AP BIOLOGY- Unit 4 Cell Communication & Cell Cycle

• Synaptic signaling is a type of cell communication where neurons release neurotransmitters into the synapse to transmit signals to target cells.
• Phospholipids have hydrophilic heads and hydrophobic tails.
• Cell membranes are composed of phospholipids, cholesterol, proteins, and carbohydrates.
• The cell membrane is the outermost layer that surrounds all cells.
• Neurotransmitter receptors are proteins located on the surface or inside the postsynaptic membrane that bind with specific neurotransmitters, triggering an action potential in the postsynaptic neuron.
• The process of signal transmission involves the binding of neurotransmitters to their respective receptors, leading to changes in ion channels and subsequent depolarization or hyperpolarization of the postsynaptic membrane.
• The phosphate group on the head attracts water, while the fatty acid tail repels it.
• Cholesterol helps maintain membrane fluidity by preventing excessive packing of lipid molecules.
• The fluid mosaic model describes the structure of the plasma membrane as a dynamic and constantly changing arrangement of lipid molecules and embedded proteins.
• Cells communicate 3 ways

  direct contact, local signaling, long distance signaling
• direct contact


  communication through cell junctions
• gap junctions


  In animal cells, pores formed from connected membrane proteins that allow molecules to pass directly from cell to cell.
• Plasmodesmata


  channels through cell walls that connect the cytoplasms of adjacent cells
• target cell


  cells that have receptors for a particular hormone
• ligands


  A molecule that binds specifically to a receptor site of another molecule.
• paracrine signaling


  Signal released from a cell via exocytosis that has an effect on neighboring cells.
• synaptic signaling


  a type of local signaling specific to neurotransmitters in nerve cells
• hormones

  Chemical messengers, mostly those manufactured by the endocrine glands, that are produced in one tissue and affect another
• endocrine signaling


  A type of long-distance signaling in animals that utilizes hormones.
• example of long distance signaling


  insulin
• 3 stages of cell signaling

  reception, transduction, response
• receptor


  protein that detects a signal molecule and performs an action in response
• reception


  The target cell's detection of a signal molecule coming from outside the cell.
• transduction (cell signaling)


  converts the signal to a form that can bring about a specific cellular response
• response (cell signaling)


  the end result of a specific signaling pathway
• Examples of plasma membrane receptors

  G protein-coupled receptors (GPCRs) and ligand-gated ion channels
• Plasma membrane receptors


  bind to polar, water-soluble and large molecules
• Examples of intracellular receptors


  steroid hormones, thyroid hormones, nitric oxide
• Protein kinase


  relays signal inside the cell
• protein phosphatases


  shuts off pathways
• Second messengers


  small, non-protein molecules and ions help relay the message and amplify the response Example: cAMP
• Example responses in Signal transduction pathway

  protein that can alter membrane permeability, enzyme that will change a metabolic process, protein that turns genes on or off
• G protein-coupled receptors (GPCRs)


  - largest category of cell surface receptors- important in animal sensory systems- binds to a G protein that can bind to GTP, which is an energy molecule similar to ATP
• ligand-gated ion channel


  Type of membrane receptor that has a region that can act as a "gate" when the receptor changes shape.
• homeostasis


  relatively constant internal physical and chemical conditions that organisms maintain
• set points


  values for various physiological conditions that the body tries to maintain
• Feedback loops


  maintain homeostasis-detects and responds to changes in internal environment (positive and negative)
• Negative Feedback


  a mechanism of response in which a stimulus initiates reactions that reduce the stimulus
• Positive Feedback


  A type of regulation that responds to a change in conditions by initiating responses that will amplify the change. Takes organism away from a steady state.
• Stimulus


  a signal to which an organism responds