Membranes

• What is the primary function of cell membranes?


  They act as the boundary between the cell's internal environment and the outside world.
• What are the unique properties of phospholipids that are crucial for cell membrane structure?


  Phospholipids are amphipathic, having both hydrophilic heads and hydrophobic tails.
• What are the two main components of phospholipids?


  Hydrophilic head and hydrophobic tails.
• Why are phospholipids referred to as amphipathic molecules?


  Because they have both hydrophilic and hydrophobic regions.
• What happens when phospholipids are placed in water?


  They arrange themselves into a bilayer structure with hydrophilic heads facing outwards.
• What is the arrangement of phospholipids in a bilayer?


  The hydrophilic heads face outwards and the hydrophobic tails face inwards.
• Why is the bilayer arrangement of phospholipids energetically favorable?


  It occurs spontaneously due to the hydrophobic effect.
• What makes the lipid bilayer an effective barrier?


  Its hydrophobic core and low permeability to certain substances.
• What is the composition of the hydrophobic core of the membrane?


  It is composed of fatty acid tails.
• What types of molecules have low permeability through the hydrophobic core?


  Large molecules, hydrophilic particles, ions, and polar molecules.
• What are the three reasons the membrane is an effective barrier?


  Energetic barrier, size exclusion, and charge repulsion.
• What is the energetic barrier for hydrophilic molecules trying to pass through the membrane?


  They must break hydrogen bonds with water to enter the hydrophobic core, which is energetically unfavorable.
• Why are large molecules unable to pass through the lipid bilayer?


  Because they are generally too large to fit through the tightly packed lipid bilayer.
• How does charge repulsion affect ion passage through the membrane?


  The slight negative charge of the phosphate groups can repel negatively charged ions.
• Why is selective permeability important for cells?


  It maintains cellular homeostasis and allows controlled transport of substances.
• What are the two main categories of membrane proteins?

  Integral and peripheral proteins.
• Where are integral proteins located in the membrane?


  They are embedded in one or both lipid layers of the membrane.
• What is a characteristic of integral proteins?


  They have hydrophobic regions that interact with the membrane's hydrophobic core.
• What functions can integral proteins perform?


  They may function as channels, receptors, enzymes, or cell adhesion molecules.
• Where are peripheral proteins located in the membrane?


  They are attached to one or other surface of the bilayer.
• What is a key feature of peripheral proteins?


  They do not penetrate the hydrophobic core and can be easily removed.
• What functions can peripheral proteins perform?


  They may function as enzymes, cell surface markers, cytoskeleton attachments, or regulatory proteins.
• How do membrane proteins vary in structure and function?


  They can vary in size, shape, composition, location, and function.
• What does the fluid mosaic model describe?


  It describes how proteins are distributed throughout the membrane and can move laterally.
• Who proposed the fluid mosaic model and when?


  It was proposed by Singer and Nicolson in 1972.
• What are the key components of the fluid mosaic model of membrane structure?


  • Phospholipid bilayer
  • Integral proteins
  • Peripheral proteins
  • Glycoproteins
  • Cholesterol
• What are the hydrophilic and hydrophobic regions in the membrane?


  Hydrophilic: Phospholipid heads, outer portions of integral proteins, peripheral proteins, carbohydrate chains; Hydrophobic: Phospholipid tails, inner portions of integral proteins, cholesterol.
• What are the key features of the fluid mosaic model?


  • Fluidity: Lipids and some proteins can move laterally
  • Asymmetry: Inner and outer faces of the membrane differ
  • Selective permeability: Controls what enters and exits the cell
• What is the structure of glycoproteins?


  They have a protein core with attached carbohydrate chains that are typically branched and complex.
• What is the structure of glycolipids?


  They consist of a lipid (usually sphingolipid) with an attached carbohydrate chain that is often simpler than in glycoproteins.
• Where are glycoproteins and glycolipids located in the membrane?


  They are found on the extracellular side of the membrane.
• What role do glycoproteins and glycolipids play in cell adhesion?


  They can bind to complementary molecules on other cells, important for tissue formation and maintenance.
• How do glycoproteins and glycolipids contribute to cell recognition?


  They act as "cellular ID tags," allowing cells to identify and interact with specific other cells.
• What is the significance of the specific arrangement of sugars in glycoproteins and glycolipids?


  It provides a vast array of potential "codes" for cellular recognition.