Lecture #3- Introduction to Membranes

Question 1

what is the phospholipid bilayer? draw the micelle and bilayer

Answer 1

• amphipathic nature allows phospholipids to spontaneously form membranes
• bilayer: is cylindrical with 2 fatty acid tails
• micelle: conical, have single tails and they from in a circular fashion
• they are mobile within the bilayer, moving freely laterally because they are only associated based on hydrophobicity and no covalent bonds which is rapid and frequent
• the inside is called the hydrophobic core, where water is excluded
• flip/flop movement can happen but it’s rare, facilitated b enzymes called flipases

Question 2

effect of temp on membrane fluidity: high temp

Answer 2

high temp = phospholipids have more kinetic energy
- it increased fluidity and decreased integrity(disrupts semi-permeable nature)
adaptations:
1. increase HC tail length ( increase in hydrophobicity)
2. decrease C=C
3. increase cholesterol content: increases hydrophobicity and acts as a speed bump

Question 3

effect of temp on membrane fluidity: low temp

Answer 3

• have less kinetic energy
• decrease in fluidity, flexibility, and integrity (disrupts semi-permeability)
  adaptations:
  1. decrease HC tail length, more unlikely to unstick
  2. increase C=C, creates more kinks and therefore more space
  3. increase cholesterol - acts as a spacer, wedged in b/w

Question 4

draw the bilayer with the two membranes

Answer 4

pg 4 of notes
1. integral membrane protein interacts with the hydrophobic core of membrane
2. peripheral membrane protein - associate with cytoplasmic face of membrane via integral membrane proteins
protein-protein interactiosn often involve hyrdoph… association

Question 5

draw the fluid model of the phospholipid bilayer: label the extracellular, cytoplasm, fibronectin, cholesterol, actin filaments, integral and peripheral membrane protein, glycolipids, glycoproteins, collagen

Answer 5

pg 4 of notes

Question 6

transport within the bilayer: define permeable and impermeable and the exception

Answer 6

• permeable = a substance that can freely diffuse across the bilayer
• impermeable = a substance that cannot cross the hydrophobic core either because its too big or too polar, ions are least permeable
• water is polar but diffuses redily by osmosis, undergoes dipole moment where the unequal charge distribution disappears long enough to cross the membrane

Question 7

what is passive transport? and the 3 different types of environment

Answer 7

• permeable substances move down [ ] gradient across bilayer
• hypotonic enviro: water rushes in and can cause animal cells to burst and cell walls prevent osmoticlysis
• isotonic: no net movement of water
• hypertonic: water rushed out, animal cells shrink and plant cells undergo plasmolysis

Question 8

facilitated diffusion: channel and carrier and draw them out to help explanation !

Answer 8

• transport down the [ ] gradient that uses a protein transporter
  1. channel - integral membrane protein with a specific pore to allow transport of a specific solute
  2. carrier - integral membrane protein that transports a specific solute using a conformational change