Cell Membrane

• What is the purpose of using a cold solution in cell fractionation?

  To reduce enzyme activity and prevent degradation
• What is ultracentrifugation?

  Spinning the homogenate at high speeds
• Why is the solution used in cell fractionation isotonic?

  To prevent organelle damage from osmotic pressure
• What is the function of lysosomes?

  Contain digestive enzymes for waste breakdown
• What is the function of the cell membrane?

  Controls movement of substances in and out
• What is the common structure shared by all cell membranes?

  • Plasma membranes
  • Surround organelles and cells
• What is the specific term for the plasma membrane surrounding cells?

  Cell-surface membrane
• How do cell membranes enable different conditions inside and outside the cell?

  By regulating movement of substances
• What structure do phospholipids form in cell membranes?

  A bilayer
• What do the hydrophilic heads of phospholipids do?

  Face outward, attracted to water
• What do the hydrophobic tails of phospholipids do?

  Face inward, avoiding water
• How do lipid-soluble substances move through the membrane?

  Via phospholipids
• What are the functions of phospholipids in the cell membrane?

  • Enable entry/exit of lipid-soluble substances
  • Block water-soluble substances from passing
  • Provide flexibility and self-sealing properties
• How are phospholipids arranged in a cell membrane?

  Bilayer with heads outward and tails inward
• How do lipid-soluble substances move through the cell membrane?

  By passing through the phospholipid bilayer
• What are two functions of phospholipids in the cell membrane?

  Enable lipid-soluble entry and block water-soluble
• How are proteins embedded in the cell membrane?

  In two ways: surface and spanning
• What is the role of surface/extrinsic proteins in the cell membrane?

  Provide support or act as receptors
• How do spanning/integral proteins assist in transport?

  Form channels for water-soluble ions
• What are the functions of membrane proteins?

  • Provide structural support
  • Transport water-soluble substances
  • Facilitate active transport
  • Act as cell receptors
  • Aid cell adhesion
• What is the primary role of surface proteins in the cell membrane?

  Provide structural support or function as receptors
• How do spanning proteins assist in the transport of water-soluble ions?

  Form channels for ions to pass through
• How can spanning proteins transport molecules by changing shape?

  Act as carriers that change shape
• List three functions of membrane proteins.

  Structural support, transport, and active transport
• Where are cholesterol molecules found in the cell membrane?

  Within the cell membrane among phospholipids
• How does cholesterol affect the movement of fatty acid tails in the cell membrane?

  Pulls tails together, limiting movement
• What are two main functions of cholesterol in the cell membrane?

  • Provides strength to the membrane
  • Helps regulate membrane fluidity
• What do glycolipids consist of?

  A carbohydrate bonded to a lipid
• What is the function of the carbohydrate part of a glycolipid?

  Acts as a receptor for specific chemicals
• How does the lipid part of a glycolipid contribute to its position in the cell membrane?

  Anchors the glycolipid within the membrane
• What are two functions of glycolipids in the cell membrane?

  • Serve as recognition sites
  • Help maintain membrane stability
• What are glycoproteins composed of?

  Carbohydrate chains attached to proteins
• Where are glycoproteins located on the cell membrane?

  On the outer surface of the cell membrane
• Name two types of molecules for which glycoproteins can act as receptors.

  Hormones and neurotransmitters
• What are two functions of glycoproteins in the cell membrane?

  • Serve as recognition sites
  • Help cells attach to form tissues
• Why does the cell membrane restrict most molecules from freely diffusing?

  Lack of lipid solubility prevents passage
• How does the size of a molecule affect its ability to pass through the cell membrane?

  Large molecules cannot pass through small channels
• What happens when a molecule has a similar charge to the protein channels in the cell membrane?

  The molecule is repelled by the channels
• Why is it difficult for polar molecules to pass through the cell membrane?

  They struggle to pass through the non-polar interior
• What is the fluid-mosaic model of the cell membrane?

  • Fluid: Phospholipids can move, making it flexible
  • Mosaic: Embedded proteins vary in shape and size