Bio

• Cell Cycle

  Sequence of growth and division
• Cell Cycle


  • Divided into 2 distinct stages
  • A period of growth between cell divisions known as interphase
  • A period of cell division
• Interphase


  Time of growth and development
• Interphase


  • Cells conduct normal cell operations - protein synthesis, respiration, digestion etc.
  • Cells remain in interphase until they either divide or die
• Cell Cycle - Interphase

  1. First Growth Phase G1 (Gap 1)

  2. DNA Synthesis-S Phase

  3. Second Growth Phase (G2) Gap 2
• G1 (Gap 1)


  During G1 the cell grows rapidly while carrying out its normal life functions
• G1 (Gap 1)


  • Some cells stop here
  • Muscle cells, nerve cells and red blood cells don't divide
  • Cells that divide move on to the S phase
• DNA Synthesis-S Phase

  Replication occurs producing 2 identical copies of DNA, one complete set for each of the daughter cells produced during cytokinesis
• G2 (Gap 2)


  Preparation for cell division
• G2 (Gap 2)

  • Additional organelles like mitochondria are produced for the new cells that will result from cell division
  • The cell makes and assembles microtubules which form the spindle
  • Spindle fibers move the DNA during mitosis
  • G2 is the shortest part of interphase lasting between 4-5 hours
• Cell division


  1. Mitosis

  2. Cytokinesis
• Mitosis


  Division of the cell's nucleus, ensures each daughter cell has a complete set of DNA
• Cytokinesis


  Division of the cell's cytoplasm, occurs simultaneously with the end of mitosis
• Cell Cycle - Checkpoints

  • Each checkpoint ensures the cell is prepared for the next step
  • Many proteins control the cell cycle
  • Enzymes check and repair cells before they can move past a checkpoint
• Cancer


  Unregulated cell division, occurs when the genes that control cell division are damaged
• Cancer


  • Some cancers occur when the proteins that control cell division aren't produced
  • Other cancers occur when proteins are produced that speed up the cell cycle
  • Some of these proteins prevent damaged cells from dying
• Mitosis


  1. Each cell produced needs a complete set of DNA

  2. Divides DNA precisely into 2 new cells
• Humans


  • 46 chromosomes
  • After S phase the cell has 92 chromosomes
  • Mitosis divides them precisely so each cell has 46 chromosomes
• Chromosome


  Single very long strand of DNA supported and packaged by proteins (histones)
• DNA - Interphase


  Uncoiled and referred to as chromatin
• DNA - Mitosis


  Undergoes supercoiling and becomes tightly packed X-shaped structures called chromosomes
• Centromere

  Central constricted region of a chromosome that serves as an attachment point for the machinery of mitosis
• Sister chromatids


  Two identical DNA molecules that make up a chromosome
• Spindle fibers


  • Network of microtubules that extend across the cell
  • Provide a framework for the chromosomes to move on
  • Attach to the chromosome at the centromere
• Centrosome


  Structures in animal cells that anchor the ends of the spindle, made of 2 bundles of microtubules called centrioles
• Prophase


  1. Chromosomes supercoil

  2. Nuclear envelope dissolves

  3. Centrioles move to opposite ends of the cell

  4. Spindle starts to form
• Metaphase

  Chromosomes line up along the middle of the cell (equator)
• Anaphase


  Chromosomes divide at the centromere, sister chromatids pulled to opposite poles by the spindle
• Telophase


  1. Chromosomes uncoil back to chromatin

  2. Spindle disintegrates

  3. Nuclear envelope re-forms around the two sets of chromosomes

  4. Cytoplasm is divided into 2 separate cells (cytokinesis)
• Cytokinesis - Plant cells

  New cell wall made of cellulose forms between the 2 new nuclei
• Cytokinesis - Animal cells

  Ring of microfilaments forms around the inside of the cell membrane and pinches the cell in half
• The cytoplasm contains various structures such as mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, cytoskeleton, and centrioles.
• Mitochondria are responsible for producing energy through cellular respiration.
• The nucleus is the control center of the cell, containing genetic material (DNA) that determines an organism's characteristics.
• The cytoplasm contains various structures such as ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, cytoskeleton, and centrioles.
• Genes are segments of DNA that contain instructions for making specific proteins or controlling other genes.
• Mitochondrion - Site of aerobic respiration where energy is produced through oxidative phosphorylation.
• Mitochondria are responsible for producing energy through aerobic respiration.
• Endoplasmic Reticulum helps with protein production and transport within the cell.
• Endoplasmic Reticulum (ER) is involved in protein synthesis and lipid metabolism.