Cell membranes

• What is the structure of the cell membrane primarily composed of?

  Phospholipid bilayer
• What property of the membrane allows lipid-soluble substances to enter or leave the cell?

  The flexibility and self-sealing nature of the phospholipid bilayer
• Why can't water pass through the phospholipid bilayer?


  Because of the hydrophobic tails of the phospholipids
• What are intrinsic proteins?


  Proteins that span from one side of the phospholipid bilayer to the other
• What is the function of extrinsic proteins in the cell membrane?


  They occur only on the outside surface of the lipid bilayer
• What do ion channels allow to pass through the bilayer?


  Water molecules and ions
• What are glycoproteins?


  Proteins with a polysaccharide chain extending outwards
• What role do receptors play in the cell membrane?


  They serve as binding sites for hormones
• How does cholesterol affect the cell membrane?


  It prevents loss of water and dissolved ions and regulates fluidity
• What are glycolipids?

  Carbohydrates covalently bonded to lipids
• What is the function of the glycocalyx?

  It is involved in cell-to-cell recognition
• What happens to the membrane if there is too much cholesterol?


  The membrane becomes too rigid
• What is the fluid mosaic model of the cell membrane?


  It describes the membrane as a 2D bilayer where molecules move relative to one another
• What are the two main components of phospholipids?


  A glycerol molecule and two fatty acids
• Why are phospholipids considered amphipathic molecules?


  Because they have both hydrophilic heads and hydrophobic tails
• How do proteins in the membrane contribute to its function?


  They can act as channels, receptors, or enzymes
• How do intrinsic and extrinsic proteins differ in their location within the membrane?


  Intrinsic proteins span the membrane, while extrinsic proteins are on the surface
• What is the significance of the hydrophobic layer in the cell membrane?


  It is impermeable to polar and charged molecules
• How do non-polar molecules cross the cell membrane?


  By simple diffusion through the hydrophobic layer
• What is the role of channel proteins in the cell membrane?


  They allow specific charged or polar particles to diffuse across the membrane
• What is the primary function of ATP synthase?


  It is an enzyme involved in ATP production
• What happens when a glycoprotein has a carbohydrate attached?


  It becomes involved in cell recognition
• What is the role of carbohydrates in the glycocalyx?


  They act as specific antigens
• How does the balance of cholesterol affect membrane fluidity?


  Too little cholesterol makes the membrane too fluid, while too much makes it too rigid
• What are the functions of proteins and phospholipids in the cell membrane?


  • Proteins can act as channels, receptors, or enzymes.
  • Phospholipids form a bilayer that is selectively permeable.
  • They allow non-polar molecules to cross via simple diffusion.
  • Channel proteins facilitate diffusion for specific charged/polar particles.
• What is the arrangement of phospholipids in the cell membrane?


  • Hydrophilic heads face the watery cytoplasm and extracellular space.
  • Hydrophobic tails are oriented towards the center of the bilayer.
  • This arrangement creates a barrier to polar and charged molecules.
• Endocytosis

  The active process of the cell membrane englufling material, bringing it into the cell in a vesicle
• Exocytosis


  The active process of a vesicle fusing with the cell membrane, releasing the molecules it contains.
• Phagocytosis

  The active process of the cell membrabe englufing large particles, bringing them into the cell in a vesicle
• Pinocytosis


  The active process of the cell membrane englufing droplets of fluid, brining them into the cell in a vesicle