Chapter 6 - Energy, Enzymes, and Metabolism

• What is the main structure of biological membranes according to the fluid mosaic model?

  A lipid-protein bilayer
• What do phospholipids consist of in the cell membrane?

  They have polar hydrophilic heads and hydrophobic fatty acid tails.
• How does cholesterol affect the cell membrane?

  It modulates fluidity and maintains membrane integrity.
• What factors influence the fluidity of membranes?

  Lipid composition and temperature.
• What are the three types of membrane proteins?

  Integral, peripheral, and anchored proteins.
• What distinguishes integral membrane proteins from peripheral membrane proteins?

  Integral proteins are embedded in the bilayer, while peripheral proteins do not penetrate it.
• What role do carbohydrates play on the outer surface of membranes?

  They serve as recognition sites for other cells and molecules.
• What is the function of cell adhesion and recognition in tissues?

  • Cells arrange themselves in tissues through cell recognition and adhesion.
  • These processes depend on surface proteins and carbohydrates.
  • Adhesion can result from interactions between carbohydrates and proteins.
• What are cell junctions and their types?


  Specialized structures that hold cells together, including tight junctions, desmosomes, and gap junctions.
• What is the function of integrin in cell adhesion?

  Integrin binds to the extracellular matrix outside epithelial cells and to actin filaments inside the cells.
• What is selective permeability in membranes?


  It means that some substances can pass through the membrane while others cannot.
• What is the difference between passive transport and active transport?

  Passive transport requires no energy, while active transport requires energy input.
• What is diffusion?


  The process of random movement toward equilibrium, moving from areas of higher concentration to lower concentration.
• What factors affect the rate of diffusion?

  Size and mass of molecules, temperature, density of the solution, concentration gradient, area, and distance.
• What is osmosis?


  The diffusion of water across a selectively permeable membrane.
• What are isotonic, hypertonic, and hypotonic solutions?

  Isotonic: equal solute concentrations; hypertonic: higher solute concentration; hypotonic: lower solute concentration.
• What happens to animal cells in hypotonic and hypertonic solutions?

  They may burst in hypotonic solutions or shrink in hypertonic solutions.
• What is turgor pressure in plant cells?

  It is the internal pressure that prevents excessive water from entering the cell.
• What is facilitated diffusion?


  It is the process where polar and charged molecules diffuse with the help of protein channels or carriers.
• What are channel proteins?


  Integral membrane proteins that form a tunnel for molecules to pass through.
• What are ion channels?

  Channel proteins with hydrophilic pores that can be gated to control ion passage.
• What are aquaporins?


  Special channels that allow water to cross membranes.
• How do carrier proteins function?

  They transport polar molecules, such as glucose, across membranes by changing shape.
• What is active transport?

  It moves substances against a concentration and/or electrical gradient and requires energy.
• What is the energy source for active transport?

  Adenosine triphosphate (ATP).
• What are the three types of proteins involved in active transport?

  Uniporter, symporter, and antiporter.
• What is primary active transport?

  It requires direct hydrolysis of ATP.
• What is the sodium-potassium pump?


  An integral membrane glycoprotein that exports three Na⁺ ions and imports two K⁺ ions.
• How does secondary active transport work?

  It uses the concentration gradient established by primary active transport to move other substances against their gradient.
• How do large molecules enter and leave a cell?

  • Large molecules like proteins and polysaccharides cannot cross the membrane directly.
  • They enter or leave the cell via membrane vesicles.
  • Processes include endocytosis and exocytosis.
• What is endocytosis?


  A process that brings molecules and cells into a eukaryotic cell by folding the membrane inward to form a vesicle.
• What is phagocytosis?


  A type of endocytosis where molecules or entire cells are engulfed.
• What is pinocytosis?


  A type of endocytosis that brings small dissolved substances or fluids into a cell.
• What is receptor-mediated endocytosis?


  A highly specific process where macromolecules bind to receptor proteins on the cell membrane.
• How do mammalian cells take in cholesterol?

  Through receptor-mediated endocytosis involving low-density lipoprotein (LDL).
• What is exocytosis?


  A process where materials packaged in vesicles are secreted from a cell when the vesicle membrane fuses with the cell membrane.
• What is the importance of aquaporin membrane channels?

  A lack of aquaporins in the kidneys can cause more water in the urine and frequent urination.
• How do aquaporins function in plants?

  They are important in root cells for water uptake and in vacuole membranes.
• What is the potential application of aquaporins in synthetic membranes?


  They might be used to purify or desalinate water.