Biological Membranes

• What does the fluid-mosaic model consist of?

  The phospholipid bilayer, proteins, glycoproteins, glycolipids and cholesterol

  
• Phospholipids have...?


  Hydrophilic phosphate heads that interacts with the aqueous environments and hydrophobic fatty acid tails which cluster together, repelling the water

  
• Roles of the cell surface/plasma membrane

  (1) Compartmentalisation --> Provides specific conditions for reactions to occur in

  (2) Site of chemical reactions --> Contains proteins/enzymes involved in chemical reactions

  (3) Plays a role in communication and has receptors (where drugs and hormones can bind)
• What are intrinsic proteins and give examples

  Intrinsic proteins are embedded in the plasma membrane

  Protein carriers

  Channel Proteins

  
• What are extrinsic proteins and give examples

  Extrinsic proteins are on the surface of the plasma membrane

  Glycoproteins

  Glycolipids

  
• Carrier Proteins

  Transports and bind with ions and larger molecules (e.g. glucose and amino acids) and uses energy to transport these molecules. It changes shape to transport them from one side of the membrane to the other

  
• Channel Proteins

  Tubes that fill up with water to enable water-soluble molecules and ions to diffuse

  
• Glycoproteins (carbohydrate + phospholipid)

  Provides mechanical support

  Act as receptors for cell recognition
• Glycoprotein (carbohydrate + protein)

  Provides mechanical support

  Act as receptors for cell recognition
• Cholesterol

  Adds stability and regulates fluidity

  Restricts lateral movement of other molecules in the membrane

  Makes membranes less fluid at higher temperatures
• What are the factors affecting membrane structure and permeability?

  Temperature

  Solvents
• High temperatures

  High temperatures increase kinetic energy of the phospholipids and breaks the intermolecular forces between them. This increases fluidity of the membrane, increasing permeability. This makes it easier for particles to cross the membrane.

  High temperatures denature carrier and channel proteins
• Solvents

  Organic solvents (such as alcohol) dissolve the phospholipid bilayer. This damages the bilayer increasing fluidity and permeability of the membrane
• What are the 6 modes of transport?

  Simple Diffusion

  Facilitated Diffusion

  Osmosis

  Active Transport

  Exocytosis

  Endocytosis
• What are the passive modes of transport

  Simple Diffusion

  Facilitated Diffusion
• What are the active modes of transport? (requires ATP)

  Osmosis

  Active Transport

  Endocytosis

  Exocytosis
• Simple Diffusion

  The net movement of molecules from an area of high concentration to a low concentration.

  Does not require ATP

  Molecules have to be lipid-soluble and small

  
• Facilitated Diffusion

  The movement of ions and polar molecules (using carrier and channel proteins).

  It is a passive process down the concentration gradient

  
• Osmosis

  The movement of water from an area of a higher water potential to an area of a lower water potential (more negative) across a partially permeable membrane

  
• What are the types of solutions?

  Isotonic

  Hypotonic

  Hypertonic

  
• Isotonic Solution

  The water potential of the solution is the same as the cell

  
• Hypotonic Solution

  The water potential of the solution is more positive (closer to 0) than the cell. More water compared to solute

  This means that water moves from the solution into the cell, causing it to swell (turgid in plants)

  It could eventually burst

  
• Hypertonic Solution

  The water potential of the solution is more negative than the cell. More solute compared to water.

  This means that water will move out from the cell by osmosis into the solution (crenation in animals and plasmolysis in plants)

  
• Active Transport

  The movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins

  It is selective (only certain molecules can bind to the receptor sites).

  ATP is hydrolysed to ADP + Pi.

  Causes protein to change shape and open towards the inside of the membrane and the molecule is released to the other side of the membrane

  Pi is also released which reverts the protein back to its original shape

  
• What are the 2 types of active transport?

  Endocytosis

  Exocytosis
• Endocytosis


  The bulk transport of molecules into the cell

  The cell surface membrane bends inwards and surrounds the molecule to form a vesicle. The vesicle pinches off and moves within the cytoplasm

  Requires ATP for the cell surface membrane to change shape and engulf the material

  
• Exocytosis

  The bulk transport of molecules out of the membrane.

  Vesicles move towards the cell surface membrane, fuse with it and the contents of the vesicle is released outside of the cell

  Requires ATP to move the vesicle across the cytoskeleton