biological membranes

• What type of structures are membranes considered to be in all cells?

  Vital
• What does the cell surface membrane do?

  Separates internal and external cell environments
• What are intracellular membranes also known as?

  Internal membranes
• What do intracellular membranes form within the cell?

  Compartments
• What is another structure formed by intracellular membranes?

  Vacuoles
• Besides separating areas, what do membranes control?

  The exchange of materials
• What is a key characteristic of membranes regarding permeability?

  Partially permeable
• What kind of barriers do membranes form?

  Partially permeable barriers
• Between what locations do membranes form barriers?

  Cell and environment, cytoplasm and organelles
• What are the four processes by which substances cross membranes?

  Diffusion, facilitated diffusion, osmosis, active transport
• What role do membranes play in cell signaling?

  Acting as an interface for communication
• How do membranes compartmentalize different regions within the cell?

  Formed from phospholipid bilayers
• What do lysosomes contain?

  Hydrolytic enzymes
• What would happen if the hydrolytic enzymes in lysosomes were not compartmentalized?

  Breakdown of cellular components
• When was the fluid mosaic model of membranes first outlined?

  1972
• What processes does the fluid mosaic model help to explain?

  Passive and active movement
• What else does the fluid mosaic model help to explain?

  Cell-to-cell interactions
• What is another process that the fluid mosaic model helps to explain?

  Cell signalling
• Why does the fluid mosaic model describe cell membranes as 'fluid'?

  Phospholipids and proteins can move
• How do phospholipids mainly move within the membrane?

  Sideways, within their own layers
• How do the proteins move within the phospholipid bilayer?

  Move about within it
• Why are cell membranes described as 'mosaics' in the fluid mosaic model?

  Scattered protein pattern resembles a mosaic
• What are the four main components of the fluid mosaic model of membranes?

  Phospholipids, cholesterol, glycoproteins and glycolipids, transport proteins
• What basic structure do phospholipids form in the membrane?

  The phospholipid bilayer
• What part of the phospholipid forms a hydrophobic core?

  The tails
• What kind of barrier do phospholipid bilayers act as?

  Barrier to most water-soluble substances
• Why do phospholipid bilayers act as a barrier to most water-soluble substances?

  Non-polar fatty acid tails prevent passage
• What does the phospholipid barrier ensure regarding water-soluble molecules?

  Sugars, amino acids, and proteins cannot leak
• What is the other thing that the phospholipid barrier ensures regarding unwanted water-soluble molecules?

  Unwanted molecules cannot get in
• How can phospholipids be chemically modified to act as signalling molecules?

  Moving within the bilayer
• What is another method for phospholipids to be chemically modified to act as signalling molecules?

  Being hydrolysed
• What happens when phospholipids are hydrolysed?

  Releases smaller water-soluble molecules
• What is the orientation of phospholipids in a bilayer?

  Hydrophobic tails inwards, hydrophilic heads outwards
• What effect does cholesterol have on membrane fluidity at low temperatures?

  Increases fluidity
• How does cholesterol increase membrane fluidity at low temperatures?

  Stops phospholipid tails packing closely
• What effect does cholesterol have on membrane stability at higher temperatures?

  Stabilizes the cell membrane
• How does cholesterol stabilize the cell membrane at higher temperatures?

  Stops membrane becoming too fluid
• How does cholesterol molecules interact with phospholipids in the membrane?

  Bind to the hydrophobic tails
• What does cholesterol do to the packing of phospholipids?

  Causes phospholipids to pack more closely
• What effect does cholesterol have on the impermeability of the membrane to ions?

  Also affected by cholesterol