B2.1 - 2.3 Bio Flashcards
What is the plasma membrane made of?
Bilayer of phospholipids and other amphipathic molecules form a continuous sheet to control the passage of substances
Phospholipid molecules
Phosphate head and two hydrocarbon tails
Are the two hydrocarbon tails hydrophobic or hydrophilic?
hydrophobic (scared of water)
Does the membrane core have low permeability or high permeability to all hydrophilic particles?
Low
low membrane permeability…
makes it possible to maintain differences in concentration (concentration gradients) across a membrane
Examples of hydrophilic particles
Ions with positive or negative charge, polar molecules, glucose
Examples of low permeability:
large molecules: proteins, starch, glycogen, cellulose
polar molecules: glucose, amino acids
ions: chloride, sodium, potassium, phosphate
Solutes near membrane…
might penetrate between the hydrophilic phosphate heads of the phospholipids
Larger the molecule…
lower the permeability
Simple Diffusion
- smaller, nonpolar (hydrophobic) molecules
- concentration gradient is high to low
- ATP is NOT required
Example of simple diffusion
if oxygen concentration inside a cell is reduced from aerobic respiration, oxygen will pass through membrane by passive (simple) diffusion
Polar molecules & simple diffusion?
Can diffuse at low rates
Two groups of membrane proteins
Integral proteins & peripheral proteins
Integral proteins
- hydrophobic on part of their surface and embedded in hydrocarbon chains in center of membrane
- may fit in both or one of phospholipid layers
- some are transmembrane proteins
Transmembrane (subset of integral) proteins
they extend across the membrane with hydrophilic parts projecting through the regions of phosphate heads on either side
Peripheral proteins
- Hydrophilic on surface, not embedded in membrane
- attached to surface of integral proteins
- some have a single hydrocarbon chain attached to them, to anchor protein to membrane surface
the more active a membrane…
the higher its protein content (ie in membranes of chloroplasts and mitochondria, active in photosynthesis and respiration
Osmosis
Due to differences in the concentration of substances dissolved in water
How do substances dissolve?
By forming intermolecular bonds with water molecules (to restrict movement of water molecules)
Higher solute concentration…
lower concentration of water molecules that are free to move
net movement of water
lower solute concentration to higher solute concentration
Aquaporins (transport protein)
Increase membrane permeability to water (ie kidney cells that reabsorb water, root hair cells that absorb water from soil)
Channel protein
Integral transmembrane protein with a pore that connects the cytoplasm to the aqueous solution outside the cell (net movement high to low)
Facilitated diffusion
one in which channel proteins are required (passive, no energy)