SCIENCE Q4

• Cell division


  Process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells
• Types of cell division

  • Mitosis
  • Meiosis
• Mitosis


  • Occurs in somatic cells (body cells)
  • Takes place in all types of cells (skin, muscles, lungs, gut, and hair cells) that are not involved in the production of gametes (sex cells)
• Meiosis


  • The type of cell division for the production of gametes in sexual reproduction
• In both mitosis and meiosis, the nucleus divides and may end in cytokinesis
• Human development shows the importance of cell division
• Tissues with different cell division rates

  • Lining of the stomach is replaced every five days
  • Bones (adults) & connective tissues divide less frequently
  • Skin cells shed off and are replenished daily
  • Red blood cells replaced every 120 days
  • Wound & sunburn skin heal
  • Nails & hair become longer
• Nucleus


  • Control center of the cell
  • Contains DNA (replicate prior to cell division)
• DNA (deoxyribonucleic acid)


  Double-stranded nucleic acid that is tightly coiled around proteins called histones, to form chromosomes
• Nucleotide


  A molecule that is the basic building block of the nucleic acids DNA and RNA
• DNA Replication


  Makes a copy of itself called a duplicate
• Genes


  Long coded messages that control a particular trait, such as texture or function
• Mitosis


  • Ensures that the daughter cells receive the exact copy of the DNA as the parent cells
• Centriole


  • Small cylindrical structure in the cytoplasm in most eukaryotes, but absent in plants & fungi
  • A pair of centrioles migrates & separates toward the opposite poles
  • Assists in cell division by forming spindle fibers & aster rays
• Cell Cycle


  An orderly set of events that culminates in the production of new cells
• Cell Cycle Control Points


  • Assure that the cycle is progressing as it should
• Cyclin dependent kinase (CDK)


  One of the major control switches that signals the cell to proceed from GAP 1 (G1) to synthesis (S) phase or from GAP 2 (G2) to mitotic (M) phase
• Tumor protein p53


  A protein that blocks the cycle if the DNA is damaged
• Apoptosis


  Cell death
• Phases of the Cell Cycle

  • Interphase (G1, S, G2)
  • M phase (Mitosis or Meiosis)
• G1 Phase


  • Enzyme and proteins necessary for DNA replication
  • Cells that are not dividing like muscle & nerve cells, remain at this stage throughout their life cycle
• S Phase


  • The cell replicates its DNA
• G2 Phase


  • A period of rapid cell growth and protein synthesis during which the cell prepares itself for mitosis
  • Assembly of proteins, like microtubules, which are hollow protein fibers that cause the chromosomes to move during cell division occur
• M Phase


  • The process in which the nucleus divides into two new nuclei
• Karyokinesis


  Division of the nucleus
• Cytokinesis


  Division of the cytoplasm
• Mitosis


  • A type of cell division in which the nucleus of the cell divides into two nuclei with identical genetic material
  • The resulting two daughter cells have the same number of chromosomes similar to the parent cell
  • A diploid parent cell containing 2 sets of chromosomes (paternal and maternal) results in two diploid daughter cells after mitosis
• Stages of Mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase


  • Changes in both nucleus and cytoplasm
  • The nucleolus shrinks and disappears
  • The nuclear membrane/envelope disintegrates
  • Centrioles migrate to opposite poles
  • Duplicate centrioles begin to move to the opposite poles and form spindle fiber
  • Sister chromatids start to move to the equator
• Metaphase


  • Chromosomes move and align themselves at the center of the cell called metaphase plate
  • The spindle fibers connect each chromosome on its centromere to the centrioles located at opposite poles
• Anaphase


  • The sister chromatids that make up the duplicated chromosomes separate and move toward the opposite ends
• Telophase


  • Nuclei form in both poles as new nuclear membranes form around the nuclei
  • Chromatids (now called chromosomes) are located on the opposite poles
  • The spindle fibers will dissolve and disappear
• Cytokinesis


  • The division of the cytoplasm
  • In animal cells, cleavage furrow formation occurs
  • In plant cells, cytokinesis starts at the middle of the cell and moves outward, and it's called cell plate formation
• Osteoclasts


  • Large cells, resulting in cells that have more than one nucleus
• Cell Cycle Checkpoints


  • G1 checkpoint
  • G2 checkpoint
  • M checkpoint
• G1 Checkpoint


  Ensures that the cell is ready to undergo DNA synthesis or S phase
• G2 Checkpoint


  Makes sure that the cell is mature enough to divide or undergo M phase
• M Checkpoint


  Occurs during metaphase stage of cell division, sees to it that the cell is ready to complete cell division
• Apoptosis


  A suicide of the cell where the cell destroys itself maintaining the smooth functioning of the body
• Necrosis


  Death of body tissue, can be from injury, radiation, or chemicals