genbio

• Cell division

  1. Parent cell divides into two daughter cells

  2. Has 2 main phases: Interphase and Mitotic phase (Mitosis or Meiosis)
• Chromatin


  Thread-like structures
• Chromatids


  Two identical threads
• Chromosome


  • Chromatin thread that becomes highly coiled and condensed during cell division
  • Most important part of the DNA
  • If damaged, can lead to mutated cells (e.g., Cancer cells)
  • Holds DNA
  • Organized & condensed structure of the DNA
  • DNA is coiled into proteins called "Histones"
  • Responsible for replication
• Centromere


  The point at which two chromatids are held together
• Long growth period during which the cell grows and DNA is duplicated in preparation for the next division
• 3 Subphases of Interphase


  • G1 phase
  • S phase
  • G2 phase
• G1 phase


  • Cells are newly divided cells
  • Period between the last cell division and DNA synthesis
  • Period of very active cell growth
  • Cells are at their smallest size at the start of G1
  • Period of very active cell growth
  • Cells are already functional and performing metabolic activity
• S phase

  • The cell's chromosomes are duplicated
  • Growth continues but at a slower pace than G1 phase
  • Longest phase occupying almost half of the cell cycle duration
  • Divided into Replication, Transcription, and Translation
  • Transcription and translation occur throughout the interphase
• G2 phase


  • Cell continues to grow slowly as it prepares for cell division
  • DNA is already duplicated with 2 copies
  • DNA is condensed and becomes chromosomes
  • Cell does not stop growing to distribute enough cytoplasm for the 2 daughter cells
  • DNA binds to histone proteins to become chromatin
  • Chromatin will coil and become folded to become sister chromatids
• G0 phase


  • Non-dividing stage for cells needing repair or tissues not requiring new cells
  • Can be temporary or permanent for the cell
• Neurons stop growing and repairing when we reach adulthood
• How Cell Reproduction is Regulated
• 3 Checkpoints in Cell Reproduction

  • G1 checkpoint: Assess integrity of DNA
  • G2 checkpoint: Assess proper chromosome duplication
  • M checkpoint: Assess attachment of each kinetochore to a spindle fiber
• Enzymes and proteins required by checkpoints

  • Cyclin kinase
  • PDGF
  • Density-dependent inhibition
• M PHASE includes mitosis and meiosis
• M checkpoint

  Attachment of each kinetochore to a spindle fiber is assessed
• Enzymes and proteins required by checkpoints

  • Cyclin kinase
  • PDGF
  • Density-dependent inhibition
• M PHASE


  1. When the cell divides into daughter cells

  2. Includes mitosis and meiosis
• Mitosis

  • Asexual cell division producing identical daughter cells
  • Shortest phase
  • All other cells
• Stage 1: Prophase

  1. Chromosomes become visible as duplicate chromosomes, consisting of sister chromatids held together by centromeres

  2. Nucleoli disappear

  3. Mitotic spindle formed from the centrosome

  4. Centrosomes migrate to cell poles

  5. Metabolic activity decreases
• Stage 1.1: Prometaphase

  1. Nuclear envelope fragments

  2. More condensed chromosomes

  3. Each chromatid now has kinetochores

  4. Some microtubules attach to the kinetochores "kinetochore microtubules"

  5. Nonkinetochore microtubules interact with those at the opposite pole of the spindle
• Stage 2: Metaphase

  1. Duplicate chromosomes form single lines at the equator between centriole poles "metaphase plate"

  2. Centrosomes are at opposite poles of the cell

  3. It lines up in the middle
• Stage 3: Anaphase


  1. Sister chromatids separate

  2. Daughter chromosomes are pulled toward poles by kinetochore microtubules

  3. Cell elongates as nonkinetochore microtubules lengthen

  4. Shortest stage
• Stage 4: Telophase


  1. Reverse of prophase

  2. Daughter nuclei forms

  3. Mitotic spindle disintegrates

  4. Chromosomes start to uncoil and revert to chromatin

  5. Moving to resting
• Cytokinesis

  1. The process by which a cell divides to produce two daughter cells

  2. A contractile ring or protein filaments forms just inside the cell membrane; it tightens and forms a cleavage furrow pinching the cell in two

  3. The ring is perpendicular to the long axis of the mitotic spindle, and it ensures that one nucleus is enclosed in each of the daughter cells
• Meiosis

  • Sexual cell division producing genetically different daughter cells
  • Type of cell division that produces gametes (egg and sperm cells)
  • Occurs in the reproductive organs (testes and ovaries)
• Meiosis characteristics

  • Generates haploid cells (one set of chromosomes per cell only)
  • Involves sex cells
  • Requires 2 cell division
  • PMAT 1 & 2: we will have 4 daughter cells by the end
• PMAT 1: Stage 1: Prophase 1

  1. Pairing up and crossing over

  2. Homologous chromosomes pair; genes aligned precisely with other homologs

  3. Chromatids lie side by side in a process called synapsis, forming a tetrad (a pair of homologous chromosomes)
• We will have 4 daughter cells by the end of PMAT 1 & 2
• PMAT 1 - Stage 1: Prophase


  1. Spindle fibers attach to chromosomes

  2. Centrioles travel to opposite poles

  3. Nuclear envelope disintegrates/disappears
• PMAT 1 - Stage 1: Prophase


  • Homologous chromosomes pair and genes align precisely with other homologs
  • Chromatids lie side by side in synapsis forming a tetrad
  • Terms: Synaptonemal Complex, Synapsis, Chiasma/Chiasmata
• PMAT 1 - Stage 2: Metaphase 1

  1. Pairs of homologous chromosomes line up along the metaphase plate

  2. Chromosomes can have several combinations due to crossing over
• PMAT 1 - Stage 3: Anaphase 1


  Centrioles pull sister chromatids towards the pole
• PMAT 1 - Stage 4: Telophase 1


  1. Cleavage furrow appears

  2. Nuclear envelope reappears

  3. Cytokinesis: separation of cytoplasm

  4. Relaxation of chromosomes
• No chromosome duplication between meiosis 1 & 2, resulting in a total of 2 cells
• PMAT 2


  • Similar to PMAT of mitosis
  • Total of 4 cells (all genetically different)
• Gametogenesis is the process by which cells undergo cell division and differentiation to form mature haploid gametes
• Spermatogenesis is the formation of sperm cells through meiosis producing 4 sperm cells
• Oogenesis is the formation of egg cells through meiosis, producing 3 polar bodies and 1 ovum per cycle; 1 germ cell produces one ovum