12.7 transport across membrane Flashcards
WHY IS IT FLUID
phospholipids form the bilayer which are constantly moving around one another making the membrane a fluid structure
WHY IS IT MOSAIC
the different protein molecules are unevenly distributed throughout the membrane which gives the mosaic effect
FEATURES OF FLUID MOSAIC MODEL
PHOSPHOLIPID BILAYER
CHOLSETEROL
CHANNEL PROTEINS
CARRIER PROTEINS
RECEPTOR PROTEIN
ENZYMES
GLYCOPROTEIM
AQUAPORINS
PHOSPHOLIPIDS
Hydrophilic phosphate heads and glycerol heads
Hydrophobic fatty acid tails
PHOSPHOLIPID BILAYERS allows non-polar (lipid-soluble) molecules to pass through by SIMPLE DIFFUSION but small CHARGED molecules and larger molecules are not allowed in
CHOLESTEROL
DECRESES permeability and INCREASES STABILITY of membrane
MORE CHOLESTEROL = LESS fluidity of the membrane
CARRIER PROTEINS
Transport of ions/polar molecules and large molecules e.g. glucose and amino acids by facilitated diffusion and active transport
RECEPTOR PROTEINS
Specific receptors for complementary molecules
They have specific tertiary structures. Only specific molecules can bind to specific receptor proteins
OSMOSIS
The net movement of water molecules from a high water potential to a lower water potential through a selectively permeable membrane
aquaporin
passive
water potential …
- free water molecules can move and are able to collide with the membrane exerting pressure
- presssure is known as water potential in KPa
- More free movie water molecule = more pressure = higher water potential
- pure water - every water molecule is free moving so it’s the highest water potential which is a given value of 0 kPa
- it’s a solute so it’s negative
- water is a dipole and is attracted to the charges on molecules/ions which means the number of free moving water molecules decreases
- if water is seperated by a partially/selectively permeable membrane it will diffuse down the water potential gradient where there are more free water molecules to where there a fewer free water molecules
DIFFUSION
Passive process - not requires energy (ATP)
diffusion will stop when there is equal numbers of that specific molecule
non polar through phospholipid bilayer
From higher conc to low conc
FACILITATED DIFFUSION
facilitate - help
It’s hydrophillic so it cannot pass through phospholipid layer as fatty acid tails will repel polar molecules.
channel and carrier proteins are specific shape so the only transport specific molecules that are complementary
passive
high to low concentration
FACTOR AFFECTING RATE OF DIFFUSION
TEMPERATURE - Inc kinetic energy = faster rate of diffusion of molecules
SURFACE AREA - Larger surface area for more space for molecules to pass through so faster
CONCENTRATION GRADIENT - as conc difference increases, rate of diffusion inc
DIFFUSION DISTANCE - shorter the diffusion distance (fewer membranes to cross)
Phospholipid bilayer are all the same thickness
Active transport
against concentration gradient
low-high concentration gradient
only uses carrier protein
energy supplied by ATP
requires a specifically shaped carrier protein with a complementary binding site for a complementary molecule to bind to
Active
what is the water potential of pure water?
0 kPa (nothing is dissolved in the water)
WHat are other forms of active transport?
Bulk transport - exocytosis and endocytosis (requites ATP)
Exocytosis - uses golgi vesicles to move large quantities of molecules from inside to outside the cell
Endocytosis - cell membrane is pulled inwards to create a vesicle.
