Lecture 3 - Intro. to Membranes

Question 1

What is the membrane composed of?

Answer 1

phospholipid bilayer

Question 2

How do double-tailed phospholipids form?

Answer 2

• form a bilayer because they are cylindrical

- spontaneously form

Question 3

What shape do single-tailed phospholipids form?

Answer 3

• micelle forms because they are conical

Question 4

How often does lateral movement and flip flop activity occur as phospholipids move within the bilayer?

Answer 4

• lateral movement occurs rapidly

- flip flop is very rare because the polar head is not stable in the hydrophobic core

Question 5

What happens when a membrane is exposed to high temperatures? List adaptions to fix this.

Answer 5

• the gap increases = increased permeability
• have more kinetic energy = move faster
• adaptions:
  1) increase hydrocarbon tail length
  2) decrease C=C
  3) increase cholesterol content

Question 6

What happens when a membrane is exposed to low temperatures? List adaptations to fix this.

Answer 6

• the gap decrease = the permeability and flexibility of the membrane reduces
• adaptions:
  1) increase C=C
  2) decrease the tail length
  3) increase cholesterol

Question 7

What is The Fluid Mosiac Model?

Answer 7

• states that the membrane is a fluid-structure (phospholipids) with a mosaic of different proteins embedded in or attached to a double bilayer of phospholipids

Question 8

What does permeable mean?

Answer 8

a substance that can freely diffuse across the phospholipid bilayer (small and uncharged)

Question 9

What does impermeable mean?

Answer 9

a substance that cannot cross the hydrophobic core because they are either: too big or too polar
- ions are the least permeable

Question 10

What is one exception when it comes to substances crossing the phospholipid bilayer?

Answer 10

water!! it is polar but diffuses by osmosis

• it undergoes a dipole movement where the unequal charge distribution disappears long enough to cross the membrane
• it diffuses SLOWLY

Question 11

What is passive transport?

define diffusion and osmosis

Answer 11

• for permeable substances
• molecules have a thermal motion that can diffuse
• diffusion = movement of molecules from an area of high concentration to an area of low concentration
• osmosis = passive diffusion of water
• water follows solute

Question 12

What is a hypotonic environment?

Answer 12

• water rushes in

- animal cells can burst (osmotic lysis), plant cells have a cell wall that prevents bursting

Question 13

What is a hypertonic environment?

Answer 13

• water rushes out

- the cells may shrink, in plant cells plasmolysis (pulling away from membrane from cell wall) can occur

Question 14

What is an isotonic environment?

Answer 14

• no movement of water

- solute inside = solute outside

Question 15

What are aquaporins?

Answer 15

a type of transmembrane channel that facilitates osmosis because the movement of water across a membrane isn’t as fast as through a channel

Question 16

What is facilitated diffusion?

Answer 16

• molecules move DOWN their concentration gradient using a channel protein (transmembrane protein)

Question 17

What are the two different types of proteins in facilitated diffusion?

Answer 17

• channel protein (“funnel”) = integral membrane protein, allows transport of a specific solute without changing shape
• carrier protein (“revolving door”) - span bilayer, allows transport of a specific solute by changing its shape

Question 18

What is active transport?

Answer 18

• transport molecules UP the concentration gradient

- requires energy = ATP, redox rxns, light

Question 19

What is an example of active transport?

Answer 19

• sodium/potassium pump
• active in all cells all the time, except red blood cells
• cotransport
• electrogenic

Question 20

What is the electrochemical gradient?

Answer 20

• when there is a charge difference and a concentration difference due to transport of a charged molecule

Question 21

What is cotransport?

Answer 21

• transport of two molecules simultaneously

- chemical gradient or electrical gradient (or both) are a source of potential energy

Question 22

What is coupled transport?

Answer 22

• the use of energy released by one gradient to establish another gradient

Question 23

What is bulk transport?

Answer 23

• molecules that must enter or exit the cells but are too big to pass through a transport protein must be transported using a bulk transport method
• involves the formation of vesicles
• membrane is flexible, bend into different shapes
• can either undergo: exocytosis or endocytosis

Question 24

What is exocytosis?

Answer 24

• secretion
• bulk transport out of the cell
• refer to notes for diagram

Question 25

What is endocytosis?

Answer 25

• bulk transport into the cell
• generalized phagocytosis
• non-specific (anything in the extracellular fluid is brought into the cell)
• refer to notes for diagram

Question 26

What is receptor-mediated endocytosis?

Answer 26

• the endocytosis of a specific ligand
• ligand = anything that binds a receptor
• receptor = integral membrane protein that recognizes and binds a specific ligand
• receptors congregate at clathrin-coated pits