Biological membranes

• What surrounds all cells?

  A membrane
• What is compartmentalisation in cells?

  It is the division of cells into smaller sections using membranes
• Why is compartmentalisation important?

  It keeps different parts of the cell separate for different functions
• What is the basic structure of a phospholipid molecule?

  It consists of a fatty acid tail and a phosphate head
• How do fat-soluble and water-soluble substances pass through the membrane?

  Fat-soluble substances pass through easily, while water-soluble substances need assistance
• What model describes the structure of the plasma membrane?

  The fluid-mosaic model
• Why is the plasma membrane described as "fluid"?

  Because its components can move
• Why is the plasma membrane described as "mosaic"?

  Because it is made up of many different parts of varying sizes and shapes
• What types of proteins are found in the plasma membrane?

  Intrinsic and extrinsic proteins
• What percentage of membrane proteins are intrinsic?

  Approximately 70%
• What percentage of membrane proteins are extrinsic?

  Approximately 30%
• How do intrinsic proteins interact with the membrane?

  They go through both layers of the membrane and interact with hydrophobic fatty acids
• How do extrinsic proteins interact with the membrane?

  They only go through one layer and hold loosely to the phosphate heads
• What do channel proteins do?

  They allow specific substances to move across the membrane
• What are the functions of extrinsic proteins on the outside and inside of the membrane?

  Outside: cell signaling; Inside: associated with the cytoskeleton
• What do carrier proteins do?

  They change shape to carry substances across the membrane
• What are glycoproteins?

  Proteins with carbohydrate chains attached
• What roles do glycoproteins play?

  They can act as receptors, join cells together, or act as antigens
• Why are receptors in membranes important?

  They are vital for communication between cells
• What triggers a reaction in the cell when a chemical signal binds to a receptor?

  The binding of the signal triggers a reaction
• What are glycolipids?

  Carbohydrate chains attached directly to lipids
• What is the function of glycolipids?

  They are used as cell markers recognized by the immune system
• What is the role of cholesterol in the membrane?

  It stabilizes the membrane and maintains fluidity
• How does temperature affect the membrane's permeability?

  Higher temperatures increase permeability, while very low temperatures make it rigid
• What happens to the membrane at very low temperatures?

  The phospholipid molecules stop vibrating and become very rigid
• How does cholesterol affect membrane fluidity at high and low temperatures?

  At high temperatures, it reduces fluidity; at low temperatures, it prevents freezing
• What types of solvents disrupt the membrane?

  Solvents less polar than water or non-polar solvents
• What is the main difference between active and passive transport?

  Active transport requires energy, while passive transport does not
• What is diffusion?

  It is the movement from an area of high concentration to low concentration
• What factors increase the rate of diffusion?

  Higher temperature and steeper concentration gradients
• What is simple diffusion?

  It is the process where small, non-polar molecules pass through the membrane on their own
• What is facilitated diffusion?

  It is the process where larger or polar molecules need help from proteins to cross the membrane
• What is Fick's law related to diffusion?

  It states that the rate of diffusion is proportional to surface area and concentration difference, and inversely proportional to membrane thickness
• How does facilitated diffusion differ from simple diffusion?

  Facilitated diffusion requires proteins, while simple diffusion does not
• What is active transport?

  It moves molecules from low to high concentration and requires energy
• How does ATP function in active transport?

  ATP binds to the carrier protein, releasing energy to change its shape and move the molecule
• What is bulk transport?

  It is the movement of extremely large substances across a cell membrane
• What are the two types of bulk transport?

  Endocytosis and exocytosis
• What is exocytosis?

  It is the bulk transport of material out of the cell
• What is endocytosis?

  It is the bulk transport of material into the cell