cell membrane

• cell membrane

  • the "plasma membrane"
  • surrounds the outer edge of the cell
  • separating the interior of the cell from it surroundings
• transport proteins are often responsible for controlling passage across cellular membranes
• Specialized lipids are also known as Phospholipids
• Phospholipids

  • fats
  • essential structural components
  • abundant lipid
  • ampiphatic molecules
• hydrophobic tails are sheltered inside the membrane
• hydrophilic head

  • water-loving part
  • phosphate group
• hydrophobic tails

  • long hydrocarbon chains
  • fatty acids
  • do not mix well with water
• Fluid mosaic model

  • widely accepted
  • describes the structure of biological cell membranes
  • dynamic and flexible
  • the membrane is a mosaic of protein bobbing in a fluid bilayer of phospholipids
• protein

  • come in different types
  • not randomly distributed in the membrane
• Integral proteins

  • helps transport large molecules across the cell membrane
  • penetrate the hydrophobic interior of the lipid bilayer
  • firmly embedded within the lipid bilayer
  • have hydrophobic regions
  • portions exposed on both sides of the membrane.
• Peripheral

  • involved in the communication
  • not embedded in the lipid bilayer
  • loosely bound to the surface of the membrane
• Glycoproteins

  • plays an important role in cell recognition
• Fluidity

  • critical characteristic that plays a role in the structure and function of a biological cell
  • dynamic and flexible in the nature of lipid layers
• • membranes are held together mainly by weak hydrophobic molecules
  • most lipids can move sideways within the membrane
  • rarely, a lipid may flip-flop across the membrane
• quick mixing of fluorescent - proteins in the surface of the cell are NOT fixed in place
• Temperature

  • increases, so does phospholipid bilayer fluidity

  Lower temperatures

  • do not much have kinetic energy
  • cluster more together closely

  High temperatures

  • have enough kinetic energy
  • overcome the intermolecular forces holding the membranes together (increases membrane fluidity)
• Saturated

  • single bond
  • straight
  • unkinked tails

  Unsaturated

  • double bond
  • crooked and kinked tails
• cholesterol

  • randomly distributed
  • helping the bilayer stay fluid in different environmental conditions
  • holds the phospholipid together (don't separate)

  Without cholesterol

  • cells will get closer (when it's cold)
  • making it more difficult for small molecules (like gases to squeeze in between the phospholipids)
  • phospholipid leaves gap
• What is one function of membrane proteins related to transport?

  They may provide a hydrophilic channel selective for a particular solute.
• How do transport proteins function in the membrane?

  They span the membrane and create a hydrophilic channel for specific solutes.
• What role do membrane proteins play in enzymatic activity?

  They may act as enzymes with active sites exposed to adjacent substances.
• What is the significance of the active site in membrane proteins?

  The active site allows the protein to interact with substances in the adjacent solution.
• What is signal transduction in the context of membrane proteins?

  A membrane protein may bind to a chemical messenger, like a hormone.
• How does a membrane protein change shape during signal transduction?

  The binding of a chemical messenger causes the protein to change shape, relaying the message inside the cell.
• What is one function of membrane proteins related to cell-to-cell recognition?

  They help in identifying and recognizing adjacent cells.
• How do membrane proteins facilitate intercellular joining?

  Membrane proteins of adjacent cells may hook together.
• What is the role of membrane proteins in attachment to the cytoskeleton and extracellular matrix?

  They provide anchorage for the cell structure.
• What are the main functions of membrane proteins?

  • Transport: Provide hydrophilic channels for specific solutes
  • Enzymatic activity: Act as enzymes with active sites
  • Signal transduction: Bind chemical messengers and relay messages
  • Cell-to-cell recognition: Identify and recognize adjacent cells
  • Intercellular joining: Hook together with adjacent cells
  • Anchorage: Attach to cytoskeleton and extracellular matrix