cell cycle

• cell cycle has two phases, interphase and m-phase(mitosis)
• interphase: The cell cycle is spent 90% of the time in this phase, cell growth and preparation for cell division, three stages: G1, S, G2

  1. G1: cell growth
  2. S: DNA. is replicated
  3. G2: cytoplasmic components are doubled in prep for division
• M-phase/mitosis: division of the nucleus, five phases

  1. Prophase: DNA coils condense
  2. Metaphase: chromosomes alien across the cell
  3. Anaphase: chromosomes break, and sister chromatids move to opposite sides
  4. Telophase: nucleus reforms
  5. Cytokinesis: division of cytoplasm and/or membrane
• G-0 (G-zero): cells no longer divide but can still undergo mitosis
• frequency of cell growth varies by cell type
• interphase checkpoints: determination of whether the cell is prepared to be processed to the next phase of the cell cycle
• G1 checkpoint: cell size check, nutrient check, DNA damage check (Can DNA synthesis begin?)
• G2 checkpoint: DNA replication check, DNA damage check, sufficient organelles?, has DNA synthesis been completed?, committed to mitosis
• M spindle check: fibers attachment to the chromosome check, are all chromosomes attached to a spindle?, can sister chromatides separate correctly?
• how do cells know when to divide?

  internal signals: promoting factors

  external signals: growth factors
• cyclins: proteins associated with specific phases of the cell cycle (concentration fluctuates depending on cell activity), peaks at M-phase
• cyclins dependent kinase: a protein that phosphorylates the cyclin, always present and activates when bonded to cyclin
• cdk-cyclin complex/MPF: triggers passages through different stages of the cell
• external growth factors: protein signals released by body cells that stimulate other cells to divide
• apoptosis: promoted cell death if the cell doesn't meet requirements (ex. cancer)
• how do cells communicate?

  direct contact, local/short distance, long distance
• target cell: cell receiving message
• ligand: chemical signal molecule (ex. hormone, protein, neurotransmitter)
• direct contact: multi or unicellular organisms maintain contact with neighboring cells
• Long distance signaling: The target cell is usually different than the signaling cell (ex. hormones)
• local signaling: short distance (ex. neurons)
• signal transduction pathways: signal reception to cellular response

  1. reception: ligand binding to accepting protein
  2. transduction: series of reactions to convert signal --> response
  3. response: specific cellular response
• homeostasis: the ability to keep internal conditions in a normal range (ex. body temp, pH, blood pressure)
• feedback loops: can keep/take out of homeostasis
• pro feedback loops: removes from homeostasis, increases stimulus, happens to completion, only at certain points in life
• neg feedback loops: maintains homeostasis, response stops/inhibits the original signal