cell division

• DNA contains the genetic instructions for the development and function of living things
• The main role of DNA in the cell is the long-term storage of information
• Cell cycle: orderly set of stages from the first division of eukaryotic cell to the time the resulting daughter cells divide
• Just prior to cell division:

  • Cell grows bigger
  • Number of organelles doubles
  • DNA is replicated
• 2 major stages of the cell cycle:

  • Interphases
  • Mitotic phases
• Interphase includes:

  • G1 stage: cell increases in size, doubles its organelles, accumulates materials for DNA synthesis, carries out normal metabolic roles
  • S stage: DNA synthesis and DNA replication
  • G2 stage: cell synthesizes protein to assist cell division, DNA replication
• Mitotic stage includes:

  • Mitosis: nuclear division, daughter chromosomes distributed by the mitotic spindle to two daughter nuclei
  • Cytokinesis: division of cytoplasm, results in two genetically identical daughter cells
• Cell cycles are controlled by signaling proteins like growth factors and cell cycle checkpoints (G1, G2, and M)
• Apoptosis is caused by enzymes caspases and is essential to maintain homeostasis
• Consequences of damaged cell cycle checkpoints:

  • Cell can't control their cell growth
  • DNA damage can't be fixed
  • Damaged cells do not undergo apoptosis
• Cancer is a failure of cell division control, with cancerous cells losing checkpoints that control cell division
• Mitosis involves the separation of sister chromatids and distribution to daughter cells
• Significant events during mitosis:

  • Sister chromatids separate at centromere
  • Daughter chromosomes of each type distributed to opposite daughter nuclei
• Phases of Mitosis:

  • Prophase: spindles assemble, chromatin condenses
  • Prometaphase: kinetochores fibers attach sister chromatids to opposite poles
  • Metaphase: sister chromatids separate at centromere
  • Anaphase: chromosomes pulled by kinetochores fibers
  • Telophase: spindles disappear, daughter nuclei contain same number and kinds of chromosomes
• Cytokinesis in Animal Cells:

  • Cleavage furrow appears between daughter nuclei
  • Formed by contractile ring of actin filaments
• Cytokinesis in Plant Cells:

  • Rigid cell wall builds new cell wall between daughter cells
  • Golgi apparatus sends vesicles filled with cell wall building materials to center
• Cancer is a cell growth disorder that occurs when cells divide uncontrollably
• Characteristics of Cancer:

  • Lack of differentiation
  • Have abnormal nuclei
  • Do not undergo apoptosis
  • Forms tumor
  • Undergo metastasis and angiogenesis
• Meiosis is a nuclear division that reduces chromosome number from diploid to haploid
• Meiosis is used only for sexual reproduction
• Chromosomes replicate in interphase before entering Meiosis I and then halved prior to fertilization
• Homologous chromosomes occur in pairs and consist of paternal and maternal homologues
• Diploid body cells have chromosomes in pairs, similar in size and shape, carrying the same genes
• Chromosomes carry the same genes
• Consist of paternal and maternal homologues with the same gene locus
• Each chromosome is composed of two chromatids
• Sister chromatids contain exactly the same genes
• Non-sister chromatids contain genes of the same traits
• Homologue copies of a gene may encode identical or different genetic information
• Variants of a gene are called alleles
• Identical alleles on both homologues result in homozygous individuals
• Different alleles on both homologues result in heterozygous individuals
• Meiosis is known as reduction division because it reduces the number of chromosomes from 2n to n
• Occurs in gametes (sex cells) during the production of sperms and ovum
• Requires two nuclear divisions: the first division separates each homologous chromosome and reduces the chromosome number, the second division separates sister chromatids
• Homologous chromosomes come together and line up side by side forming a synaptonemal complex
• Homologous chromosomes align at the metaphase plate and segregate, reducing the chromosome number by half
• Genetic variation is essential for species to evolve and adapt in a changing environment
• Genetic recombination occurs through crossing over between homologous chromosomes and independent assortment of homologous chromosomes
• Crossing over in meiosis I produces genetic recombination/variation by exchanging gene segments at chiasma points