cell communication

• What have biologists discovered regarding cellular regulation?


  Some universal mechanisms of cellular regulation
• What determines a cell's response?


  The combined effects of multiple signals
• What do microbes reveal about cell signaling?


  They provide insight into the role of cell signaling in the evolution of life
• What is the role of external signals in cells?


  They are converted to responses within the cell
• In which type of cells was cell communication first studied?


  Yeast cells
• How do yeast cells find and identify their potential mates?


  Through signal transduction pathways
• What is a signal transduction pathway?


  • A series of steps converting a signal on a cell's surface into a specific cellular response
  • Begins when a signal arrives at the cell surface
  • Involves multiple steps inside the cell
• What do pathway similarities suggest about ancestral signaling molecules?


  They evolved in prokaryotes and were modified in eukaryotes
• What allows bacteria to detect population density?


  The concentration of signaling molecules called autoinducers
• What does signaling in bacteria lead to?


  A coordination of activities, allowing them to act like a multicellular organism
• How do cells in a multicellular organism communicate?


  • By chemical messengers
  • Communication varies based on distance between cells:
  • Direct contact
  • Local signaling
  • Long-distance signaling
• What connects the cytoplasm of adjacent animal cells?

  Gap junctions
• What connects the cytoplasm of adjacent plant cells?

  Plasmodesmata
• What is paracrine signaling?

  Local signaling where messenger molecules travel short distances
• What occurs during synaptic signaling?


  An electrical signal triggers the secretion of neurotransmitter molecules
• How do hormones function in long-distance signaling?


  They travel via the circulatory system to target cells
• What are the three stages of cell signaling as discovered by Earl W. Sutherland?


  1. Reception
  2. Transduction
  3. Response
• What happens during the reception stage of cell signaling?


  A target cell receives a signal molecule on the outside
• What occurs during the transduction stage of cell signaling?


  The signal molecule changes the receptor protein and starts a series of chemical reactions
• What is the response stage of cell signaling?


  Changes in the cell may regulate cytoplasmic activities or transcription of DNA
• Why is cell signaling complicated?


  It ensures proper timing of communication and activities in the right cells
• What happens when a ligand binds to a receptor?


  It generally causes a shape change in the receptor
• What type of molecules bind to specific sites on receptor proteins in the plasma membrane?


  Water-soluble/polar signal molecules
• What are the three main types of membrane receptors?

  1. G protein-coupled receptors
  2. Receptor Tyrosine Kinases
  3. Ligand-gated Ion channel receptors
• What is the function of G protein-coupled receptors?


  They work with the help of a G protein
• What do G proteins bind to?


  The energy-rich molecule GTP
• How does a G protein function as a molecular switch?


  It is either on or off depending on whether GDP or GTP is attached
• What happens when a signal molecule binds to a G protein-coupled receptor?


  The receptor changes shape and activates the G protein
• What occurs after the G protein is activated?


  It dissociates from the receptor and binds to an enzyme
• What happens to the G protein after it activates the enzyme?


  It hydrolyzes GTP to GDP and becomes inactive
• What happens when bacteria modify G-proteins?


  It ceases communication between cells
• What do receptor tyrosine kinases do?


  They form dimers and attach phosphates to tyrosines
• What is a key feature of receptor tyrosine kinases?


  They can trigger multiple signal transduction pathways at once
• What happens when a ligand binds to a ligand-gated ion channel receptor?


  The gate opens, allowing specific ions to flow through
• What is the role of ion channels in the nervous system?


  They trigger electric signals through the diffusion of ions
• Where are intracellular receptors found?


  In the cytoplasm or nucleus of target cells
• What type of chemical messengers can activate intracellular receptors?


  Small or hydrophobic chemical messengers
• What can an activated hormone-receptor complex act as?


  A transcription factor, turning on specific genes
• What are examples of hydrophobic messengers?


  • Steroid hormones (e.g., Testosterone, Aldosterone)
• What happens when the gate opens in a cell membrane?


  Specific ions can flow through the channel and change the ion concentration inside the cell.