Cell Division - BIO2

• Interphase

  • a lot transcription and translation happens
  • A new cell is produced
  • cell is very small
  • the three phases are G1, S, G2
• Unicellular organism

  • its purpose of cell division is reproduction
• Multicellular organism

  • its purpose for cell division is development
• Phase 1: G1 = Primary Growth of Cell

  • First Gap
  • The cell needs to grow big in size (increase the volume of cytoplasm) to cater more organelles.
  • If the cell grows significantly, it will proceed to Synthesis (S Phase)
• Phase 2: S-Phase - Synthesis

  • The DNA is replicated, it is being doubled in preparation for cell division
  • the daughter cells should get an equal number of chromosomes
  • focus is already on DNA Replication
  • once the DNA is replicated, proceed to G2
• Phase 3: G2 - Preparation for Division

  • preparation for mitotic phase
  • takes 4-6 hours
  • check the DNA if it is already replicated
  • histones are combined with DNA to become nucleosomes, then to chromatin fibers, and condense to become chromosomes
• The center of a Chromosome is called centromere.
• • The edge of a chromosome is called telomeres.
• Optional Phase: G0 - Non-dividing Phase

  • There should be enough nutrients
  • There should be an increase in size
  • There should be the presence of other cells
  •  a non-dividing, temporary, or permanent phase.
• 1. Mitotic Phase (M Phase)

  • 2 major phases
  • mitosis and cytokinesis

  The cell cycle takes about 18-24 hours.
• Mitosis

  • nucleus divides
  • takes less than an hour

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
• Cytokinesis

  • cytoplasm divides
• DNA STRUCTURE AND FUNCTION

  • Transcription and translation occur throughout the interphase
• DNA replication occurs during the S Phase (Synthesis) only.
• How Cell Reproduction is Regulated

  1. Liver cells (self-healing)
  2. Neurons -it will stop dividing (permanently)
• CHECKPOINTS

  • There are proteins/checkpoints that regulate cell division
• CHECKPOINTS

  1. G1 Checkpoint
  2. G2 Checkpoint
  3. M Checkpoints
• • If G1 Requirements are met – goes to S phase
  • S phase – no requirement
  • G2 phase – it is between G2 and Mitotic Phase where DNA is checked
• M checkpoint (metaphase) 

  • To check if the spindle fibers are attached to the centromeres (should be attached)
  • If the chromatids are pulled during anaphase, both daughter cells would get the total number of chromosomes
• 1. Cyclin kinase

  • If this enzyme is absent, it might affect the regulation, checkpoints, and even cell division
• 1. Platelet-derived growth factor (PDGF)

  • release in platelets
  • For fibroblasts (wound-healing)
• Density-dependent inhibition

  • Dependent Inhibition = we will not divide anymore (prevent dividing)
  • They inhibit cell division if the cells are intact and there is no problem.
  • If the cells are not working correctly, cell division continues.
• • If there is overproduction of cells, it leads to tumors. 

  1. Benign = can be removed
  2. Malignant = it can still be removed, yet they metastasize (spread)
• Mitosis

  • Somatic cells
  • Diploid (2n)
  • 46 chromosomes
  • 1 round of mitosis
  • product of 2 sets of chromosomes (parents)
  • Asexual reproduction - nuclear division - cytoplasmic division
  • daughter cells are identical to parent cells
  • for growth and repair
  • diploid to diploid
• Binary fission - reproduction of single-celled organism
• Meiosis

  • Gametes (sex cells)
  • Haploids (1n)
  • 23 chromosomes per gamete
  • 2 rounds of meiosis - Meiosis 1 (1 diploid-2haploid and crossover) Meiosis 2 (2 haploid-4haploid)
  • genetically different from parents
  • Crossover - exchange of genes
  • Chiasmata - site of crossover
• Prophase

  • Chromatin condenses into visible and unorganized chromosomes
  • Nucleus disappears
  • Mitotic spindle formed 
  • Centromeres, microtubules, asters
  • Centrosomes migrate to cell poles
  • Only found in animal cells
  • Metabolic activity decreases
• Cohesins - Hold bivalents together during homologous recombination. It joins the sister chromatids together
• Centrioles

  • Paired barrel-shaped organelle inside the centrosome; Made up of nine microtubules (organizes it). Determine the location of the nucleus and organelles. 
• Centromeres - Protein; links a pair of sister chromatids together during cell division 
• Chromatin

  • Folds nucleosomes (combined DNA & Histones) that become fibers. This condenses to become chromosomes.
• Chromosome

  Contain genes/traits that are important for cell division.
• Chromatids

  One of the two identical halves of a chromosome that have been replicated in preparation for cell division.
• Kinetochore

  Protein; Kinetochores serve as the sites of attachment of spindle fibers to the centromeres. prometaphase congression. microtubule binding
• Microtubules

  Have three types: polar, kinetochore, and astral. Extend outward from duplicated centrosomes to form the mitotic spindle–for the separation and distribution of chromosomes to daughter cells.
• Spindle Fibers

  Long strands of protein; Are microtubules; move to each side of the cell. They extend out microtubules that are used to pull the chromosomes. 
• Prometaphase

  • Nuclear membrane is already gone
  • Chromosomes are already in the cytoplasm
  • Kinetochores are already prepared for attachment
  • some microtubules attach to the kinetochore – “kinetochore microtubules”
• Metaphase

  • Alignment of chromosomes
  • Duplicate chromosomes form a single line at the equator (middle) between Centriole poles “metaphase plate”
  • Centrosomes are at opposite poles of the cell
  • M Checkpoint
• Anaphase

  • Pulling of sister chromatids toward the opposite poles; separate
  • Mitotic spindle formed 
  • Centromeres, microtubules, asters
  • Centrosomes migrate to cell poles
  • Only found in animal cells
  • Metabolic activity decreases
• 1. Telophase

  • Formation of Nuclear Membrane 
  • Reverse of prophase
  • Nuclear membrane reforms
  • Nucleoli reappear
  • mitotic spindle disintegrates
  • chromosomes start to uncoil and revert to chromatin
  • forming of cleavage furrow for animals
  • formatting of cell plate for plants