Cell Signaling and Cell Cycle

• Cell Signaling

  • Cells need to communicate to maintain homeostasis

  • Used to react to changes 

• Short distance signaling

  • Cells have to be touching each other for this type of signaling

  • Fastest type of signaling

  • Happens in spaces between cell membranes

    • Gap junctions = animals

• Long Distance Signaling

  • involves the release of ligands

  • Can travel short distances through diffusion or long distances in the bloodstream

  • Requires specific receptors to activate response in another cell

• 3 steps of cell signaling

• 1 = Reception

  • Ligand binds to receptor embedded in cell membrane (like enzymes or puzzle pieces!)

• Small, non-Polar ligands pass through the membrane to receptors in the cell

• Shape change transmits signal into the cell

• 2 = Transduction

• Signal is moved from the cell membrane  to the nucleus (Can be done by secondary messenger)

• Done by phosphorylation (adding phosphates) of a series of proteins

  • Phosphates moved from ATP to other molecules by kinase

• Ligands that bypass the cell membrane can go straight to nucleus bypassing transduction

• 3 = Response

  • Signal changes a section of the genes to affect the protein being made

  • Creation (of stopping the creation) of a protein triggers the cell response 

• Effects of signals

  • Initiation of gene expression (making proteins)

  • Cell growth and differentiation

  • Creation of other molecules (insulin, steroids)

  • Initiate cell death (Apoptosis)

  • Pathways allow cells to adapt to and react to changes in environment

• Mutations t signaling proteins can alter or stop signal pathways

  • Shape is everything for a protein so if the protein changes the pathway changes

• Feedback

  • Reactions cells have to signals

  • Two types:

    • 1= Negative Feedback- signal causes the cell to force changes to stop the effect of the signal (insulin in response to blood sugar)

    • 2= Positive Feedback- signal causes cell to amplify effect of signal until signal is stopped (contractions during birth)

  
  

• Cell Cycle

  • Cell cycle is made of interphase and division

    • Interphase

      • G0-G1= Growth phase

        • Cell is doing its job, gathering resources, growing

      • S phase= DNA Replication

        • Cell goes from 2n-4n

      • G2- Growth phase 2

        • Cell checks for errors, ensures it is ready for division and that division needs to happen

      • Healthy cells spend MOST of their lives in interphase

      • Regulated by interactions between cyclins and cyclin-dependent kinases (CdK’s)

• Mitosis

  • Cell division used by somatic cells and for asexual reproduction

    • Important for tissue repair, blood cells, immune response

  • Makes IDENTICAL copies

  • 2n→2n

  • 5 parts

    • Prophase

      • Nuclear membrane dissolves

      • Nucleolus dissolves

      • DNA condenses into chromosomes

    • Metaphase

      • Chromosomes line up in the middle of the cell

        • Pushed into place by spindle fibers

        • Spindle fibers attach to centromere

• Anaphase

  • Chromatids are pulled apart to opposite sides of the cell

• Telophase

  • Two nuclei form

    • Two new cells are still connected by the cytoplasm and membrane

• Cytokinesis

  • Cuts the cell in two

• Chromosomes

  • Condensed DNA

  • Two chromatids connected to a centromere

    • For mitosis each chromatid is identical

    • In meiosis the chromatids are different because of crossing over

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• Cancer

  • Uncontrolled mitosis

  • Caused by RANDOM mutations that affect cyclins and cyclin dependant kinases

  • Only affect somatic cells

  • Causes cells to spend less time in interphase