topic 4 - membranes

Question 1

what are lipids

Answer 1

water insoluble (hydrophobic) molecules composed mostly of C and H atoms (hydrocarbons)

Question 2

what are biological lipids

Answer 2

triglycerides - energy storage
phospholipids and sterols - components of cell membranes

Question 3

what are fatty acids

Answer 3

building blocks of triglycerides and phospholipids

hydrocarbons with a carboxyl group at one end (C double bond to O plus OH)

Question 4

how do fatty acids vary

Answer 4

1. number of carbons in the hydrocarbon (chain length)
2. presence and number of C-C double bonds

Question 5

what is the difference between unsaturated and saturated fatty acids

Answer 5

saturated - no C-C double bonds (saturated with H)
unsaturated - has 1+ C-C double bonds

Question 6

what are triglycerides

Answer 6

energy storage molecules
3 fatty acids tails bound to a glycerol anchor
- glycerol forms an ester linkage to the fatty acid

Question 7

what are the parts of phospholipids

Answer 7

polar/hydrophilic head group
- organic molecule (any alcohol)
- phosphate
- glycerol

non polar/hydrophobic tails
- 2 fatty acid tails (one saturated and one unsaturated)

Question 8

what type of molecule is a phospholipid

Answer 8

amphipathic

Question 9

how do phospholipids form bilayers in water

Answer 9

hydrophilic heads face the water - form H bonds and electrostatic interactions with each other and H bonds with water

hydrophobic tails hide from water on the inside of membrane - interact with each other through van der waals interactions

Question 10

what is the function of biological membranes

Answer 10

compartmentalise the cell
- plasma membrane separates in from out
- internal membranes create additional cellular regions
- membranes are selectively permeable and scaffolds for communication and chemical reactions

Question 11

what is the fluid mosaic model

Answer 11

lipids and proteins coexist in the membrane
carb groups can be attached to proteins or lipids

Question 12

what is the difference between integral and peripheral proteins

Answer 12

integral = cross the bilayer (seen on both sides)
peripheral = interacting with either head groups or small part reach in

Question 13

what factors increase the fluidity of the membrane

Answer 13

• increase temp
• unsaturated fatty acids (cis double bonds) - fatty acid tails dont pack as tightly together (fewer van der waals interactions)
• shorter chain length of the fatty acid (fewer C) - there are fewer atoms available to form van der waals interactions

Question 14

what regulates membrane fluidity

Answer 14

sterols (ex: cholesterols)

Question 15

how do sterols regulate membrane fluidity from the bilayer

Answer 15

prevent excess viscosity by stopping hte phospholipids from packing too tightly together

prevent excess fluidity by filling in gaps between phospholipids

Question 16

what are sterols made of

Answer 16

amphipathic
- hydrophobic end
- fused rings (steroid nucleus) in hydrophobic hydrocarbon chain
- hydrophilic tail

Question 17

what is the order of molecules that can pass through selective permeable membrane

Answer 17

1. non polar (N2/CO2/O2) (quick diffusion, small (can slip through gaps), non polar = easy to move through hydrophobic centre)
2. small uncharged polar molecules (water, glycerol) (slow diffusion across the membrane)
3. large uncharged molecule (glucose/sucrose) (not able to diffuse - hydrophobic centre doesn’t want to let them through)
4. ions (can’t diffuse - surrounded by water wolecules which make them too big to cross)

Question 18

how does water cross membranes

Answer 18

aquaporins (water pores) - allow only water to pass through the membrane
- integral membrane protein
- hydrophilic interior (R groups) and hydrophobic exterior (interacts with the hydrocarbon chains of the phospholipids in the membrane)

Question 19

what is the relationship between concen gradient and potential energy

Answer 19

large concen gradient = high PE
equilbrium = low energy state

Question 20

what is tonicity

Answer 20

relative solute concen difference across a lipid bilayer

differences affect diffusion/osmosis across membranes

Question 21

what are the differences between hypotonic, hypertonic, isotonic

Answer 21

hypotonic (lower concen outside) - water diffuses INTO the cell (cell swells)

hypertonic (higher concen outside) - water diffuses OUT of the cell (cell shrinks)

isotonic - same concen - no net mvmt

Question 22

what are the two types of passive transport

Answer 22

simple diffusion
facilitated diffusion

Question 23

what is simple diffusion

Answer 23

small hydrophobic and small polar solutes only

direction of mvmt = with concen gradient (powered by PE)

larger concen gradient = faster diffusion

Question 24

what is facilitated diffusion

Answer 24

proteins shaped like tunnels cross the membrane and facilitate or allow the diffusion of large polar molecules or ions down/with their concen gradient

• tend to be substrate specific
• don’t require cellular energy
• rate depends on the concen gradient
• direction of the transport is reversible

Question 25

what are the types of proteins involved in facilitated transport

Answer 25

channel proteins (tunnel)
- substrate specific
- allow mvmt along concen gradient (direction can change based on concen)

carrier proteins
- carry larger molecules (glucose/sucrose)

Question 26

what is the difference between simple diffusion and facilitated diffusion relation between concen difference and rate of transport

Answer 26

simple diffusion = linear relationship
facilitated = non linear (sharp increase and plateau as it approaches max rate when all transporters are occupied)

Question 27

what is primary active transport

Answer 27

highly specific protein pumps that cross the membrane

move the solute up or against its concen gradient (from low to high)

transporter uses ATP

often used by the cell to generate chemical and electrochemical gradients

Question 28

what is secondary active transport

Answer 28

powered by energy released as a different solute moves

highly specific protein pumps that move solute up / against the concen gradient

Question 29

what is the difference between symporters and antiporters

Answer 29

symporters
- both solutes move in the same physical direction

antiporters
- solutes move in opposite physical directions