membranes and membrane transport

Question 1

what passes the lipid membrane

Answer 1

• non-polar & lipid soluble molecules like steroids (easily)
• small uncharged molecules - oxygen, water, CO2 (readily)
  *

Question 2

what doesn’t pass the membrane

Answer 2

• mostly impermeable to uncharged polar molecules like glucose
• ions (Na+, K+, H+, Cl-, Ca2+)

Question 3

diffusion

Answer 3

spontaneous, passive movement of molecules down a concentration gradient

lipid bilayer restricts it of most molecules - only non-polars or small uncharged molecules can diffuse

Question 4

functions of membrane proteins

Answer 4

cell-cell recognition
transport of materials
receptors
enzymes
cell adhesion

Question 5

osmosis

Answer 5

the diffusion of water across a membrane to reach equilibrium with both sides
* in a hypotonic solution water moves in the cell (there is higher concentration)
- plant cell swells and undergoes turgor pressure, turgid
- animal cell may burst in lysis

• hypertonic solution water moves out of cell (higher outside)
• plant cell plasmolysis
• animal cell crenation
  = both mean shrinking
• isotonic solution there is equal movement of water in and out
• plant cell is flaccid
• animal cell is normal

Question 6

aquaporin

Answer 6

channel protein that transports water across membrane

lined with hydrophilic side chains from amino acid residues that prevent ions from passing

bidirectional

tetrameric protein composed of 4 subunits of which each have a water channel
= aquaporin has 4 water channels

Question 7

facilitated diffusion

Answer 7

assisted diffusion by transport proteins when the size/polarity of a molecule prevents passage

• channels open and close due to stimuli
• selective
• ion channels
• carrier proteins bind to the substrates and undergo a conformational change to transport to the other side
• GLUT glucose transporter (into the red blood cell)

Question 8

active transport

Answer 8

molecules need to move from low to high concentration against concentration gradient

pumps are used
requires energy, coupled w an exergonic reaction

• direct - the energy derived from ATP hydrolysis is directly used to move the molecules
• indirect - the movement of one molecule down the gradient drives the movement of the other against it

Question 9

glycolipids

Answer 9

covalently bonded carbohydrates to lipids

amphipathic, often restricted to external surface of a membrane

carbohydrate part is polar & lipid is embedded in the bilayer

contribute to membrane stability w hydrogen bonds

classified to
- glycoglycerolipids
- glycosphingolipids