mitosis meiosis

• Cell Cycle


  Series of events that involve cell growth and cell division
• Chromosomes


  • Carry the genes of organisms, which are responsible for the observed characteristics
  • A structure found inside the nucleus of a cell
  • A chromosome is made up of proteins and DNA organized into genes
  • Each cell normally contains 23 pairs of chromosomes
• DNA


  • Deoxyribonucleic acid
  • Genetic material of the cell
• Four Phases of Cell Cycle


  1. G1 or GAP 1

  2. S (Synthesis) Phase

  3. G2 or GAP 2

  4. M (Mitosis/Meiosis) Phase
• G1 or GAP 1

  • Longest phase
  • Rapid growth until the normal size is reached
  • Organelles are formed
  • Proteins (enzymes) needed for the S phase are produced
  • Cells that do not divide (muscle and nerve cells) remain at this stage throughout their life cycle
• S (Synthesis) Phase


  • DNA doubles through replication
  • At the end of this stage, each chromosome is made up of two sister chromatids attached to the centromere
• G2 or GAP 2


  • Preparations for cell division
  • Assembly of proteins such as microtubules that cause the chromosome to move during cell division
• M (Mitosis/Meiosis) Phase


  • The cell undergoes division
  • Division of the nucleus is called karyokinesis, while the division of the cytoplasm is called cytokinesis
• Cells spends most of its time in INTERPHASE (around 90 percent)
• Interphase


  The phase of the cell cycle during which a cell is neither dividing nor preparing to divide
• Sister Chromatids


  Two identical copies of the same chromosome formed by DNA replication, attached to each other by a structure called centromere
• Kinetochore


  A disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart
• Diploid Cells


  A cell having 2 copies of each chromosome. A zygote that forms from the fertilized egg has 46 chromosomes. 23 chromosomes from the egg cell of the mother and 23 chromosomes from the sperm of the father
• Haploid


  Refers to the number of chromosomes in egg or sperm cells. Each gamete has 23 chromosomes each. When they unite, they form a diploid cell
• Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell's DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals
• Mitosis


  • Division of body cells or Somatic cells
  • A type of cell division in which the nucleus of the cell divides into two nuclei with identical genetic material
  • It only occurs in eukaryotes
• Four Stages of Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Prophase


  • The long, threadlike chromatids during interphase start to coil and become visible under a compound microscope as individual chromosomes
  • The chromosomes appear condensed, and the nuclear envelope is not apparent
• Metaphase


  • Chromosomes line up at the metaphase plate
  • Each sister chromatid is attached to a spindle fiber originating from the opposite poles
• Anaphase

  • Chromosomes split into two
  • Sister chromatids are pulled toward opposite poles
  • Spindle fibers elongate
• Telophase


  • Chromosomes arrive at opposite poles and begin to decondense
  • Nuclear membrane starts to re-appear
  • Spindle continues to push the poles apart
  • Two new identical daughter cells
• Meiosis


  • Division of sex cells or gametes
  • Produces cells with half the number of chromosomes as the original cell
• Stages of Meiosis I


  1. Prophase 1

  2. Metaphase 1

  3. Anaphase 1

  4. Telophase 1
• Prophase 1


  • Chromosomes start to coil and shorten
  • Nuclear envelope disintegrates
  • Homologs pair up through synapsis
  • Crossing over, which contributes to genetic variability, may occur between homologs when chromatids are broken
• Metaphase 1


  • Homologs align at the metaphase plate
  • Homologs attach to spindle fibers through kinetochore in the centromeres
• Anaphase 1


  • Homologs separate
  • Chromosomes move toward opposite poles through the spindle fibers
• Telophase 1


  • Chromosomes reach opposite poles
  • Cleavage furrow appears and the cytoplasm starts to divide
  • In most organisms, the nuclear membrane forms
• Stages of Meiosis II


  1. Prophase 2

  2. Metaphase 2

  3. Anaphase 2

  4. Telophase 2
• Prophase 2


  • Nuclear membranes disintegrates
  • New spindle fibers form around the chromosomes
• Metaphase 2


  • Chromosomes align at the metaphase plate and attach to spindle fibers through the kinetochore in their centromeres
• Anaphase 2


  • Each chromosome divides into two sister chromatids
  • Chromatids move toward opposite poles
• Telophase 2


  • Nuclear membrane forms around each set of chromosomes
  • Spindle fibers disintegrate
• Mitosis


  Division of body cells or Somatic cells
• Meiosis


  Division of sex cells or gametes