cells - transport across membranes

• What are the two main parts of a phospholipid molecule?

  A head and a tail
• What property does the head of a phospholipid have?

  The head is hydrophilic and attracts water
• What property does the tail of a phospholipid have?

  The tail is hydrophobic and repels water
• How do phospholipids arrange themselves in cell membranes?

  • They form a bilayer
  • Heads face outwards
  • Tails face inwards
  • Center of the bilayer is hydrophobic
• What is the significance of the hydrophobic center of the phospholipid bilayer?

  It prevents water-soluble substances like ions from passing through
• What are the functions of phospholipids in the membrane?

  • Allow lipid-soluble substances to enter and leave a cell
  • Prevent water-soluble substances from leaving the cell
  • Make the membrane flexible and self-sealing
• What types of proteins are found in the phospholipid membrane?

  Extrinsic and intrinsic proteins
• Where do extrinsic proteins occur in the lipid bilayer?

  On the surface of the lipid bilayer
• What is the function of intrinsic proteins?

  They span from one side of the phospholipid bilayer to the other
• What do ion channels allow to pass through the membrane?

  Water-soluble molecules/ions
• What is the role of transport proteins?

  They transport specific molecules across the membrane
• What are glycoproteins and their function?

  A protein with a polysaccharide chain involved in cell recognition
• What is the function of cholesterol in the membrane?

  It prevents loss of water and dissolved ions from the cell
• How does cholesterol affect the fatty acid tails of phospholipids?

  It pulls them together, making the membrane stronger and less fluid
• What is a glycolipid?

  A carbohydrate covalently bonded to a lipid
• What are the functions of glycolipids?

  • Act as recognition sites
  • Maintain stability of the membrane
  • Help cells attach to each other
• What are glycoproteins composed of?

  Carbohydrate chains attached to extrinsic proteins
• What are the functions of glycoproteins?

  • Act as recognition sites
  • Help cells attach to each other
  • Act as cell-surface receptors
  • Allow cells to recognize each other
• What is the fluid-mosaic model of the cell membrane?

  • Fluid: Phospholipid molecules can move relative to one another
  • Mosaic: Proteins vary in size and shape, creating a mosaic pattern
• What is diffusion?

  The passive movement of particles from higher to lower concentration
• What is a concentration gradient?

  The path from an area of higher concentration to an area of lower concentration
• What is facilitated diffusion?

  Diffusion that occurs through carrier or channel proteins
• Why do larger molecules diffuse slowly through the phospholipid bilayer?

  Because they are too big to pass easily
• How do carrier proteins facilitate diffusion?

  They change shape to release the molecule on the opposite side
• What do channel proteins do?

  They form pores for charged particles to diffuse through
• What are gated channels?

  Channels that can be opened or closed by signaling molecules
• What factors affect the rate of simple diffusion?

  • Concentration gradient: Higher gradient increases rate
  • Thickness of exchange surface: Thinner surface increases rate
  • Surface area: Larger area increases rate
• What factors affect the rate of facilitated diffusion?

  • Concentration gradient: Higher gradient increases rate
  • Number of channel or carrier proteins: More proteins increase rate
• What is active transport?

  The movement of molecules from lower to higher concentration using ATP
• What role do carrier proteins play in active transport?

  They bind to specific molecules and change shape to transport them
• When is active transport needed?

  When substances need to be moved against a concentration gradient
• What are some examples of active transport?

  • Absorption of amino acids from the gut into the blood
  • Absorption of mineral ions by the roots of a plant
• What factors affect the rate of active transport?

  • Speed of individual carrier proteins
  • Number of carrier proteins
  • Rate of respiration and availability of ATP
• How do facilitated diffusion and active transport differ?

  Facilitated diffusion does not use ATP, while active transport does
• How does glucose move from the ileum into the blood?

  Through facilitated diffusion and co-transport
• Why is active transport necessary for glucose absorption?

  To absorb all possible glucose from the ileum
• What is co-transport in relation to glucose transport?

  • A type of active transport
  • Involves the movement of glucose against its concentration gradient
• What is the role of carrier proteins in glucose transport?

  They facilitate the movement of glucose across membranes
• Who is the instructor in the video about enzyme action?

  Miss Estrich
• What are the main factors affecting enzyme action?

  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
  • Inhibitors (competitive and non-competitive)