Chapter 5- plasma membranes

• State three roles of the plasma membrane

  • Acts as a barrier between areas
  • Site of chemical reactions
  • Cell signalling
• What do cell membranes not do?

  • Provide support for the cell
• One difference between the intracellular and extracellular membrane?

  Extracellular membrane partakes in cell to cell signalling, intracellular membrane doesn’t
• What is the role of cholesterol in the cell membrane?

  Binds to fatty acid tails, reducing or increasing the packing of the membrane, reducing or increasing membrane fluidity (maintaining or regulating membrane fluidity)
• Why must glucose travel through the phospholipid bilayer through facilitated diffusion?

  • The bilayer acts as a barrier
  • Glucose isn’t soluble in phospholipid bilayer because of polar -OH groups (fatty acid tails are hydrophobic)
• State how the plasma membrane remains stable

  • Cholesterol- binds to fatty acid tails and regulates fluidity
  • Hydrophobic region- helps form bilayer and separate two aqueous regions
• State the role of membranes WITHIN the cell

  • Compartmentalisation- surround (named) organelles
  • As organelles need to be separated from cytoplasm
  • Sites of chemical reactions
  • Electron carriers/photophosphorylation
  • Attachment sites for enzymes or pigments
  • Allow formation of concentration gradients
• What are the two types of proteins in the cell membrane?

  Intrinsic and extrinsic proteins
• What are intrinsic proteins?

  • Transmembrane proteins embedded through both layers of a membrane
  • AAs with hydrophobic R groups on their external surfaces
  • These R groups interact with hydrophobic core of membrane, keeping it in place
• Are channel and carrier proteins intrinsic or extrinsic proteins?

  intrinsic
• Name 3 intrinsic proteins

  • Na/K pump
  • Channel proteins
  • Carrier proteins
• Describe structure and function of channel proteins (2 bullets)

  • Provide hydrophillic channel allowing passive movement of polar molecules and ions down their concentration gradient through membranes
  • Held in position by interactions between hydrophobic core of membrane and hydrophobic R groups on the outside of the proteins
• describe the structure and funtion of glycoproteins

  • Intrinsic
  • Attached carbohydrate chains of varying lengths
  • Play a role in cell adhesion
  • Receptors for chemical signals
  • involved in cell signalling
  • Receptors for neurotransmitters and hormones
• Describe the structure and function of glycolipids

  • Lipids with attached carbohydrate chains
  • Cell markers/antigens
  • Recognised as foreign or non foreign
• Describe the structure and function of carrier proteins

  • involved in both passive and active transport in cells
  • Often involves the shape of the protein changing
• Describe the role of extrinsic proteins

  • Present in one side of the bilayer
  • Hydrophilic R groups on outer surface
  • Interact with polar phospholipid heads or intrinsic proteins
  • Can be preset within either layer and some move in between layers
• Differences between extrinsic and intrinsic proteins?

  • Extrinsic- present on one side of the bilayer, Intrinsic- Present throughout the bilayer
  • Extrinsic have hydrophilic R groups on outer surface, intrinsic have hydrophobic R groups on outer surface
• Describe how plasma membranes have a role in cell signalling (PPQ)

  • Release of signal molecule by exocytosis
  • Glycoproteins/lipids have receptors
  • Receptor/signal is specific
  • shape of receptor and signal are complementary
  • attachment of signal molecule causes change of cell surface
  • cell surface allows entry of some signal molecules
• Describe the role of cholesterol in the plasma membrane

  • Lipid with hydrophobic and hydrophilic end
  • Regulates membrane fluidity
  • Positioned between phospholipids, hydrophilic end interacting with the heads and hydrophobic end interacting with the tails, adding stability and stopping membranes from becoming too rigid
  • Stop phospholipid molecules from crystallising
• How do solvents disrupt the cell membrane?

  • dissolve membranes, disrupting cells
  • Membrane becomes more fluid and permeable
  • as gaps form in membrane
• Outline the role of membranes within cells (PPQ)

  • Compartmentalisation- separation of two different environments
  • Maintain correct conditions for sites of chemical reactions
  • Allows formation of concentration gradients
  • Provides surface for attachments for enzymes