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Senanu's Bio class

Chapter 6 – Lipids & membranes

Lipids

OBJECTIVE: Describe the structure and function of different types of lipids (fats, phospholipids, & sterols).

  1. Fats, also called _______________________________________ , are formed when three ______________________________ are each joined to a _________________________________ via ____________________________________reactions.
  2. How many water molecules are “lost” during the formation of a fat?
  3. Describe (or show with a diagram) the difference in structure between saturated and unsaturated fats.
  4. Explain why unsaturated fats are more likely to be liquid (oils) at room temperature, and saturated fats are likely to be solid.

  5. Draw a glycerol molecule. Attach 2 saturated and 1 unsaturated fatty acids to it using the appropriate linkage.

    OBJECTIVE: Describe the structure and role of phospholipids in membranes.

  6. Use a cartoon to show the difference between a triglyceride and the phospholipid you drew above.
  7. Draw a diagram of a phospholipid bilayer.
  8. Explain how the hydrophobic and hydrophilic structures in phospholipid molecules are important in the formation of phospholipid bilayer membranes.
  9. How do you think a water molecule would interact with the inside of a phospholipid bilayer?
  10. What is characteristic of all steroids?
  11. What differs between steroids?

Membranes

OBJECTIVE: Describe the structure and function of membrane molecules, including phospholipids and proteins.

  1. What does the term amphipathic mean?
  2. Draw a cartoon of a phospholipid and label the two regions that make it amphipathic.
  3. Describe the fluid mosaic model of membranes.

  4. Assess how each of the following factors affects membrane fluidity

    Feature Effects on fluidity Reasons for the effect
    Phospholipids have saturated tails
    Phospholipids have unsaturated tails
    Temperature
    Cholesterol at moderate to high temperatures
    Cholesterol at low temperatures
  5. Look at Figure 6.17. What can you conclude about α-helices’ affinity for water?

  6. What is the difference between peripheral and integral proteins?

    OBJECTIVE: Describe how substances move across lipid bilayers passively: Diffusion & Osmosis

  7. Give a definition of diffusion.
  8. In which direction (relative to concentration gradients) will solutes diffuse?
  9. What is the meant by the term ‘passive transport’? What makes it ‘passive’?
  10. What is osmosis? What is the relationship between osmosis and diffusion?
  11. Is it possible for large, or hydrophilic molecules to passs through the membrane? What classes of molecules allow this?
  12. Draw a picture of a liquid-filled bag made of semipermeable membrane in a beaker of water. The bag has a high concentration of salt within it. The water of the beaker is pure water.
    • label which solution (inside the bag or the contents of the beaker) is hypertonic
    • label which solution is hypotonic
    • indicate on your picture which direction water will move through the membrane
    • what will happen to the size of the bag after a period of time?
    Feature Effects on permeability Reasons for this effect
    Size of solute Small molecules pass through membrane
    more easily than large molecules    		 Small molecules are able to fit through
    the tight spaces between the phospholipids
    Charge or polarity of solute
    Saturation of fatty acids in phospholipids
    Length of fatty acid tails in phospholipids
    Presense of cholesterol
    Temperature
  13. (review) Draw the structure of an amino acid in its ionized form (as it exists in the cell).

  14. Do you think a lipid bilayer is permeable to amino acids? Why or Why not?

    OBJECTIVE: Describe how substances move across lipid bilayers via active transport

  15. What is meant by ‘active’ transport? How is it different from ‘passive’ transport?
  16. Why doesn’t it make sense for cells to actively transport (pump) uncharged non-polar molecules across their membrane?
  17. Look at figure 6.25. In this figure, sucrose is moving down its concentration gradient by diffusion, but it can also move UP its concentration gradient by via secondary active transport (cotransport). Explain how this works and how it is different from simple active transport.

  18. What is meant by an ‘electrochemical gradient’. How is this different from a ‘concentration gradient’?

    OBJECTIVE: Describe how cells move large quantities or large materials into their interior without requiring those substanes to pass through a membrane.

  19. In general, describe how cells transport materials into the cell without passing them through a membrane.

Do the following in or after class…

  1. Draw a cartoon of a single phospholipid molecule. Indicate which parts of the molecule have full or partial charges, and what those charges are (+ or -). Draw water molecules interacting with these charged regions, and show how water molecules don’t interact with other regions.
  2. Why are diffusion and osmosis both considered to be ‘passive’?
  3. Nerve cells (neurons) spend a lot of energy pumping Na+ and K+ ions. Under normal conditions, where is there a net positive and where is there a net negative charge (inside or outside the cell)? Describe what would happen to brain function if energy stores in those cells ran critically low?
  4. How is secondary active transport (cotransport) different from active transport?