4.2 Chromosomes and Replication

• What are chromosomes made of?

  DNA and proteins
• How many chromosomes are in a human cell?

  46 chromosomes
• Why are most genes in chromosome pairs identical?

  They are inherited from both parents
• What role do histones play in chromosomes?

  They help package DNA tightly
• What happens to DNA when it is tightly packaged?

  It cannot function as a template
• What do regulatory proteins do to histone packaging?

  They decondense the histone packaging
• What are chromatids?

  Duplicated chromosomes still attached
• What is the function of centrioles during mitosis?

  They help organize the mitotic apparatus
• What is a centrosome?

  A pair of centrioles and material
• What causes centrioles to move apart before mitosis?

  Polymerization of protein microtubules
• What is the aster in mitosis?

  A spiny star formed by microtubules
• What is the mitotic spindle?

  Microtubules extending between centriole pairs
• What are the stages of mitosis?

  1. Prophase
  2. Prometaphase
  3. Metaphase
  4. Anaphase
  5. Telophase
• What happens to chromosomes during prophase?

  They condense into well-defined structures
• What occurs during prometaphase?

  Nuclear envelope fragments and microtubules attach
• What happens during anaphase?

  Chromatids are pulled apart at centromeres
• What is the equatorial plate in metaphase?

  Line where chromatids align in the cell
• What occurs in telophase?

  New nuclear membranes form around chromosomes
• What causes the cell to pinch in two during cytokinesis?

  Formation of a contractile ring of microfilaments
• What proteins are involved in the contractile ring during cytokinesis?

  • Actin
  • Myosin