests, to respect and honour the intimate relationship Indigenous peoples have to this land
• Mitosis


  Eukaryotic cells reproduce by this process, producing daughter cells that are genetically identical to the parent cell
• Functions of mitotic cell division

  • Growth
  • Development
  • Repair

  
• Cell cycle


  Has 4 phases: G1, S, G2, M

  
• G1 phase


  Cell growth & duplication of organelles

  
• S phase


  DNA synthesis (chromosomes are replicated)

  
• G2 phase


  Cell growth & duplication of organelles to build the protein "machinery"
• Gap phases


  Ensure the parent cell is large enough in size & has the required organelles before mitosis occurs, so the daughter cells will function normally
• Phases of mitosis


  1. Prophase

  2. Prometaphase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Cytokinesis

  
• Prophase


  • Chromatin fibers contract (DNA condenses) by tightly coiling
  • Chromosomes are visible & each consists of two identical sister chromatids joined together at the centromere
  • Mitotic spindle forms
  • Assembly of microtubules begins in the centrosome (animals) and the microtubule organizing centre (plants)
  • In animals, the centrioles begin to move apart to opposite sides of nucleus (2 poles)

  
• Prometaphase


  • Chromosomes do not appear completely aligned or organized
  • Spindle fibers attach to sister chromatids at the kinetochore regions

  
• Metaphase


  • Chromosomes line up along the Metaphase Plate
  • Centromeres are aligned on the metaphase plate, which is located equidistance from the two poles

  
• Anaphase


  • Binding proteins between the sister chromatids break down
  • Centromeres of sister chromatids disjoin & segregate, this process is called Disjunctional Segregation
  • Chromosomes move centromere first (they appear V shaped)
  • Cell elongates
• Telophase


  • Nonkinetochore microtubules further elongate the cell
  • Two daughter nuclei form
  • Formation of the nuclear envelopes around each set of chromosomes

  
• Cytokinesis


  • In animals, slime molds, & fungi, a cleavage furrow forms
  • In plants, a cell plate forms

  
• The 2001 Nobel Prize in Physiology & Medicine was jointly awarded for discoveries of the key regulators of the cell cycle
• Cyclins


  Proteins that oscillate in concentration during the cell cycle and control cyclin dependent kinase (CDK) activity
• CDK (Cyclin Dependent Kinase)


  Protein kinase that uses ATP to add phosphate groups to proteins, inducing conformational changes, and must be attached to cyclin to be active
• Cell cycle checkpoints


  • Molecular mechanisms that regulate the cell cycle
• Origins of replication (ori sites)

  Specific points where DNA replication begins, where the DNA double helix opens up to form 2 single strands and replication forks spread in both directions
• Leading strand


  Continuous synthesis, grows in 5' to 3' direction, new nucleotides added only to 3' end
• Lagging strand


  Discontinuous synthesis, grows in overall direction of 3' to 5' direction, produced by Okazaki fragments that individually grow in 5' to 3' direction
• Ligase


  Catalyzes the formation of phosphodiester bonds joining the new Okazaki fragments in the growing lagging strand
• The Meselson Stahl experiment supported the semiconservative DNA replication model