Cell Reproduction & Differentation

• Mitosis involves four stages: prophase, metaphase, anaphase, telophase, and cytokinesis.
• Prophase is the first stage of mitosis where chromatin condenses into visible chromosomes, spindle fibers form between centrosomes, nuclear envelope breaks down, and centrioles move to opposite poles.
• Metaphase is the second stage of mitosis where chromosomes align at equatorial plate (metaphase plate) along microtubules of spindle fiber.
• The cell cycle includes two phases: the interphase and the mitotic phase.
• Interphase means "in between cell division"
• Long growth period between cell division is interphase
• G1 or First Gap is the Primary period of cell growth.
• • Protein synthesis, organelles produced, and increased volume of the cytoplasm in First Gap
• G1 takes 5-6 hrs
• The checkpoint in G1 is Checking of cell size, amount of nutrients, number of organelles, and the presence of growth factors.
• S (SYNTHESIS) 

  • DNA is duplicated. Growth continues slowly. 
  • Replication (DNA), Transcription (mRNA), Translation (Protein)
  • Takes 10-12 hours. 
• 1. Replication: copying the cell’s DNA prior to cell division.
• 1. Transcription: creating a coding message of a single gene that can be carried out of the nucleus.
• Translation: converting the coded message into proteins useful to the cell.
• both transcription and translation occur all throughout an interphase called Gene Expression.
• G2 (SECOND GAP)

  • Cell prepares for division. Growth continues slowly. 
  • Chromatin condenses into chromosomes, plus histones. 
  • Semi-conserved. 
  • Takes 4-6 hours.
• Checkpoint of G2 is the point where the cell checks that all the DNA damage has been repaired
• G0 checks for DNA damage and initiates cell cycle checkpoints if necessary
• in G0, Cells that lack nutrients enter this stage and may undergo apoptosis
• Cyclin Kinases - a protein/enzyme that regulates cell division, the cell cycle, cell regulation, and signals whether a cell can proceed to the next phase.
• • Platelet-Derived Growth Factor (PDGF) - signals wound healing for fibroblasts.
• • Density-Dependent Inhibition - results from the restriction of cell density. (process)
• M phase or Mitotic Phase is Cell division regulated by proteins and enzymes. 
• • Unicellular cell division for reproduction
• • Multicellular cell division for growth and development or repair and renewal.
• Checkpoint in M phase Checking for kinetochore attachment and alignment
• Checkpoint in M phase occurs in Metaphase
• • Cells stop dividing when condensed, but if cell division continues, tumors may arise, and they may be benign or malignant. 
• Mitosis is Asexual reproduction.
• In mitosis, Daughter cells are genetically identical to the parent cell. 
• Mitosis Generates new diploid cells
• • Cytokinesis is Cytoplasm division, 2 daughter cells are formed
• G₂ (Second gap) - preparation for DNA.
• Homologous chromosomes -  are pairs of chromosomes in a diploid organism that have similar genes
• Synapsis is the process where, during the pachytene phase of prophase I in meiosis I, two homologous chromosomes come together and align themselves lengthwise.
• • Chiasmata It represents the site of crossing over.
• • Cohesin It holds the sister chromatids together
• • In Meiosis I 1 diploid cell to 2 haploid cells, crossover.
• • Daughter cells are genetically different from parent cells is meiosis
• • G₂ (Second gap)- Preparation to cell division, chromatin condenses into chromosomes.